JP2959681B2 - Photoelectric conversion device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device, and more particularly to a photoelectric conversion device utilizing an avalanche effect for amplifying photogenerated carriers by impact ionization.

The present invention also relates to a low-noise photoelectric conversion device which is suitably used especially for a photometric sensor of a camera, an image sensor for an image reading device such as a facsimile, a copying machine, or a light receiving sensor of an optical communication device. It concerns the device.

[0003]

2. Description of the Related Art In information transmission technologies using light as a medium for information signals, for example, in video information systems, optical communications, other industries, and consumer fields, semiconductor light receiving elements for converting optical signals into electric signals are the most important. It is one of the basic components, and many are already in practical use. Generally, a semiconductor light receiving element is required to have a high signal-to-noise ratio for its photoelectric conversion characteristics. Among these, an avalanche photodiode (hereinafter, referred to as an APD) utilizing the avalanche effect is a promising candidate for a semiconductor light receiving element that satisfies such requirements because it has a high gain and a fast response speed.

At present, many APDs have already been put into practical use, particularly as a semiconductor light receiving element in an optical communication system, using a compound semiconductor such as InGaAs as a material. Development of improvement in basic performance is being promoted, and application to other fields, for example, visible light receiving elements and the like is also desired.

FIG. 41 is a longitudinal sectional view showing the structure of a conventional APD for optical communication. In the figure, 101 is an n ⁺ type I
nP layer, 102 is n-type InGaAs layer, 103 is n-type InP
Layer 104 is a p ⁺ -type InP layer. Here, n-type InGa
As layer 102, n-type InP layer 103, p ⁺ -type InP layer 10
The layer 4 is formed in a mesa shape. p ⁺ type InP layer 10
A p-electrode 106 is formed on the upper surface of the substrate 4, leaving a window 105, and an n-electrode 107 is formed on the back surface of the n ⁺ -type InP layer 101. 108 is a passivation film. Where p
When the electrode 106 and the n-electrode 107 are biased in the reverse direction and light is irradiated from the window 105, light is emitted from the n-type InGaAs layer 10
2 (which becomes a light absorbing layer), and light-electric conversion is performed. That is, the electron-hole pairs formed in the n-type InGaAs layer 102 travel toward the n-electrode 107 and the p-electrode 106, respectively. Since the n-type InP layer 103 (which becomes a multiplication layer) has a strong electric field, a Nadare phenomenon occurs in which a large number of electron-hole pairs are formed during a hole traveling process, and a plurality of n-type InP layers 103 A multiplication action of forming individual electron-hole pairs occurs.
As a result, signals can be detected even with weak incident light. But,
In the conventional structure, the practical multiplication is as small as about 2, and the fluctuation inherent in the multiplication process causes excessive multiplication noise to lower the signal-to-noise ratio (S / N ratio). Had two drawbacks.

The noise generated in the avalanche multiplication process is, for example, an IEEE Transactionson Electron Devices
According to RJ McIntyre's paper in the 13th edition (January 1966), pages 164 to 168, it strongly depends on the ratio k = β / α between the ionization rate α of electrons and the ionization rate β of holes. It is known to

[0007] Here, the ionization rate of electrons is the rate at which electron-hole pairs are generated by impact ionization when electrons are accelerated by an electric field. The hole ionization rate is the ratio of impact ionization due to holes. Furthermore, according to this paper,
It has been clarified that, in order to obtain a low-noise APD, k should be small when performing electron multiplication and large when performing hole multiplication. That is, it is important to obtain a high signal-to-noise ratio in an APD by avalanche multiplying only a carrier having a higher ionization rate in a material having a significantly different ionization rate of carriers (electrons or holes). According to this paper, the excess noise figure F is 2 as the limit of noise reduction achieved when avalanche multiplication of only one carrier is performed.
It is stated that In an ideal case where no noise is generated, F should be 1, and the limit of F = 2 implies that some mechanism for generating noise still exists. The mechanism of this mechanism is that when performing avalanche multiplication, the places where ionization (inverse Auger generation), which is the elementary process of avalanche multiplication, fluctuates individually, and the sum is added to cause fluctuation of the multiplication factor as a whole. Conceivable.

In consideration of the above, in order to perform avalanche multiplication without generating noise, a place where ionization, which is an elementary process, is specified in the element, and ionization at the place where the ionization occurs is performed. It is necessary to specify the probability of Furthermore, in order to perform avalanche multiplication with high gain, it is important to make the probability of ionization as close to 1 as possible.

In view of the two drawbacks of the above-described small degree of multiplication and a decrease in the signal-to-noise ratio (S / N ratio), as an APD for optical communication, for example, F. Capasso et al.
-157179 and IEEE Electron Device Letters
EDL3 edition (1982), pp. 71-73, low-noise APD usable for optical communication systems mainly made of compound semiconductors belonging to group III-V by molecular beam epitaxy (MBE) Has been proposed.

The element is formed by changing the composition ratio of the constituent materials (for example, if the compound semiconductor belonging to the group III-V is the constituent material, the composition ratio of the group III semiconductor to the group V semiconductor). Numerous semiconductor layers whose band gap is continuously changed from a narrow side to a wide side are stacked, and ionization is promoted by utilizing a step-like transition portion (hereinafter abbreviated as a step-back structure) of an energy band formed at that time. It features a multi-layer heterojunction structure. The schematic structure of the proposed device will be described with reference to FIGS.

FIG. 42 is a longitudinal sectional view of this device, and shows a step-back structure layer 20 composed of five layers serving as multiplication layers.
1, 203, 205, 207, and 209 are sandwiched between a p-type semiconductor layer 211 and an n-type semiconductor layer 215 serving as light absorption layers.
14 are in ohmic contact with the n-type semiconductor layer 215, respectively.

FIG. 43 is a structural diagram of the energy band of the band gap gradient layer when the device is not biased, and shows three band gap gradient layers. Each layer has a composition that changes the band gap linearly from a narrow band gap Eg2 to a wide band gap Eg3.

The magnitudes of the conduction band and the valence band step back are represented by ΔEc and ΔEv, respectively. As described later, ΔEc is set to be larger than ΔEv mainly in order to easily ionize electrons.

FIG. 44 is a structural diagram of an energy band when a reverse bias voltage is applied to this element. The reverse bias voltage does not need to be a strong electric field as compared with the APD shown in FIG.

Here, when light enters from the p-type semiconductor layer 211, the light absorbed by the p-type semiconductor layer and each step-back structure layer undergoes photoelectric conversion in the same manner as in the above-described APD.
The formed electron-hole pairs correspond to the respective n-type semiconductor layers 21.
5, while traveling toward the p-type semiconductor layer 211, the difference from the APD shown in FIG. 41 is that the energy step ΔEc of each step-back structure (for electrons, ΔEv for holes) is the ionization energy. When it gets bigger,
The electrons are ionized, generating electron-hole pairs, producing a multiplication effect. Of course, the multiplication occurs 2 ^{n with} respect to the number n of the layers because each of the step-back structure layers performs the same operation. For example, ideally, by setting ΔEcＥΔEv ≒ 0, the ionization rate of holes can be extremely reduced as compared with the ionization rate of electrons, so that noise is lower than that of the above-described APD.

That is, the bias voltage is controlled by the step-back structure layers (band-gap gradient layers) 201, 203, and 205.
And 209 are applied so that at least depletion occurs and an electric field (drift electric field) is generated to such an extent that carrier drift occurs in the band gap gradient layer but ionization does not occur. The light hν is applied to the depletion region next to the p-type semiconductor layer 211, that is, the bandgap gradient layer 201.
To generate electrons in the conduction band and holes in the valence band. The generated electrons drift in the layer 201 toward the step back of the first conduction band. There is already an energy step ΔEc at the step back,
Since the electrons can supplement the energy required for ionization by this energy step ΔEc, the probability of the electrons ionizing immediately after the stepback is increased. Here, when the energy step ΔEc is equal to or larger than the ionization energy of the electron, and when the energy shortage can be supplied from the drift electric field even if the energy step ΔEc is smaller than the ionization energy of the electron, , The probability of ionization after the step back can be made sufficiently close to 1. When ionization occurs, one electron becomes two electrons and one hole.
The two electrons drift in the bandgap gradient layer 201 toward the second step back, and the same phenomenon as described above occurs in the second step back. On the other hand, holes generated forward in the bandgap gradient layer 201 due to ionization drift forward in reverse to the electrons, and reach the first step back. If there is an energy step ΔEv in the valence band of the first step-back in which holes do not cause ionization in advance, the holes that have drifted ideally proceed forward as they are. If there is a positive energy step in front of the holes as shown in FIG. 44, the holes are scattered or accumulated at the step back, but ionization does not occur. In this way, electron drift, ionization, and hole drift repeatedly occur in each band gap gradient layer and step back,
The number of carriers will be multiplied. Eventually, the electrons multiplied by the ionization reach the N-type semiconductor layer, and as a current from the layer in ohmic contact with the N-type semiconductor layer, the holes reach the P-type semiconductor layer, and the P-type semiconductor layer. A hole current is extracted from the layer in ohmic contact with the layer.

By changing the composition ratio of the constituent materials as described above, a large number of semiconductor layers whose band gaps are continuously changed from a narrow side to a wide side are stacked, and a step back formed at that time is formed. By using the multi-layer heterojunction structure which promotes ionization by utilizing the above, it is possible to specify the place where ionization occurs as described above, make the probability of ionization as close to 1 as possible, and configure a low-noise APD.

[0018]

The element structure described above is one means for realizing a low-noise APD. However, in order to produce an element having such a structure, various elements are actually used. Subject to restrictions.

First, in order to obtain an element having a step-back structure layer capable of accelerating ionization as described above by changing only the composition ratio of the constituent material, the constituent material and the manufacturing method are limited. Will be done. For example, on a GaSb substrate of a III-V compound semiconductor,
AsSb / GaSb grown, InGaAl on InP substrate
As / InGaAs grown, InGaAsSb on GaSb substrate
/ GaSb grown, and II-V
Materials grown from HgCdTe, a group I compound semiconductor, can be cited as a material that can constitute an element having such a structure.

However, Ga, As, H
Since g and Cd are highly toxic and rare and expensive elements, they are problematic materials for industrial handling.

Further, all of them are prepared by a molecular beam epitaxy method (MBE method).
It requires an ultra-high vacuum, and the semiconductor growth rate is slow.
It is not suitable for increasing the area, and mass production has been difficult. Further, the MBE method requires a semiconductor growth temperature of typically 500
In the case where such a light receiving element is formed on a semiconductor device on which an integrated circuit or the like has already been formed, the light receiving element has a problem of causing some damage to the existing semiconductor device. doing.

Furthermore, in order to produce such a low-noise APD, it is necessary to change the composition ratio of these materials so that ionization always occurs at the step back. Lattice matching that does not cause trap levels at the junction interface,
In addition, it is necessary to determine the composition ratio of the material in consideration of the electron affinity having a step back energy step ΔE equal to or more than the ionization energy. As a result, the band gap of the APD that can be actually created is restricted.

For example, first, when the first material is used, according to an experiment, in the case of a lattice matching structure, the material (GaSb) having the narrowest band gap has a band gap of 0.73 eV.
Is the material with the widest band gap (Al _1.0 Ga _0.0 As
The band gap of _0.08 Sb _0.92 ) is 1.58 eV, and the maximum band gap difference is 0.72 eV on the conduction band side and 0.13 eV on the valence band side.
It has been confirmed that the eV and the electron ionization energy are 0.80 eV (GaSb). The shortage of 0.08 eV for the ionization energy of the electrons in the step back is supplied from the drift electric field of the electrons. By the way, in such an element, a leakage current (dark current) signal generated when light is not irradiated is apt to be generated, and this increases a noise component. Therefore, there is a big problem that noise cannot be reduced after all. I have. Causes of the occurrence of dark current include carriers injected from a layer (external electrode of the element) in ohmic contact and carriers thermally generated via a defect level, a heterointerface level, and the like inside the element. In such a device, the effect of blocking injected carriers is firstly brought out by providing the P-type semiconductor layer and the N-type semiconductor layer. However, conscious and sufficient consideration has been given to this point. However, this effect is not enough. The amount of thermally generated carriers depends on the density of defect states, the density of interface states, and the like, but essentially depends on the size of the band gap. It is known that the amount of generated carriers is reduced. However, such devices also have the disadvantage that the minimum band gap is too narrow to suppress thermally generated carriers. Semiconductor light-receiving devices having such a band gap are suitable for receiving light in the wavelength region of 1.0 μm to 1.6 μm, but are not suitable for light-receiving devices in other wavelength regions, for example, visible light receiving devices. Difficult, its application was limited.

Next, for example, in the second combination of materials, although the ionization energy is as large as about 1 eV, the conduction band energy step in the step back is as small as about 0.6 eV, which is not promising.

The other materials mentioned above have the same disadvantages as the original material. In particular, in the last combination of materials, for example, according to a paper by TP Pearsall published in Electronics Letters, 18th Edition, 12th (June, 1982), p.
By changing the composition ratio of Cd, a device having a minimum bandgap of 0.5 eV and a maximum bandgap of 1.3 eV has been proposed. It is easily affected by the generated dark current.

Therefore, in order to effectively put into practical use a low-noise APD having a structure for increasing the ionization ratio of carriers, a material, a degree of freedom in selecting a manufacturing method, a suppression of dark current, and a wide light receiving wavelength region are required. It is necessary to consider the band structure.

Also, when light is incident on the step-back structure layer, carriers may be generated in the step-back structure layer, and the multiplication factor may vary depending on the wavelength of the incident light. Was.

That is, the technical problems to be solved by the above-described APD are summarized as follows.

The technical problems relating to the performance of the element are as follows: (1) Since the incident light is absorbed by the p-type semiconductor layer and the multiplication layer, the multiplication factor changes depending on the incident wavelength of the light, making the element unsuitable as a reading element. It is. (2) Since the forbidden band width of the light absorption layer and the multiplication layer is small, dark current during operation is high and noise is large. (3) Since it is intended for optical communication, the material is limited, and the light that can be handled is about 800 to 1600 nm, and cannot be used for light of other wavelengths such as visible light.

The technical problems in device fabrication are as follows: (1) In order to form a step-back structure using a compound semiconductor, it is difficult to modulate the composition, and the energy steps ΔEc, ΔEc
There is a limit on the magnitude of Ev, and there is a limit on noise reduction. (2) Since it is made of a compound semiconductor belonging to the group III-V, II-VI, etc., it has problems as industrial materials such as toxicity and price of the material. (3) The method of forming a compound semiconductor has problems such as the necessity of ultra-high vacuum, the necessity of forming a film at a high temperature (about 500 to 650 ° C.), the difficulty of increasing the area, and the like. It is unsuitable as a method for manufacturing an element. And the like.

An object of the present invention is to solve the above-mentioned conventional technical problems and to provide excellent high-speed response, no variation in the multiplication factor due to the wavelength of incident light, stable multiplication characteristics, and On the other hand, it is an object of the present invention to provide a photoelectric conversion device having a novel configuration that has low noise, high sensitivity, easy area enlargement, and low noise.

Another object of the present invention is to provide a semiconductor light receiving element as a photoelectric conversion device having excellent characteristics in a wide light receiving wavelength region, particularly in a visible light wavelength region, in which dark current is suppressed, and in particular, a low noise avalanche photo diode. It is to provide a diode.

According to the present invention, there is provided a photoelectric conversion device having a light absorbing layer for absorbing incident light to generate carriers and a multiplication layer for multiplying the carriers. the light absorption between the multiplication layer and the light absorbing layer
Light transmitted through the Osamuso is provided shielding <br/> optical layer prevents incident on the multiplication layer Rutotomoni, unnecessary carriers before externally
To prevent injection into the light absorbing layer and the multiplication layer
A charge injection blocking layer is provided .

Further, the photoelectric conversion device of the present invention is a photoelectric conversion device having a light absorption layer for absorbing incident light to generate carriers and a multiplication layer for multiplying the carriers, wherein the first electrode A first charge injection blocking layer for preventing unnecessary carriers from being injected into the photoelectric conversion device from the first electrode, the multiplication layer, and light entering the multiplication layer. A light-blocking layer for preventing a change in multiplication factor, the light absorbing layer, and a second charge injection block for preventing unnecessary carriers from being injected into the photoelectric conversion device from the second electrode. And a light-transmitting second electrode in this order.

Further, the photoelectric conversion device of the present invention is a photoelectric conversion device for outputting electric signals generated by a plurality of photoelectric conversion units, comprising: a light absorption layer for absorbing incident light to generate carriers; A plurality of photoelectric conversion units having a light-shielding layer between a multiplication layer for multiplying the photoelectric conversion unit, a storage unit for storing electric signals generated by the plurality of photoelectric conversion units, and a plurality of the photoelectric conversion units. Scanning means for scanning the electric signal generated in the, having a signal output unit having at least one means selected from reading means for reading the electric signal generated in a plurality of the photoelectric conversion unit, the A plurality of photoelectric conversion units and the signal output unit are electrically connected. [Operation] Hereinafter, the structure of the photoelectric conversion device and the structure of the energy band of the present invention will be described with reference to FIGS.

FIG. 1 is a schematic sectional view showing the structure of a photoelectric conversion device according to the present invention. The light absorbing layer 405 independent of the multiplication layer and the light transmitted through the light absorption layer 405 40
3, a light-shielding layer 404 and a multiplication layer 4 for preventing light from entering
03, a plurality of step-back structure layers 411 and 41
2 and 413, the p-type semiconductor layer 4 serving as a charge injection blocking layer
06 and the n-type semiconductor layer 402 and the p-type semiconductor layer 4
06 and the electrode 407, the n-type semiconductor layer 402 and the electrode 401
Are electrically connected. Note that the p-type semiconductor layer 406 serving as the charge injection blocking layer may be a metal that forms a Schottky junction with an adjacent semiconductor layer, of course, for which a similar effect can be expected. Further, although the case where the number of the step-back structure layers is three is shown, the present invention is not limited to this.

FIG. 2 is a schematic energy band diagram of the photoelectric conversion device when there is no bias. FIG. 3 is a schematic energy band diagram when the reverse bias is applied to the photoelectric conversion device.

The operating principle of the multiplication mechanism called the avalanche effect is the same as that of the conventional example proposed by Capasso et al., But the photoelectric conversion device of the present invention particularly has the following operation. (1) Since the light shielding layer 404 is provided between the light absorption layer 405 independent of the multiplication layer 403 and the step-back layers 411 to 413 (multiplication layer 403), the light absorption layer is viewed from the light incident side. There is almost no light intrusion into the multiplication layer provided at the back, and the change in the multiplication factor due to the light penetration into the multiplication layer is extremely small. (2) Since the multiplication layer 403 is made of a non-single-crystal material, Δ
Ec is close to or larger than the ionization threshold energy, so that it becomes easy to form a step-back structure layer (ΔEv is large in the case of electron multiplication and in the case of hole multiplication), the location where ionization occurs can be specified, and the ionization can be specified. The probability of 1
, So that low noise and a sufficient gain can be obtained. (3) Light absorbing layer 405 of the photoelectric conversion device to which the present invention is applied
Further, since a non-single-crystal material can be used as a constituent material of the multiplication layer 403, it is desirable in terms of forming at a low temperature and increasing the area. Here, the non-single-crystal material is a polycrystalline material or an amorphous material, and the amorphous material includes a material having a so-called microcrystalline structure in its category. Specifically, amorphous silicon compensated by hydrogen and / or a halogen element (hereinafter referred to as a-Si (H, X)), amorphous silicon germanium (hereinafter referred to as a-SiGe (H, X)) , Amorphous silicon carbide (hereinafter referred to as a-SiC (H, X)), polycrystalline silicon, or the like.
X-ray diffraction images were added to the halo pattern, and Si [111] [220] [31
1] also includes amorphous silicon having crystallinity having a peak specified by each Miller index.

As described above, since the constituent material of the element is a non-single-crystal material, a low temperature (for example,
200-300 ° C) and easily made on large area substrates,
In addition, the control of the forbidden band can easily be performed with the composition modulation or the like.
The multiplication layer of the step-back structure can be relatively easily formed, and diffusion of atoms due to heat or the like is suppressed, and a relatively reliable step-back structure can be easily formed. Is done.

In particular, since the charge injection blocking layer can be made of a material having a relatively wide band gap and a non-single-crystal material such as amorphous silicon having high doping effect and high crystallinity, dark current is reduced. . (4) Since the degree of freedom in selecting a material for forming the light absorption layer is large, a material having a large light absorption coefficient (for example, hydrogenated amorphous silicon “a-Si: H”) can be used.
The thickness of the light absorption layer can be reduced, and the entire device can be reduced. (5) The degree of freedom also increases for the forbidden band width of the light absorbing layer for the same reason as in (3), so that a photoelectric conversion element with high sensitivity to incident light of various wavelengths can be configured. In particular, the light absorbing layer 405
By setting the forbidden band width Eg1 to the forbidden band width corresponding to the visible part light, the visible part light can have high sensitivity. (Example of embodiment) Hereinafter, an embodiment of the present invention will be described. [Light Absorbing Layer] The light absorbing layer in the present invention is provided on the light incident side of the multiplication layer and the light shielding layer, and absorbs incident light to generate photocarriers.

As a material of the light absorbing layer, for example, a-Si (H,
X), a-SiGe (H, X), a-SiC (H, X), a-SiGeC (H, X) and other amorphous semiconductor materials, μc-Si (H, X), μc-SiGe ( H, X), μc-SiC (H, X)
Microcrystalline semiconductor materials such as poly-Si, poly-SiGe, poly-SiC
A non-single-crystal semiconductor material such as a polycrystalline semiconductor material can be used.

In order to provide a photoelectric conversion device having high sensitivity to visible light, the forbidden band width Eg1 of the light absorbing layer of the present invention is set as follows.
Preferably 1.1 eV or more and 1.8 eV or less, more preferably 1.2 eV
It is desirable to be eV or more and 1.8 eVeV or less. In order to obtain high sensitivity to infrared light in addition to visible light, the forbidden band width Eg1 of the light absorbing layer is preferably 0.6 eV or more and 1.8 eV.
Below, it is more desirable to be 0.8 eV or more and 1.2 eV or less. Further, in order to obtain high sensitivity to ultraviolet light in addition to visible light, the forbidden band width Eg1 of the light absorbing layer 405 is preferably 1.1 eV or more and 3.2 eV or less, more preferably 1.2 eV or less.
It is desirable to be eV or more and 3.0 eV or less.

The characteristics and knowledge required for the light absorbing layer will be specifically described below.

The light absorption layer 405 has a band gap and a band gap for absorbing light incident on the photoelectric conversion device in all or a part of the light absorption layer and absorbing light in a wavelength region to be subjected to photoelectric conversion and performing photoelectric conversion. Having a thickness is desirable to generate a signal that is faithful to the intensity of the incident light. In general, in order to absorb light having a wavelength equal to or less than a certain wavelength λ, the semiconductor light receiving element has a band of Eg ≦ hc / λ = 1240 nm · eV / λ [nm], where h is Planck's constant and c is the light speed. It is known that a gap Eg must be provided. Generally, the ratio of the light absorbed from the surface of the light receiving layer (depth 0) to the depth t of the light receiving layer to the incident light, that is, the light absorptance is 1-exp, where α is the light absorption coefficient.
It is also known to be represented by (−αt). From these, in general, for example, a visible light wavelength region (light wavelength of about 400
When light is intended for light reception, almost all of the light, particularly light having a long wavelength of about 700 nm, which penetrates deeper into the element, is absorbed and photoelectrically converted in this light receiving region. Is that the band gap of the light receiving region of the semiconductor light receiving element as the photoelectric conversion element needs to be about 1.77 eV or less, and the thickness of the light receiving region is -1 / α 1n (1-p) is desirable. For example, specifically, when crystalline silicon is used for the light absorbing layer (light receiving region) of the semiconductor light receiving element, the wavelength 7
In order to absorb 90% of the incident light of 00 nm in this light receiving region and perform photoelectric conversion, an experimentally obtained typical value of the light absorption coefficient α of about 2 × 10 ³ cm ⁻¹ is used. The calculation yields the finding that a light absorbing layer thickness of about 1.15 μm is required. In addition, of the photocarriers (electrons and holes) generated by photoelectric conversion in the light absorbing layer, a carrier having a higher ionization rate is transported to the multiplication layer and starts drifting such that avalanche multiplication is started. It is desirable that an electric field or a diffusion electric field is generated in the light absorbing layer.

Further, the light absorbing layer which can be used in the present invention has a high bandgap of the light absorbing layer so as to have high sensitivity to light of a desired wavelength and efficiently cope with a wider range of wavelengths. Eg1 may be changed non-uniformly in the layer thickness direction.

For example, in order to form a light-absorbing layer having high sensitivity to the wavelength region of visible light to infrared light, the forbidden band width Eg1 of the light-absorbing layer is preferably set to Eg1 for obtaining high sensitivity to visible light. 'And the forbidden band width Eg1''(Eg1'> Eg1 '') for obtaining high sensitivity to infrared light and the aforementioned Eg
It is sufficient to provide a region where the forbidden band width is changed to 1 ′.
In order to form a light absorbing layer having high sensitivity to the wavelength region of visible light to ultraviolet light, the band gaps Eg1 'to Eg are similarly formed.
It is sufficient to provide a region that changes to 1 ″ ′ (Eg1 ′ <Eg1 ′ ″).

Here, the region where the forbidden band width changes is desirably disposed at the end of the light absorbing layer, and the forbidden band width continuously changes within the light absorbing layer so that good carrier mobility can be obtained. It is preferred in terms of.

In order to more efficiently absorb the incident light and generate photocarriers, the forbidden band width for the transmission and absorption of light is taken into consideration, and the forbidden band width is large on the incident side. It is desirable to arrange the forbidden band width on the opposite side.

The thickness of the light absorbing layer is preferably 20
It is preferable that the thickness is 0 ° or more and 10 μm or less, more preferably 2000 ° or more and 2 μm or less, in order to efficiently generate photocarriers by incident light. [Light-Shielding Layer] In the present invention, the light-shielding layer 404 is provided between the light-absorbing layer 405 and the multiplication layer 403, and a part of incident light has passed through the light-absorbing layer 405. This is a layer that prevents light from entering the multiplication layer.

By preventing light from being incident on the multiplication layer 403, generation of photocarriers in the multiplication layer 403 can be prevented. In particular, it is possible to prevent long wavelength light such as infrared light having a deep transmission depth among the wavelength components of the incident light from being absorbed in the vicinity of the minimum forbidden band width portion of the step-back layer, thereby preventing the gain from fluctuating. Further, a material having a narrow forbidden band width can be applied as a material of the multiplication layer without being limited to the cause of the above-mentioned fluctuation of the multiplication factor.

As a material that can be used as the light shielding layer 404 of the present invention, any material may be used as long as it does not hinder the movement of the photocarriers generated in the light absorbing layer 405 and prevents light from entering the multiplication layer. Examples of such a material include a material which is electrically conductive or semiconductive and has light reflection characteristics (high light reflectance) or a material having light absorption characteristics (high light absorption).

As a material constituting the light shielding layer, for example, C
r, Mg, Al, Ti, Mn, Fe, Cu, Zn, M
A work function that enables smooth transport of electrons from the light absorbing layer to the multiplier layer and transport of holes from the multiplier layer to the light absorbing layer such as o, Ag, Cd, In, Sn, W, and alloys thereof. The metal material having is preferably used.

The energy band when the light-shielding layer is formed of the above-mentioned metal material is different from the type shown in FIGS. 43 and 44, and is different from that shown in FIGS. 4 (no bias) and 5 (reverse bias application). Become.

Examples of other materials that can be used for the light shielding layer include a semiconductor material having an energy of an energy gap (forbidden band width) smaller than the energy of incident light.
This semiconductor material may be P-type or N-type. Examples of such materials include Si-based semiconductors doped with impurities (amorphous or crystalline Si, SiN and SiC, SiGe, S
iSn, etc.) and III-V and II-VI compound semiconductors (I
nP, GaAs) and the like.

As the impurities to be doped into the semiconductor layer used as the light-shielding layer, B, Al, In, Tl, etc.
Group atom, group IV atom such as P, As, Sb, Bi, Li,
Group I atoms such as Na and K, and Group II atoms such as Mg and Ca;
Group IV atoms such as Si and Ge are preferably used.

In the case where the semiconductor used as the light-shielding layer is doped with the above-described impurity, the impurity concentration is 1.0 × 10 5
¹⁵ atoms / cm ³ or more and 1.0 × 10 ²¹ atoms / cm ³ or less;
It is desirably 0 × 10 ¹⁶ atoms / cm ³ or more and 1.0 × 10 ¹⁷ atoms / cm ³ or less to prevent light transmitted through the light absorbing layer from entering the multiplication layer.

Other suitable materials that can be used as the light-shielding layer include a high-temperature superconducting material, a conductive ceramic material such as graphite, which can block incident light, and a conductive organic compound.

Further, a reflective layer for reflecting light transmitted through the light absorbing layer to the light absorbing layer side is further laminated on the layer made of the above-mentioned material exemplified as a material usable for the light shielding layer. The light-shielding layer may be formed. As a material of the reflection layer, a material having a high carrier mobility and a high refractive index is desirable. For example, a material having a higher refractive index than that of the light absorption layer can be used.

The layer thickness of the light-shielding layer must be sufficient to prevent light transmitted through the light-absorbing layer from being absorbed in the multiplication layer and to prevent generation of carriers that cause fluctuations in the multiplication factor. However, if the light-shielding layer is too thick, the traveling property (mobility) of the carrier is reduced. The thickness of the light-shielding layer of the present invention is preferably 50 ° or more and 10 µm or less, more preferably 1 µm or less.

When the reflective layer is provided, the apparent optical path length of the light passing through the light absorbing layer becomes longer, so that a thinner light absorbing layer can be used, and the thickness of the photoelectric conversion device can be further reduced. Can be. [Multiplier layer] The multiplier layer in the present invention is provided on the back side between the light absorbing layer and the light shielding layer when viewed from the light incident side, and when a photocarrier generated in the light absorbing layer is transported, a so-called avalanche is used. This is a layer that multiplies the carrier by an effect.

The multiplication layer according to the present invention has a region in which carriers drift and a region in which ionization occurs. For example, the multiplication layer may have a structure in which a layer having a high dielectric constant and a layer having a low dielectric constant are stacked. Alternatively, a step-back structure in which the forbidden bandwidths of the minimum forbidden bandwidth Eg2 and the maximum forbidden bandwidth Eg3 continuously change may be used.

In any case, since the location where ionization occurs in the multiplication layer can be specified, the generation of noise due to the fluctuation of the location where ionization occurs can be suppressed. First, a multiplication layer formed by laminating layers having different dielectric constants will be described.

The structure of a multiplication layer formed by laminating layers having different dielectric constants is basically only required that materials having a large dielectric constant and materials having a small dielectric constant are alternately arranged. As an example, an alloy material, one of the multi-component materials,
By changing the composition ratio, a layer having a large dielectric constant and a layer having a small dielectric constant may be formed.

For example, using amorphous silicon nitride Si _z N _{1 -z} (Z is a composition ratio), a Si _X N _{1 -X} layer (X is larger than 0.5) as a layer having a large dielectric constant, The avalanche region may be formed by alternately arranging Si _y N _1-y layers (y is smaller than 0.5) as layers having a small ratio.

The avalanche region may be made of, for example, amorphous silicon carbide in addition to the above-mentioned amorphous silicon nitride.
It is also possible to use a material such as Si _z C _1-z or amorphous silicon germanium Si _z Ge _1-z .

In addition, as a manufacturing method for producing the photoelectric conversion device of the present invention, a deposition method is generally easy, and a vapor deposition method, a chemical vapor deposition (CVD) method, a vapor phase epitaxy method, a sputtering method A deposition method such as molecular beam epitaxy or the like by vapor phase growth can be used. In addition, other than such a deposition method, an ion implantation method or the like may be used. That is, to form a layer having a small dielectric constant, ion implantation such as implantation of hydrogen, carbon, nitrogen or the like into silicon or implantation of hydrogen into gallium arsenide is also useful.

Examples of a material that can easily form a layer having a changed dielectric constant and band gap by changing its composition include an amorphous material and a III-V compound semiconductor material.

In particular, an amorphous material is more preferably produced by a glow discharge method. However, in producing an element having the structure of the present invention, the production temperature is low and an integrated circuit or the like is already formed. Can be stacked on a semiconductor device that can be made, a wide range of materials can be selected without much concern for lattice matching, a high degree of freedom can be achieved, and the composition change layer can only be changed by changing the flow ratio of the source gas. It has features such as being easily formed by the method, having high sensitivity to light in the visible light range, being able to use non-polluting industrial and inexpensive materials, and being able to easily form a large area film. Therefore, if this is used, all the conventional problems can be solved.

More specific examples of the amorphous material include, as base materials, tetrahydric silicon, chalcogenite selenium, etc., as well as silicon oxide, silicon nitride, silicon oxynitride,
Silicon carbide,... Can be used as a material for a layer having a different dielectric constant or a layer for changing a band gap. At this time, in order to form a band gap changing layer in which the localized level in the band gap is reduced, the amount of the band gap changing atom acting as a band gap adjusting agent is usually 0.01% or more, preferably 1%. It is preferably at least 60 atomic%, more preferably at least 5 atomic% and at most 35 atomic%.

In particular, using silicon atoms as a base material,
When the glow discharge method is used for the production method, the gaseous raw materials include SiH ₄ , SiF ₄ , Si ₂ H ₆ , Si ₂ F ₆ , Si ₃ H ₈ ,
Chain silane compounds such as SiH ₃ F, Si ₂ F ₂ or Si
_{5 H 10, Si 6 H 12} , Si 4 H 8 is a cyclic silane compound is useful such as, also, as the raw material gas to create a layer for changing a layer or band gap different dielectric constants, CH _4, CH ₂ F ₂ ,
Carbon compounds such as C ₂ H ₆ , C ₂ H ₄ , C ₂ H ₂ , Si (CH ₃ ) ₄ , SiH (CH ₃ ) ₃ , N ₂ , NH ₃ , H ₂ NNH ₂ , HN ₃ NH ₄ N ₃ , F ₃ N, F ₄ N and other nitrogen compounds, O ₂ , CO ₂ , NO, NO ₂ , N ₂ O, O ₃ , N ₂ O ₃ , N ₂ O ₄ , NO ₃ and other oxygen compounds, GeH ₄ Germanium compounds such as GeF ₄ and tin compounds such as SnH ₄ are useful.

As the film forming conditions, a range of well-known conditions for forming an a-Si based film can be used. For example,
The temperature of the substrate is 50 to 600 ° C., preferably 150 to 40 ° C.
0 ° C., discharge pressure 0.01 to 10 Torr, preferably
0.1-1 Torr, high frequency power 0.01-10 W / cm
² , preferably 0.1 to 1 W / cm ² . The discharge frequency is DC or AC, especially 13.56 MHz which is often used.
Alternatively, microwave such as 2.45 GHz can be used.

Further, an avalanche region (multiplication layer)
Used as a doping material for the blocking layer (charge injection blocking layer) described later,
Group III and V atoms are useful. Specifically, examples of Group III atoms include boron (B), aluminum (Al), Ga (gallium), In (indium), and Tl (thallium). Particularly preferred are: B and Ga. As group V, P (phosphorus), As
(Arsenic), Sb (antimony), Bi (bismuth) and the like, and particularly preferred are P, As, Sb
It is. The content of such atoms is preferably 5% or less, more preferably 1% or less.

As described above, when the bias voltage is applied, the multiplication layer having the energy band as shown in FIG. 6 generates an electric field that does not cause ionization of carriers. By alternately laminating the layers 21, 23, 25 and the second layers 22, 24 having a high dielectric constant that generates an electric field that promotes the ionization of carriers, the place where the ionization occurs can be specified.
Therefore, a low-noise APD in which the probability of ionization approaches 1 without limit can be realized.

Further, a multiplication layer having an energy band at the time of bias application as shown in FIG. 7 is also included as a multiplication layer of the photoelectric conversion device of the present invention. That is, the first layers 41, 43, and 45 having a low dielectric constant and the second layers having a high dielectric constant
Are alternately deposited, and the multiplication layer in which the band gap of the first layer and the band gap of the second layer have different sizes can also be suitably used in the present invention.

Here, the layer thickness l _{1 of} the first layer having a small dielectric constant
Is preferably 20 ° or more and 2000 ° or less, more preferably 50 ° or more and 200 ° or less.

The layer thickness l _{2 of} the second layer having a large dielectric constant is
Is preferably 30 ° or more and 3000 ° or less, more preferably 75 ° or more and 300 ° or less. The thickness ratio between the first layer and the second layer is preferably 1.5 times or more, more preferably 2 times or more.

Next, a multiplication layer having a step-back structure in which the forbidden band width of the minimum forbidden band width Eg2 and the maximum forbidden band width Eg3 continuously changes will be described.

The multiplication layer has at least one step-back structure in which the forbidden band width changes continuously as described above. Here, the number of the step-back structures may be determined according to a desired multiplication factor.

In order to form a layer having a step-back structure in which the forbidden band width is continuously changed (step-back layer), the composition of the main atoms forming the step-back layer may be changed.

For example, the forbidden band width can be changed by changing the content of Group III and Group V atoms in the periodic table III-V compound semiconductor.

As another example, in the case of an amorphous silicon alloy-based material, an atom such as a germanium atom or a carbon atom serving as a bandgap adjusting agent may be contained, and the content may be changed as desired. .

The maximum forbidden bandwidth Eg3 and the minimum forbidden bandwidth Eg2
The difference from this is sufficiently large for ionization to occur, and it is desirable to have a structure in which the step back shown in the energy band diagram changes steeply in order to identify the place where ionization occurs. However, even if the step back becomes gentle to some extent, it can be used as the multiplication layer of the present invention. When the step back is gentle, it is desirable that the width (layer thickness) of the slowly changing layer region is within the mean free path of electrons in the material of the layer region. Specifically, it is desirable that the angle be 100 ° or less, more preferably 50 ° or less.

The thickness of the step-back layer may be any thickness as long as the carrier can travel without recombination, and is preferably 50 ° or more and 1 μm or less, more preferably 200 ° or less.
It is desirable to set it to {not less than 1000}.

In the present invention, in order to increase the degree of freedom in selecting a material for forming the multiplication layer, an impurity which is sandwiched between step-back layers (graded band gap layers) having a step-back structure and controls conductivity is used. May be provided at a high concentration to shift the Fermi level.

The high-concentration impurity layer may have a single-layer structure or a multi-layer structure, or may contain impurities unevenly in the layer thickness direction.

In order to make the impurity non-uniformly contained in the layer, the impurity concentration in the inclined bandgap layer is continuously changed from the high-concentration impurity layer side toward the center, whereby the gradient bandgap is changed. In the step-back portion obtained by the bonding between the layers, even if the energy step of the band is insufficient with respect to the ionization energy of the carrier, the insufficient energy is supplemented, and the ionization of the carrier in the step-back portion is performed. It is possible to reduce noise by suppressing the fluctuation of the place where ionization occurs.

When a bias is applied to the gradient band gap layer beyond a bias required for carrier drift, ionization is reliably performed in the step-back portion, so that there is no change in bias and no change in multiplication factor due to temperature change. Therefore, as a driving method of the photoelectric conversion device, an operation of accumulating the optical signal carrier at one end of the photoelectric conversion device and reading the carrier can be performed. Also, there is no need for temperature compensation for the multiplication factor.

Further, since it is possible to manufacture a low-noise photoelectric conversion device using a material that does not provide energy necessary for ionizing carriers by using only the energy of the band difference generated by the difference in electron affinity, the material can be freely selected. The degree spreads.

The material used in the present invention is desirably a material whose composition can be freely changed and which can form a gradient band gap layer. The material of the high-concentration impurity layer uses the effect of the band profile in which the energy difference of the energy step of the band obtained at the junction between the inclined band gap layers and the ionization energy of the carrier is changed by the impurity addition. Must be a possible material. As a material satisfying such a condition, a non-single-crystal semiconductor material such as amorphous or polycrystalline is preferable.For example, hydrogenated amorphous silicon (a-Si: H) -based alloy, and III-V group or Group II-VI compound semiconductor materials. In amorphous silicon alloys, respectively, a-SiGe: H, a-SiC: H, a-SiN: H, a-SiSn: H, a-SiO: H,
And a-GeC: H. In the III-V group, Al.Ga.As.
Sb, In ・ As ・ Sb, InGaAsSb, In ・ Ga ・ Al ・ As, In ・ AsP ・ Sb,
There are InGaAsSb and AlGaP, etc., and in the II-VI group, ZnSSe, Zn
CdS, HgCdTe, etc. are used. In addition, in addition to hydrogen, the amorphous silicon alloy material further contains F, C
It may contain a halogen atom such as l, Br, I and the like. The impurities in the high-concentration impurity layer or the inclined band gap layer include the following. For amorphous silicon-based alloys, P-type control
For Group III atoms and N-type control, Group V atoms of the periodic table are used. Specifically, Group III atoms include:
B (boron), Al (aluminum), Ga (gallium), In
(Indium), Tl (thallium) and the like can be mentioned, and particularly preferable are B and Ga. Examples of Group V atoms include P (phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth), and particularly preferred are P and Sb.

The high-concentration impurity layer has a p-type on the wide band gap side and an n-type on the narrow band gap side when electrons are to be ionized like an amorphous silicon alloy. Is n-type on the wide band gap side and p-type on the narrow band gap side.

When the composition of the high-concentration impurity layer is on the wide gap side of the inclined band gap layer, it is necessary to determine the composition so that the band gap is not smaller than the band gap at the end of the wide band gap of the inclined band gap layer. In the case where the band gap is on the narrow gap side of the inclined band gap layer, the band gap should be determined so as not to be larger than the narrow band gap end of the inclined band gap layer.

Regarding the composition distribution of the high concentration impurity layer,
On the wide band gap side, when the band gap decreases from the step-back portion toward the wide gap end of the gradient band gap layer, the energy band gradient becomes gentler, and when the band gap increases, the energy band slope decreases at the conduction band side. Thus, the maximum value of the electron affinity difference and the sum of the electron affinity difference and the band gap difference on the valence band side cannot be used. On the narrow band gap side, when the band gap increases from the step back portion toward the narrow band gap end of the inclined band gap layer,
When the slope of the energy band becomes gentle and becomes small, the electron affinity difference on the conduction band side and the sum of the electron affinity difference and the band gap difference on the valence band side cannot be used at the maximum value in the stepback portion. For this reason, it is preferable that the composition of the high-concentration impurity layer be uniform so that the band gap becomes uniform.

Regarding the distribution of the impurity concentration in the high-concentration impurity layer, the maximum impurity concentration required to obtain the same effect becomes larger when the distribution is non-uniform than when the distribution has a uniform concentration. Considering the addition limit of impurities, the degree of freedom of material selection may be narrowed, so that a substantially uniform distribution is desirable.

When the high-concentration impurity layer has a high-concentration impurity-containing layer at both ends of the tilted bandgap layer, the sum of the thicknesses of the two high-concentration impurity-containing layers is d ₁ + d ₂ , and one end thereof has If only a high concentration impurity layer is provided, its thickness d
Is determined to be less than or equal to the average free path of the carrier.

The impurity concentration of the high-concentration impurity layer is set so that the voltage applied when the high-concentration impurity layer is completely depleted becomes larger than the energy that is insufficient for the ionization energy of the carrier in the step-back portion, as described later. Is determined. That is, the case where the high concentration impurity layer is provided in multiple layers between the inclined band gap layers and the case where the single layer is provided in the single layer is determined as follows. When two high-concentration impurity layers are provided between the inclined bandgap layers,

[0095]

(Equation 1) N ₁ and N ₂ are satisfied.

In the above formula, the suffixes 1 and 2 correspond to the wide band gap and the narrow band gap, respectively, ε ₁ and ε ₂ are the dielectric constant of the high concentration impurity layer, and N ₁ and N ₂ are Impurity concentration of high concentration impurity layer, χ ₁ , χ ₂
Is the electron affinity of the high concentration impurity layer, Eion is the ionization energy of the carrier, and d ₁ and d ₂ are the film thickness of the high concentration impurity layer determined above. However, the above equation is for electron current, and for hole current,

[0097]

(Equation 2) It is. Eg1 and Eg2 are the band gaps of the high concentration impurity layer. When the high concentration impurity layer is provided as a single layer between the inclined band gap layers,

[0098]

(Equation 3) It is decided by. In the above equation, ε is the dielectric constant of the high concentration impurity layer, N is the impurity concentration of the high concentration impurity layer, and d is the film thickness of the high concentration impurity layer determined above. However, the above equation is for electron current, and for hole current,

[0099]

(Equation 4) It is.

Here, it is assumed that the impurity concentration distribution in the high concentration impurity layer is uniform.

Regarding the profile of the impurity concentration in the inclined bandgap layer, when an irregular high-concentration impurity layer is provided at both ends of the inclined bandgap layer, the impurity concentration is continuously reduced from both ends toward the center. When a high concentration impurity layer is provided only at one end, the impurity concentration is continuously reduced from one end toward the center. The function of the change in the impurity concentration is not particularly limited, but it is desirable that the function changes gradually on the high concentration side and sharply on the low concentration side.

Here, specific materials and numerical values will be described by taking an amorphous silicon-based alloy as an example.

As a material, the band gap can be changed from 1.1 eV to about 2.5 eV by changing the composition of, for example, an alloy of Si, Ge, and C. However, as a region having no practical problem, It is considered that a graded bandgap layer is formed in a range of 1.2 eV to 2.2 eV. These materials have a band gap of 1.1 eV or more than that of crystalline silicon, and a band gap of 1.2 eV, which is a minimum bandgap for reducing dark current.
, And the composition ratio that gives the maximum of 2.2 eV is

[0104]

(Equation 5) And the flow rate ratio of the production gas is almost the same.

A-SiGe: H having a band gap of 1.2 eV
When a-SiC: H 2 having a band gap of 2.2 eV is compared with a state in which impurities are not added, a step ΔE of the band on the conduction band side is obtained.
c (| χ ₁ −χ ₂ |) is 0.9 eV, the energy step ΔEv of the band on the valence band side is 0.1 eV, and the band step on the conduction band where electrons having a large ionization coefficient are transported is the ionization energy. Because there is a shortage of about 0.3 V at a certain 1.2 eV, even if a repeated structure of a graded bandgap layer is made as it is,
It is insufficient to reliably cause ionization at the step-back portion, and it is expected that application of a high electric field will cause fluctuations in the ionization location.

For this reason, in order to ensure ionization at the step-back portion, it is desirable to provide a high-concentration impurity-containing layer at one end of the inclined band gap layer. It is desirable that the impurity amount in the impurity-containing layer has a distribution in which the impurity concentration decreases toward the center of the inclined bandgap layer.
For example, if the high-concentration impurity layer is a-SiC: H side, which is a wide-gap material having a tilt band gap, the P-type impurity B
Is added to shift the energy band to the higher energy side.

In an amorphous silicon-based alloy, the mean free path λ of electrons in the impurity layer is typically 50 ° or more and 100 ° or less. Therefore, the thickness of the high-concentration impurity layer is, for example, 50 ° or less. I do.

Energy shortage required for ionization Eion
− (Χ ₂ -χ ₁ ) is 0.3 eV in this example, so 0.3 V
The width of the depletion layer that spreads when the voltage is applied is not more than the mean free path. Actually, the voltage applied when the high concentration impurity layer is completely depleted may be 0.3 V or more.
The relative dielectric constant is about 6,

[0109]

(Equation 6) Should be fine. In order to achieve an impurity concentration of 8.0 × 10 ¹⁸ , B ₂ H ₆ should be 0.3 to 0.4% with respect to the source gases SiH ₄ and CH ₄ .
What is necessary is just to add. On the other hand, when a high-concentration impurity layer is provided on the a-SiGe: H side, an N-type impurity P is added.

The thickness of the high-concentration impurity layer is set to 50 °. The relative permittivity is about 16.

The impurity concentration may be N> 2.1 × 10 ¹⁹ (cm ⁻³ ). To realize an impurity concentration of 2.1 × 10 ¹⁹ , 0.8 to 1.0% of PH ₃ may be added to SiH ₄ and GeH ₄ .

Next, consider the case where there is a P-type high concentration impurity layer on the a-SiC: H side and an n-type high concentration impurity layer on the a-SiGe: H side. The thickness of each of the high concentration impurity layers is 25 °. If we add the same concentration of impurities,

[0113]

(Equation 7)

[0114]

(Equation 8) That is, V _D = V _D1 + V _D2 = 2.6 × 10 ⁻²⁰ × N> 0.3 V, and the impurity concentration may be 1.2 × 10 ¹⁹ or more. In order to achieve this impurity concentration, 0.5 to 0.
More than 6% of B ₂ H ₆ and PH ₃ are converted to SiH ₄ and CH ₄ , SiH ₄ and GeH _{4 respectively.}
May be added.

The high-concentration impurity layer which can be suitably used in the present invention has been described by taking an amorphous silicon alloy as an example. However, the high-concentration impurity layer which can be used in the present invention is not limited to the above-described example. .

The operation and effect when a high-concentration impurity layer is provided between the band gap gradient layers will be described more specifically with reference to the drawings.

FIGS. 8 and 9 show that a negative bias is applied to the hetero-junction and to the wide band gap side in order to observe the change in the energy band on the conduction band on the premise of multiplication of electrons.
FIG. 4 is an explanatory diagram showing a state when all layers are depleted.

Since the energy band is joined so that the Fermi level matches at the heterojunction, the energy band varies depending on the conductivity type.

The energy obtained by carriers (electrons) near the junction is the energy band (conduction band: ΔE) at the junction.
In addition to c), the energy obtained by accelerating the carriers by the electric field near the junction (in the figure, the intensity of the electric field is represented by the amount of bending of the energy band), that is, the mean free path of the carriers from the junction. Is the sum of the amount of bending of the energy band within the distance.

As shown by broken-line circles in FIGS. 8 and 9, when an impurity is added near the junction, the energy band bends intensified in accordance with the impurity concentration, and the energy obtained by the carrier near the junction is reduced. And increase the probability of ionization.

In the case of a junction of the same type semiconductor, as shown in FIG. 8, a strong electric field is generated on the wide gap side, but the electric field increases as the distance from the junction increases, so that the probability of ionization other than at the junction increases. Would.

On the other hand, in the junction of the odd-shaped semiconductors, as shown in FIG. 9, the electric field at the junction is the strongest, the ionization at the junction is promoted, and the fluctuation of the ionization location can be suppressed. That is, in the hetero junction formed by the junction of the band gap gradient layer, the p / n junction or the p / i junction or the i / n junction is formed with a wide gap / narrow gap.
In the step-back section, the insufficient energy for the ionization of the carrier can be supplemented, and the ionization of the carrier can be reliably performed. In the case of multiplication of holes, the reverse
A / p junction, an i / p junction, and an n / i junction are preferred.

FIGS. 10A and 10B are explanatory diagrams showing changes in the electric field intensity at the heterojunction when the distribution of the impurity concentration in the inclined band gap layer is different. 10A shows the electric field strength in the case of the step change of the electric charge, and FIG. 10B shows the electric field intensity in the case of the continuous (linear function) change of the electric charge. When the same electric field is generated at the junction, it is clear from the Poisson equation. In addition, when the impurity concentration gradually changes from the junction, the electric field intensity near the junction increases.
That is, by gradually changing the impurity concentration at the high-concentration impurity layer sides 64a and 64b of the inclined band gap layer 63 shown in FIG. 11, the probability of ionization at the junction is increased, and the electric field strength at a point away from the junction is increased. Is small, the probability of ionization can be reduced, and the fluctuation of the ionization location can be suppressed.

FIG. 12, FIG. 13, and FIG. 14 are conceptual diagrams in consideration of the band gap inclination at the hetero junction. FIG.
The solid line indicates the state in which the wide gap layer having the uniform impurity concentration shown in FIG. 13 is depleted, and the broken line indicates the state in which the wide gap side of the inclined band gap layer having the uniform impurity concentration shown in FIG. 14 is depleted.

As shown by the broken line in the figure, the tilted band causes the band to be bent more gently due to the reduction of the band gap, and in ionization, the energy may be reduced and the fluctuation may be increased. Therefore, as shown in FIG. 15, the end portions of the inclined bandgap layers 51, 53, 55
By arranging the layers 52, 54, 56 having substantially uniform band gap Egd as the high-concentration impurity layers 52, 54, 56, it is possible to suppress the fluctuation of the ionization place.

The energy band when a reverse bias is applied to the multiplication layer shown in FIG. 15 is as shown in FIG. 16, and the layers 52 ', 54', and 5 have substantially uniform band gaps.
The electric field strength of 6 ′ is a layer 51 ′ having a non-uniform band gap,
The electric field strength is larger than 53 'and 55'.

As described above, according to the present invention, the probability of carrier ionization is made closer to 1 in the step-back unit,
Fluctuation of the location where ionization occurs can be suppressed, and low noise can be realized. As a result, for example, it is possible to provide a low-noise APD with a high degree of freedom in material and manufacturing method, and to provide an APD in which dark current is suppressed. The electrode that may be used in the photoelectric conversion device [Electrode] The present invention, the electrode material is first disposed on the light incident side, it is desirable enough transmittance to light having a wavelength of photoelectric conversion is high, e.g., In ₂ O
₃ , a translucent conductive material such as SnO ₂ , ITO (In ₂ O ₃ + SnO ₂ ), Si-Pd-O, and Pd is desirable. Further, by further providing a current collecting electrode having a comb shape, a mesh shape, a grid shape, or the like on the translucent conductive material, the electric resistance can be further reduced.

The electrodes provided on the side opposite to the incident light side can be made of a usual conductive material. [Charge Injection Blocking Layer] The above-mentioned electrode does not act as a barrier in the traveling direction of carriers serving as signals taken out of the light absorbing layer or the multiplication layer, and forms an ohmic junction with the electrode. A charge injection blocking layer (blocking layer) having p-type or n-type conductivity that serves as a barrier to the traveling of dark current carriers in the direction opposite to the traveling direction may be provided.

By providing the charge injection blocking layer, unnecessary carrier injection from the electrode can be prevented, so that noise due to dark current can be further reduced.

The charge injection blocking layer can be formed of the same material as that of the light absorption layer or the multiplication layer and containing a material capable of controlling conductivity.

The thickness of the charge injection blocking layer is preferably 50 °
Not less than 2000 ° and not more than 100 °, more preferably not less than 100 °
It is desirable that the angle be 0 ° or less.

The amount of impurities contained in the charge injection blocking layer is used in order for the layer to have good ohmic junction and charge injection blocking ability.
^-4 S / cm or more, more preferably 10 ^-3 S / cm or more. [Bias voltage] The bias voltage applied when operating the photoelectric conversion device of the present invention can deplete at least the multiplication layer, and drift of carriers in the band gap gradient layer (step back layer) or the low electric field layer. Is applied so as to generate an electric field that does not cause ionization, but selectively causes ionization in the step-back region where the energy level in the multiplication layer changes rapidly when the bias is applied.

[0133]

Embodiments of the present invention will be described below in detail with reference to the drawings. Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1, 4, and 5. FIG.

FIG. 1 is a schematic vertical sectional structural view showing a first embodiment of the photoelectric conversion device of the present invention. The photoelectric conversion device shown in FIG. 1 includes a Cr electrode 401 and an n-type a-Si _1-x G having a thickness of about 500 ° for preventing hole injection from the electrode 401.
e _x: charge injection blocking layer 402 made of H, for performing carrier multiplication _{a-Si 1-x Ge x} : H~a-Si 1-y C y: by laminating a layer with varying composition of H A multiplication region 403, a light-shielding layer 404 made of Cr having a thickness of about 200 ° for preventing light from entering the multiplication region, and a-Si having a thickness of about 1 μm for absorbing light and generating carriers: A light absorption layer 405 made of H, a charge injection blocking layer 406 made of p-type a-Si: H having a thickness of about 100 ° for blocking electron injection from the electrode on the light incident side, and a transparent electrode 407 mainly containing indium oxide. have.

The Cr electrode 401, the light shielding layer 404, and the transparent electrode 407 are formed by EB evaporation, and the charge injection blocking layer 402,
The amorphous layers of the multiplication region 403, the light absorption layer 405, and the charge injection blocking layer 406 were formed by a plasma CVD method. The source gas at the time of forming the amorphous layer is supplied to the charge injection blocking layer 402.
SiH ₄ , GeH ₄ , PH ₃ , H ₂ , and the multiplication region 403 include SiH ₄ , GeH ₄ , C
H ₄ and H ₂ , SiH ₄ and H ₂ were used for the light absorption layer 405, and SiH ₄ , B ₂ H ₆ and H ₂ were used for the charge injection blocking layer 406.

The multiplication region 403 includes CH ₄ and Ge of the source gas.
It was formed of three layers of composition change layers 411, 412, and 413 each having a thickness of 200 ° and a H ₄ gas flow rate continuously changed.

The energy band structure of the photoelectric conversion device of the first embodiment shown in FIG. 1 is ideally as shown in FIGS.

FIG. 4 is an energy band diagram when the photoelectric conversion device of the first embodiment is in a non-biased state, and FIG. 5 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. .

FIGS. 4 and 5 show the n-type a-Si _1-x Ge _x : H layer 4.
The forbidden band width of 02 is Eg4, a-Si _1-x Ge _x : H to a-Si _1-y C _y : H
The minimum forbidden band width of the multiplication region 403 composed of three layers of the composition change layers 411, 412, and 413 is Eg2, and the multiplication region 40
3 indicates that the maximum forbidden band width is Eg3, the forbidden band width of the a-Si: H layer 405 is Eg1, and the forbidden band width of the p-type a-Si: H layer 406 is Eg0. Reference numeral 404 corresponds to a Cr electrode.

In FIG. 4, there is a discontinuity in energy at both the conduction band edge and the valence band edge. In the state where the bias voltage is applied, as can be seen from FIG. Has almost no barrier due to energy discontinuity and does not hinder the traveling properties of carriers.

The composition change layers 411, 41 prepared here
The layer giving the maximum bandgap Eg3 of 2,413 is C
A-Si _1-y C _y : H having a composition ratio y of about 0.4, and Eg3 of about 2.
3 eV.

Further, a-Si _1-x Ge _x : Ge composition ratio x of H layer 402
Was about 0.6 and the forbidden band width Eg4 was about 1.3 eV.
Among the composition change layers 411, 412, and 413, the layer giving the minimum forbidden band width Eg2 was also an a-Si _1-x Ge _x : H layer, and Eg2 was also about 1.3 eV. The forbidden band widths Eg1 and Eg0 of the a-Si: H layers 405 and 406 were both about 1.8 eV.

The light absorption coefficient of the light absorption layer 405 is
About 1 × 10 ⁵ cm with respect to 400nm light ^{- 1,} is about 5 × 10 ³ cm ^-1 or more for light of wavelength 700 nm, absorption of visible portion light was sufficiently performed.

The multiplication factor of this apparatus was about 10 times or more when a bias of 10 V was applied. Also, for visible light having a wavelength of 700 nm or less, there was no change in the gain even when the wavelength was changed. Furthermore, the leakage current in the dark was as low as about 1 nA / cm ² or less when a bias of 10 V was applied. Furthermore, the optical response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 502, and was high. Embodiment 2 Hereinafter, a second embodiment of the present invention will be described with reference to FIGS.

FIG. 17 and FIG. 18 are energy band structure diagrams which are ideally assumed according to the second embodiment of the present invention.

FIG. 17 is an energy band diagram when the photoelectric conversion device of the second embodiment is in a non-biased state, and FIG. 18 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. It is.

The photoelectric conversion device shown in FIG. 17 is an n-type a-Si ₁ -yC _y : H layer 601 having a forbidden band width Eg 4 ′.
It is the same as FIG. 4 except that it is a p-type a-Si _1-y C _y : H layer 605 having a forbidden band width Eg0 ′. In the present embodiment, a-
Si _1-x Ge _x : H to a-Si _1-y C _y : H Composition change layers 611, 612
613 indicates that the minimum bandgap of the multiplication region 602 having three layers is Eg2, the maximum bandgap is Eg3, and the bandgap of the a-Si: H layer 604 is Eg1.

The multiplication factor of this apparatus was about 10 times or more when a bias of 10 V was applied. Further, even when the wavelength was changed for light having a wavelength of 700 nm or less, there was no change in the multiplication factor. Furthermore, the leakage current in darkness is about 0.
It was as low as 1 nA / cm ² or less. Furthermore, the light response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 602, and was high. (Embodiment 3) This embodiment is an embodiment in which the photoelectric conversion device shown in Embodiment 1 is stacked on a scanning circuit and a reading circuit which the present inventors have already applied for in Japanese Patent Application Laid-Open No. 63-278269. is there.

FIG. 19 is a schematic sectional view of the vicinity of the light receiving section according to the embodiment of the present invention, FIG. 20 is an equivalent circuit diagram of one pixel, and FIG. 21 is an equivalent circuit and a block circuit diagram of the entire device.

In the device shown in FIG. 19, an n ^- layer 702 serving as a collector region is formed on an n-type silicon substrate 701 by epitaxial growth, and a p base region 7 is formed therein.
03, and further an n ⁺ emitter region 704 is formed to constitute a bipolar transistor.

The p base region 703 is separated from an adjacent pixel, and a gate electrode 706 is formed between the p base region 703 and a horizontally adjacent p base region with an oxide film 705 interposed therebetween. Therefore, a p-channel MOS transistor is formed using the adjacent p base region 703 as a source / drain region. Gate electrode 706 also functions as a capacitor for controlling the potential of p base region 703.

After forming the insulating layer 707, an emitter electrode 708 and a base electrode 708 'were formed.

After that, an insulating layer 709 was formed, followed by an electrode 711, which was separated for each pixel. The electrode 711 is electrically connected to the electrode 708 '. Furthermore, n-type aS
An i _1-x Ge _x : H layer 712 was formed and separated for each pixel.

Subsequently, composition change layers 721, 722, and 723 of a-Si _1-x G _x : H to a-Si _1-y C _y : H are formed in the same manner as in the first embodiment to form a multiplication region. 713. Next, a Cr electrode (light shielding layer) 714 was formed and separated for each pixel. Next, a light absorption layer a-Si: H layer 715 was formed, a p-type a-Si: H layer 716 was formed, and a transparent electrode 717 for applying a bias voltage to the sensor was formed. Also, the collector electrode 718 is
01 is connected ohmic to the back surface.

Therefore, as shown in FIG. 20, the equivalent circuit of one pixel is provided with a p-channel MOS transistor 732, a capacitor 733, and a photoelectric conversion device 734 similar to that of the first embodiment on the base of a bipolar transistor 731 made of crystalline silicon. A terminal 735 for applying a potential to the base and a p-channel MOS transistor 73
2 and a terminal 736 for driving the capacitor 733
, A sensor electrode 737, an emitter electrode 738, and a collector electrode 739.

FIG. 21 is a circuit diagram in which one pixel cell 740 shown in FIGS. 19 and 20 is arranged in a 3 × 3 two-dimensional matrix.

In FIG. 21, the collector electrode 741 of one pixel cell 740 is provided for all pixels, and the sensor electrode 742 is also provided for all pixels. Also, PM
The gate electrode and the capacitor electrode of the OS transistor are connected to drive wirings 743, 743 ', and 743 "for each row, and are connected to a vertical shift transistor (VSR) 744. The emitter electrode is used for reading a signal for each column. It is connected to vertical wirings 746, 746 ', 746 ". The vertical wirings 746, 746 'and 746 "are switches 747 and 7 for resetting the electric charge of the vertical wiring, respectively.
47 ', 747 "and readout switches 750, 750',
750 ". The reset switch 747,
Gate electrodes 747 ′ and 747 ″ are commonly connected to a terminal 748 for applying a vertical line reset pulse, and a source electrode is commonly connected to a terminal 749 for applying a vertical line reset voltage. The gate electrodes of 750, 750 ', and 750 "are connected to a horizontal shift register (HSR) 752 via wirings 751, 751', and 751", respectively, and the drain electrodes are output amplifiers 757 through horizontal reading wirings 753. The horizontal read wiring 753 is connected to a switch 754 for resetting the electric charge of the horizontal read wiring.

The reset switch 754 is connected to a terminal 755 for applying a horizontal wiring reset pulse and a terminal 756 for applying a horizontal wiring reset voltage.

Finally, the output of the amplifier 757 is taken out from the terminal 758.

The operation will be briefly described with reference to FIGS. 19, 20 and 21.

The incident light is absorbed by the light absorption layer 715 in FIG. 19, and the generated carriers are multiplied by the multiplication region 713 and accumulated in the base region 703.

When a drive pulse output from the vertical shift register shown in FIG. 21 appears on the drive wiring 743, the base potential rises via a capacitor, and signal charges corresponding to the amount of light are supplied from the pixels in the first row to the vertical wiring 746, 746 ', 74
6 ". Next, scan pulses 751, 751 ', and 751" are output from the horizontal shift register 752.
750, 750 ', 75
0 ″ is sequentially controlled ON and OFF, and the signal is
Through the output terminal 758. At this time, the reset switch 754 is set to the switches 750, 750 ', 75
0 ″ is turned on during the ON operation in order to remove the residual charges of the horizontal wiring 753.

Next, the vertical line reset switch 747,
747 ′ and 747 ″ are turned on, and the vertical wiring 74
6, 746 ', 746 "are removed. When a pulse in the negative direction is applied from the vertical shift register 744 to the drive wiring 743, the PMOS transistor of each pixel in the first row is turned on, and each pixel is turned on. The base residual charge is removed and initialized.

Next, the drive pulse output from the vertical shift register 744 appears on the drive wiring 743 ', and the signal charges of the pixels in the second row are similarly extracted.

Next, extraction of signal charges from the pixels in the third row is performed in the same manner.

The apparatus operates by repeating the above operations.

In the embodiments described above, examples of the circuit according to the invention of the present inventors have been described, but a general photoelectric conversion device may be used.

The case where the photoelectric conversion device of the present invention is used for a photoelectric conversion device having a general configuration will be described below.

FIG. 22 is a block diagram showing a configuration in a case where the present invention is applied to a photoelectric conversion device having a general configuration.

In the figure, reference numeral 801 denotes a plurality of photoelectric conversion units according to the present invention. For example, the photoelectric conversion devices of the present invention shown in Embodiments 1 and 2 are used. Photoelectric conversion unit 80
1 is connected to the signal output unit 805. Signal output unit 805
802, a means for accumulating signal charges generated by the photoelectric conversion unit 801; a scanning means 803 for scanning the aforementioned signal charges; and a reading means 804 for amplifying the signal charges transferred by the scanning means 803 and comprising a noise compensation circuit and the like. Means. Note that the storage unit 802 is required when performing a storage operation, but need not be provided.

As described above, according to the photoelectric conversion device of this embodiment, the light absorption layer having a forbidden band width of Eg1 and absorbing light, the metal light shielding layer, and the carrier generated by absorbing light are provided. Band gap Eg2 and maximum band gap Eg3 that multiply
Layer having a step-back structure in which the forbidden band width changes continuously or a layer in which a multiplication layer formed by laminating a plurality of layers is sequentially laminated so as to be sandwiched between the charge injection blocking layers. In addition, various problems caused by band mismatch are solved, and a high-speed response similar to that of a photodiode having no multiplication layer is obtained, and at the same time, light incident from the light absorbing layer side is transmitted through the light absorbing layer. However, since the metal light-shielding layer shields light, the light does not enter the multiplication layer, and fluctuations in the multiplication factor due to light incidence can be eliminated.

Further, by setting the forbidden band width Eg1 of the light absorbing layer to various sizes, it was possible to give high sensitivity not only to visible light but also to light of various wavelengths.

Further, by selecting the number of layers of the step-back structure, an amplification factor of 2 or more was obtained and the noise was reduced.

The light absorption layer, the multiplication layer, and the charge injection blocking layer of the photoelectric conversion device of the present invention are made of a non-single-crystal material such as a polycrystalline material containing at least Si atoms or an amorphous material. The easy control of the forbidden band width and the low-temperature lamination were enabled, and various problems caused by the lamination could be solved. Embodiment 4 Hereinafter, a fourth embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3. FIG.

FIG. 1 is a schematic vertical sectional view showing a fourth embodiment of the photoelectric conversion device of the present invention. The photoelectric conversion device shown in FIG. 1 includes a Cr electrode 401, a charge injection blocking layer 402 made of n-type a-Si _1-x Ge _x : H having a thickness of about 500 ° for blocking hole injection, and a carrier multiplication. A-Si _1-X Ge _X : H ~
a-Si _1-y C _y : A multiplication region 403 in which the composition of H is changed, n for preventing light from entering the multiplication region and for enhancing the internal electric field of the light absorption layer to improve the traveling of carriers. Type a-Si _1-x Ge _x : H
A light absorption layer 405 made of a-Si: H having a thickness of about 2 μm for absorbing light and generating carriers, and a p-type a-Si: H having a thickness of about 100 ° for stopping electron injection. And a transparent electrode 407 mainly composed of indium oxide.

The Cr electrode 401 and the transparent electrode 407 are formed by EB evaporation, and the charge injection blocking layer 402, the multiplication region 403,
The amorphous layers of the n-type a-Si _1-x Ge _x : H layer 404, the light absorption layer 405, and the charge injection blocking layer 406 were formed by a plasma CVD method. The source gas for forming the amorphous layer is that the charge injection blocking layer 402 and the n-type a-Si _1-x Ge _x : H layer 404 are SiH ₄ , GeH ₄ , PH ₃ ,
H ₂ , the multiplication region 403 is SiH ₄ , GeH ₄ , CH ₄ , H ₂ , the light absorbing layer 40
5 used SiH ₄ , H ₂ , and the charge injection blocking layer 406 used SiH ₄ , B ₂ H ₆ , H ₂ .

The multiplication region 403 is composed of CH ₄ and Ge of the source gas.
It is composed of three layers of composition change layers 411, 412, and 413 each having a thickness of 200 ° and a H ₄ gas flow rate continuously changed. The gas flow rate of PH _{3 in} the n-type a-Si _1-x Ge _x : H layer 404 is slightly smaller than that in the charge injection blocking layer 402.

The energy band structure of the photoelectric conversion device of the fourth embodiment shown in FIG. 1 is ideally as shown in FIGS.

FIG. 2 is an energy band diagram when the photoelectric conversion device of the fourth embodiment is in a non-biased state, and FIG. 3 is an energy band diagram when a bias is applied to perform a carrier multiplication operation. is there.

FIGS. 2 and 3 show an n-type a-Si _1-x Ge _x : H layer 40.
2 of band gap _{Eg4, a-Si 1-X} Ge X: H~a-Si 1-y C y: minimum forbidden in multiplication region 403 consisting of three layers of H composition change layers 411, 412, 413 Band width is Eg2, multiplication area 403
Has the maximum forbidden band width of Eg3, the forbidden band width of the n-type a-Si _1-x Ge _x : H layer 404 is Eg5, and the forbidden band width of the a-Si: H layer 405 is Eg.
1, indicating that the forbidden band width of the p-type a-Si: H layer 406 is Eg0.

In FIG. 2, there are energy discontinuities at both the conduction band edge and the valence band edge. In the state where the bias voltage is applied, as can be seen from FIG. Has almost no barrier due to energy discontinuity and does not hinder the traveling properties of carriers.

The composition change layers 411, 41 prepared here
The layer giving the maximum bandgap Eg3 of 2,413 is C
A-Si _1-y C _y : H with a composition ratio y of about 0.4, and Eg3 of about 2.
3 eV.

The a-Si _1-x Ge _x : H layer 402 and the n-type a-Si
The Ge composition ratio x of the _1-x Ge _x : H layer 404 was about 0.6, and the forbidden band width Eg4 was about 1.3 eV. Composition change layers 411, 41
The layer giving the minimum band gap Eg2 of 2,413 is also a-
It was a Si _1-x Ge _x : H layer, and Eg2 was also about 1.3 eV. 40
The forbidden band widths Eg1 and Eg0 of the 5,406 a-Si: H layers were both about 1.8 eV.

The light absorption coefficient of the light absorbing layer (light shielding layer) 404 is about 1 × 10 ⁵ cm ⁻¹ or more with respect to light having a wavelength of 400 nm.
About 5 × 10 ³ cm ⁻¹ or more for light with a wavelength of 700 nm;
The visible light is sufficiently absorbed.

The multiplication factor of this apparatus was about 10 times or more when a bias of 10 V was applied. Also, for light having a wavelength of 700 nm or less, there was no change in the multiplication factor even when the wavelength was changed. Furthermore, the leakage current in darkness is about 1 when a bias of 10 V is applied.
It was as low as nA / cm ² or less. Furthermore, the light response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 403, and was high. Embodiment 5 Hereinafter, a fifth embodiment of the present invention will be described with reference to FIGS. FIGS. 23 and 24 are energy band structure diagrams of an ideally assumed fifth embodiment of the present invention.

FIG. 23 is an energy band diagram when the photoelectric conversion device according to the fifth embodiment is in an unbiased state. FIG. 24 is an energy band diagram when a bias is applied to perform the carrier multiplication operation.

In FIG. 23, reference numeral 601 denotes an n-type a-Si ₁ -yC _y : H layer having a forbidden band width Eg4 ′, and 605 denotes a forbidden band width Eg.
2 except that it is a p-type a-Si _1-y C _y : H layer of g0 ′ and an n-type a-Si: H layer of 603 is a forbidden band width Eg5 ′.
It is the same _{as, a-Si 1-X Ge} X: H~a-Si 1-y C y: multiplication region 602 consisting of three layers of H composition change layers 611, 612, 613
Has a minimum forbidden bandwidth of Eg2 and a maximum forbidden bandwidth of Eg3, aS
i: The forbidden band width of the H layer 604 is Eg1.

The multiplication factor of this apparatus was about 10 times or more when a bias of 10 V was applied. Further, even when the wavelength was changed for light having a wavelength of 700 nm or less, the gain did not change. Further, the leakage current in darkness is about 0.1 when a bias of 10 V is applied.
It was as low as nA / cm ² or less. Furthermore, the light response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 602, and was high. (Example 6) In this example, the photoelectric conversion device shown in Example 3 was produced in the same manner except that an n-type semiconductor layer was used as a light shielding layer instead of a metal light shielding layer.

FIG. 19 is a schematic sectional view of the vicinity of the light receiving section according to the embodiment of the present invention, FIG. 20 is an equivalent circuit diagram of one pixel, and FIG. 21 is an equivalent circuit and block circuit diagram of the entire device.

First, a base circuit substrate having a transistor was formed in the same manner as in Example 3.

[0191] _{Then, a-Si 1-X Ge} X: H~a-Si 1-y C y: multiplication region 7 to form a composition change layer 721 in H
13. Next, instead of the metal light-shielding layer of Example 3,
An n-type a-Si _1-X Ge _X : H layer 714 is formed and separated for each pixel, a light absorption layer a-Si: H layer 715 is formed, and a p-type a-Si: H layer 7 is formed.
16, and a transparent electrode 717 for applying a bias voltage to the sensor was formed.

A collector electrode 718 is ohmically connected to the back surface of the substrate 701. Therefore, in the equivalent circuit of one pixel, as shown in FIG. 20, a p-channel MOS transistor 732, a capacitor 733, and a photoelectric conversion device 734 similar to the fourth embodiment are connected to the base of a bipolar transistor 731 made of crystalline silicon. A terminal 735 for applying a potential to the base;
A terminal 736 for driving the OS transistor 732 and the capacitor 733, a sensor electrode 737, an emitter electrode 738, and a collector electrode 739 are provided.

FIG. 21 is a circuit diagram in which one pixel cell 740 shown in FIGS. 19 and 20 is arranged in a 3 × 3 two-dimensional matrix.

Since the operation is the same as that of the third embodiment, the description of the operation is omitted.

According to the photoelectric conversion device of this embodiment, Eg1
A light absorbing layer having a forbidden band width and absorbing light; an n-conductivity type layer having a forbidden band width of Eg5; a minimum forbidden band width Eg2 for multiplying carriers generated by absorbing light; Eg3
A layer formed by sequentially laminating a plurality of layers having a step-back structure in which the forbidden band width is continuously changed and a multiplication layer formed by laminating the layers is sandwiched between the charge injection blocking layers. Since the n-conductivity type layer interposed between the absorption layer and the multiplication layer functions as a reverse bias layer, carriers generated in the light absorption layer are smoothly transported, and the high speed is the same as that of a photodiode without a multiplication layer. Responsiveness is obtained. Further, by reducing the forbidden band width of the n-conductivity type layer provided between the light absorption layer and the multiplication layer, light incidence on the multiplication layer is reduced, so that fluctuation of the multiplication factor can be suppressed. Was.

In this example, the visible light was made to have high sensitivity by setting the forbidden band width Eg1 of the light absorbing layer to the forbidden band width particularly corresponding to the visible light.

Further, the components such as the light absorption layer, the n-conductivity type layer, the multiplication layer, and the charge injection blocking layer of the photoelectric conversion device of this embodiment are made of a non-single-crystal material containing at least Si atoms. Thus, easy control of the forbidden band width and low-temperature lamination are possible, and various problems caused by lamination can be solved. Seventh Embodiment Hereinafter, a seventh embodiment of the present invention will be described with reference to FIGS. 1, 25, and 26. FIG. 1 is a schematic longitudinal sectional structural view showing a seventh embodiment of the photoelectric conversion device of the present invention.

The photoelectric conversion device shown in FIG.
1. A 500-nm thick n-type a-
The charge injection blocking layer 402 made of Si _1-x Ge _x : H, and the composition of a-Si _1-X Ge _X : H to a-Si _1-y C _y : H for carrier multiplication was changed. A multiplication region 403, an a-Si _1-X Ge _X : H layer (light-shielding layer) 404 for preventing light from entering the multiplication region and increasing the internal electric field of the light absorption layer to improve the traveling of carriers. A-Si with a thickness of about 1μm for absorbing light and generating carriers
_1-X Ge _X: the light-absorbing layer 405 made of H, a thickness of about 100Å for blocking electron injection p-type _{a-Si 1-X Ge X} : charge injection blocking layer 406 made of H, mainly indium oxide Transparent electrode 407.

The Cr electrode 401 and the transparent electrode 407 are formed by EB evaporation, and the charge injection blocking layer 402, the multiplication region 403,
The amorphous layers of the a-Si _1-X Ge _X : H layer 404, the light absorption layer 405, and the charge injection blocking layer 406 were formed by a plasma CVD method. The source gas for forming the amorphous layer is the charge injection blocking layer 4
02 and a-Si _{1 -X} Ge _X : H layer 404 is SiH ₄ , GeH ₄ , PH ₃ , H ₂ , multiplication region 403 is SiH ₄ , GeH ₄ , CH ₄ , H ₂ , and light absorbing layer 405 is Si
H ₄ , GeH ₄ , H ₂ , the charge injection blocking layer 406 is made of SiH ₄ , GeH ₂ , B ₂ H ₆ , H
₂ was used.

The multiplication region 403 is composed of CH ₄ and Ge of the source gas.
It is composed of three layers of composition change layers 411, 412 and 413 having a thickness of about 200 ° and a gas flow of H ₄ continuously changed. The gas flow rate of PH _{3 in} the a-Si _{1 -X} Ge _X : H layer (light-shielding layer) 404 is slightly smaller than that in the charge injection blocking layer 402.

The energy band structure of the photoelectric conversion device of the seventh embodiment shown in FIG. 1 is ideally assumed to be as shown in FIGS. 25 and 26.

FIG. 25 is an energy band diagram when the photoelectric conversion device of the seventh embodiment is in a non-biased state, and FIG. 26 is an energy band diagram when a bias is applied to perform the carrier multiplying operation. is there.

FIGS. 25 and 26 show that the forbidden band width of the n-type a-Si _1-x Ge _x : H layer 501 is Eg4, and a-Si _{1 -X} Ge _X : H to a-Si _{1 -y} C _y. :
H The minimum forbidden band width of the multiplication region 502 composed of three layers of the composition change layers 511, 512, and 513 is Eg2, and the multiplication region 5
02 has a maximum forbidden band width of Eg3 and an n-type a-Si _1-X Ge _X : H layer 50
3, the forbidden bandwidth of the a-Si _{1 -X} Ge _X : H layer 504 is Eg 1, and the forbidden bandwidth of the p-type a-Si _{1 -X} Ge _X : H layer 505 is E
g0. Particularly, in this embodiment, Eg1
And Eg5 were set to have substantially the same value.

In FIG. 25, there are energy discontinuities at both the conduction band edge and the valence band edge. However, in the state where the bias voltage is applied, as can be seen from FIG. Has almost no barrier due to energy discontinuity and does not hinder the traveling properties of carriers.

The composition change layers 511, 51 prepared here
The layer giving the maximum forbidden band width of Eg3 of 2,513 is a-Si _1-y C _y : H having a C composition ratio y of about 0.4, and Eg3 is about
2.3 eV.

Further, a-Si _1-x Ge _x : H layers 501, 503, 5
The Ge composition ratio x of 04,505 is about 0.6, and the forbidden band width E
g4, Eg1 and Eg0 were both about 1.3 eV. Minimum forbidden band width Eg of the composition change layers 511, 512, and 513
2 is also an a-Si _1-x Ge _x : H layer, and Eg2 is also about 1.3 e.
V.

The light absorption coefficient of the light absorption layer 503 is the wavelength
About 1 × 10 relative to 800 nm of the light ⁵ cm ^{- 1} or more, wavelength 1000nm
Is about 2 × 10 ⁴ cm ⁻¹ or more, and infrared light can be sufficiently absorbed.

The multiplication factor of this apparatus was about 10 times or more when a bias of 10 V was applied. Also, for light having a wavelength of 1000 nm or less, there was no change in the gain even when the wavelength was changed. Furthermore, the leakage current in darkness is about 1 when a bias of 10 V is applied.
It was as low as 0 nA / cm ² or less. Furthermore, the optical response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 502, and was high. Embodiment 8 Hereinafter, an eighth embodiment of the present invention will be described with reference to FIGS. FIG. 27 and FIG. 28 are diagrams of an energy band structure which is ideally assumed according to the eighth embodiment of the present invention.

FIG. 27 is an energy band diagram when the photoelectric conversion device of the eighth embodiment is in a non-biased state, and FIG. 28 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. It is.

In FIG. 27, an n-type a-Si ₁ -yC _y : H layer 60 having a forbidden band width Eg4 ′ in which the charge injection blocking layer has a wide gap is provided.
1 except that it is 1. a-Si _1-X Ge _X : H
~ A-Si _1-y C _y : H 3 of composition change layers 611, 612, 613
The minimum bandgap of the multiplication region 602 composed of layers is Eg2, the maximum bandgap is Eg3, and the n-type a-Si _1-X Ge _X : the bandgap of the H layer 603 is Eg5, a-Si _1-X Ge _X : The forbidden band width of the H layer 604 is Eg
1, indicating that the forbidden band width of the p-type a-Si _1-x Ge _x : H layer 605 is Eg0.

The multiplication factor of this apparatus was about 10 times or more when a bias of 10 V was applied. Further, even if the wavelength was changed with respect to infrared light having a wavelength of 1000 nm or less, there was no change in the multiplication factor due to the penetration of light into the multiplication layer. Further, the leakage current in the dark was as low as about 10 nA / cm ² or less when a bias of 10 V was applied. Furthermore, the photoresponse speed is a pin without the multiplication layer 602.
It was equivalent to a high-speed photoelectric conversion device and was high speed. (Example 9) In this example, a photoelectric conversion device was formed in the same manner as in Example 6, except that the light absorption layer of the photoelectric conversion device shown in Example 6 was replaced with the light absorption layer of Example 7. is there.

FIG. 19 is a schematic sectional view showing the vicinity of the light receiving section according to the embodiment of the present invention, FIG. 20 is an equivalent circuit diagram of one pixel, and FIG. 21 is an equivalent circuit and a block circuit diagram of the entire device.

First, a base circuit substrate having a transistor was formed in the same manner as in Example 3. Then, a-Si _1-X G
e _X : H to a-Si _1-y C _y : H composition change layers 721, 722, 72
3 to form a multiplication region 713. Next, n-type a-Si
Example 6 A _1-X Ge _X : H layer (light shielding layer) 714 was formed and separated for each pixel, and a light absorption layer a-Si _1-X Ge _X : H layer 715 was formed.
Narrow gap p-type a-Si _1-X Ge _X : H
A layer 716 was formed, and a transparent electrode 717 for applying a bias voltage to the sensor was formed.

The collector electrode 718 is ohmically connected to the back surface of the substrate 701. Therefore, in the equivalent circuit of one pixel, as shown in FIG. 20, a p-channel MOS transistor 732, a capacitor 733, and a photoelectric conversion device 734 similar to the seventh embodiment are connected to the base of a bipolar transistor 731 made of crystalline silicon. A terminal 735 for applying a potential to the base;
A terminal 736 for driving the OS transistor 732 and the capacitor 733, a sensor electrode 737, an emitter electrode 738, and a collector electrode 739 are provided.

FIG. 21 is a circuit diagram in which one pixel cell 740 shown in FIGS. 19 and 20 is arranged in a 3 × 3 two-dimensional matrix.

Since the operation is the same as that of the third embodiment, the description of the operation is omitted.

As described above, according to the photoelectric conversion device of this embodiment, the light absorbing layer having a narrow band gap of Eg1 and absorbing light, and the light absorbing layer of Eg5 having a forbidden band width of n are used.
One or a plurality of layers each having a step-back structure in which a conduction band is continuously changed in a minimum band gap Eg2 and a maximum band gap Eg3 for multiplying carriers generated by absorbing light. And a multiplying layer formed between the light absorbing layer and the multiplying layer are reversed. Since it has a function as a bias layer, the carriers generated in the light absorbing layer are transported smoothly, and the forbidden band width Eg1 of the light absorbing layer is substantially equal to the forbidden band width Eg5 of the n-conductivity type layer. By doing so, the band mismatch between the light absorbing layer and the multiplication layer and various problems caused by the banding are solved, and the high-speed response caused by obstacles to the traveling property of carriers in the light absorbing layer due to the generation of interface states and the like. Can be prevented from lowering and the multiplication layer Have not simultaneously photodiode similar high-speed response is obtained, the band gap Eg of the light absorbing layer
By setting 1 to a forbidden band width particularly corresponding to infrared light, it was possible to impart high sensitivity to infrared light. Further, the light incidence on the multiplication layer was reduced, and the fluctuation of the multiplication factor due to the light incidence on the multiplication layer was reduced.

The light absorbing layer of the photoelectric conversion device of the present invention, n
Constituent elements such as the conductivity type layer, the multiplication layer, and the charge injection blocking layer are made of a non-single-crystal material containing at least Si atoms, so that the bandgap can be easily controlled and low-temperature lamination is possible. Various problems that occurred can be solved. Embodiment 10 Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1, 29, and 30.
Example 0 will be described. FIG. 1 is a schematic vertical sectional view showing a tenth embodiment of the photoelectric conversion device of the present invention.

The photoelectric conversion device shown in FIG.
1. A 500-nm thick n-type a-
The charge injection blocking layer 402 made of Si _1-x Ge _x : H, and the composition of a-Si _1-X Ge _X : H to a-Si _1-y C _y : H for carrier multiplication was changed. Multiplication region 403, n-type a-Si _1-x Ge _x : H layer (light-shielding layer) for preventing light from entering the multiplication region and increasing the internal electric field of the light absorption layer to improve carrier traveling. 404, a light absorption layer 405 made of a-Si _1-y C _y : H having a band gap wider than that of the light shielding layer 404 and having a thickness of about 1 μm for absorbing light and generating carriers, preventing electron injection. A charge injection blocking layer 406 made of p-type a-Si _1-y C _y : H and having a thickness of about 100 ° and a transparent electrode 407 mainly composed of indium oxide.

The Cr electrode 401 and the transparent electrode 407 are formed by EB evaporation, and the charge injection blocking layer 402, the multiplication region 403,
The amorphous layers of the n-type a-Si _1-x Ge _x : H layer 404, the light absorption layer 405, and the charge injection blocking layer 406 were formed by a plasma CVD method. The source gas for forming the amorphous layer is that the charge injection blocking layer 402 and the n-type a-Si _1-x Ge _x : H layer 404 are SiH ₄ , GeH ₄ , PH ₃ ,
H ₂ , the multiplication region 403 is SiH ₄ , GeH ₄ , CH ₄ , H ₂ , the light absorbing layer 40
5 is SiH ₄ , CH ₄ , H ₂ , and the charge injection blocking layer 406 is SiH ₄ , CH ₄ , B
₂ H ₆ and H ₂ were used.

The multiplication region 403 is composed of CH ₄ and Ge of the source gas.
Is made a gas flow rate of H ₄ of three layers of continuous composition change layer that changes are not forbidden band width of about 1.3eV to about 2.3eV thickness 200Å was continuously changed 411. The gas flow rate of PH ₄ when forming the n-type a-Si _1-x Ge _x : H layer 404 is slightly smaller than that of the charge injection blocking layer 402.

The energy band structure of the photoelectric conversion device of the tenth embodiment shown in FIG.
It is assumed that it is as shown in FIG.

FIG. 29 is an energy band diagram when the photoelectric conversion device of the tenth embodiment is in a non-biased state, and FIG. 30 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. is there.

FIGS. 29 and 34 show a-Si a-Si _1-x Ge _x : H layers 501 having a forbidden band width of Eg4 and a forbidden band width of about 1.3 eV.
_1-X Ge _{X: H~} forbidden band width of about _{2.4eV a-Si 1-y C} y: multiplication region 5 composed of three layers of H composition change layers 511, 512, and 513
02, the forbidden band width of the multiplication region 502 is Eg3, the forbidden band width of the n-type a-Si _1-x Ge _x : H layer 503 is Eg5, a-Si _1-y C _y : The forbidden band width of the H layer 504 is Eg1,
This shows that the forbidden band width of the p-type a-Si _1-y C _y : H layer 505 is Eg0.

In FIG. 29, there are energy discontinuities at both the conduction band edge and the valence band edge. However, when the bias voltage is applied, the direction in which the carrier travels can be seen from FIG. Has almost no barrier due to energy discontinuity and does not hinder the traveling properties of carriers.

The a-Si _1-y C _y : H layers 504, 5 prepared here
03 has a C composition ratio y of about 0.4 and a forbidden band width Eg1, Eg
g0 was about 2.3 eV. Composition change layers 511, 5
Layer maximum forbidden band width of 12,513 gives Eg3 also _{a-Si 1-y C y} : a H, Eg3 was about 2.3 eV.

The a-Si _1-x Ge _x : H layers 501 and 503
The Ge composition ratio x is about 0.6, and the forbidden band width Eg4 is about 1.3 eV
Met. The layer giving the minimum forbidden band width Eg2 among the composition change layers 511, 512, and 513 was also an a-Si _1-x Ge _x : H layer, and Eg2 was about 1.3 eV.

The light absorption coefficient of the light absorption layer 503 is
540nm to about 4 × 10 ³ to light in cm ^{- 1,} is about 3 × 10 ⁴ cm ^-1 or more for light having a wavelength of 350 nm, the absorption of the ultraviolet light is sufficiently performed.

The multiplication factor of this apparatus was about 10 times or more when a bias of 10 V was applied. Also, for ultraviolet light having a wavelength of 400 nm or less, there was no change in the multiplication factor even when the wavelength was changed. Furthermore, the leakage current in the dark was as low as about 1 nA / cm ² or less when a bias of 10 V was applied. Furthermore, the optical response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 502, and was high. Embodiment 11 Hereinafter, an eleventh embodiment of the present invention will be described with reference to FIGS. 31 and 32 show an eleventh embodiment of the present invention.
It is an energy band structure figure assumed ideally of an Example.

FIG. 31 is an energy band diagram when the photoelectric conversion device of the eleventh embodiment is in a non-biased state, and FIG. 32 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. It is.

The photoelectric conversion device shown in FIG. 31 has a wide gap n-type a-Si ₁ -yC _y : H layer 60 having a forbidden band width Eg 4 ′.
2 except that it has an N-type a-Si _1-y C _y : H layer 603 having a forbidden band width Eg5 ′ and a wide gap.
Is the same as _{9, a-Si 1-X} Ge X: H~a-Si 1-y C y: multiplication region 60 consisting of three layers of H composition change layers 611, 612, 613
The minimum forbidden bandwidth of Eg2 is 2, the maximum forbidden bandwidth is Eg3, and a-
Si _1-y C _y : The forbidden band width of the H layer 604 is Eg1, and the p-type a-Si _1-y C
_y : indicates that the forbidden band width of the H layer 605 is Eg0.

The multiplication factor of this device was about 10 times or more when a bias of 10 V was applied. Further, even when the wavelength was changed for ultraviolet light having a wavelength of 400 nm or less, the gain did not change. Furthermore, the leakage current in the dark was as low as about 0.1 nA / cm ² or less when a bias of 10 V was applied. Furthermore, the light response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 602, and was high. (Embodiment 12) In this embodiment, the light absorption layer of the photoelectric conversion device shown in Embodiment 6 is stacked on a scanning circuit and a readout circuit in the same manner as in Embodiment 6, except that the forbidden band width is made larger than the light shielding layer. This is a working example.

FIG. 19 is a schematic sectional view of the vicinity of the light receiving section according to the embodiment of the present invention, FIG. 20 is an equivalent circuit diagram of one pixel, and FIG. 21 is an equivalent circuit and a block circuit diagram of the entire device.

A base circuit substrate having a transistor was formed in the same manner as in Example 3.

[0235] _{Then, a-Si 1-X Ge} X: H~a-Si 1-y C y: multiplication region 7 to form a composition change layer 721 in H
13. Next, an n-type a-Si _1-x Ge _x : H layer 714 is formed and separated for each pixel, and a light absorption layer a-Si _1-y C _y : H layer 715 is formed.
Was formed, a p-type a-Si _1-y C _y : H layer 716 was formed, and a transparent electrode 717 for applying a bias voltage to the sensor was formed.

The collector electrode 718 is ohmically connected to the back surface of the substrate 701. Therefore, in the equivalent circuit of one pixel, as shown in FIG. 20, a p-channel MOS transistor 732, a capacitor 733, and a photoelectric conversion device 734 similar to the tenth embodiment are connected to the base of a bipolar transistor 731 made of crystalline silicon. A terminal 735 for applying a potential to the base, a terminal 736 for driving the p-channel MOS transistor 732 and the capacitor 733, a sensor electrode 737, an emitter electrode 738, and a collector electrode 739 are represented.

FIG. 21 shows a circuit configuration in which one pixel cell 740 shown in FIGS. 19 and 20 is arranged in a 3 × 3 two-dimensional matrix.

Since the operation is the same as that of the third embodiment, the description of the operation is omitted.

According to the photoelectric conversion device of this embodiment, Eg1
A light absorbing layer having a forbidden band width to absorb light, an n-conductivity type layer (light shielding layer) having a forbidden band width of Eg5, and a minimum forbidden band width Eg2 for multiplying carriers generated by absorbing light. A layer in which one layer having a step-back structure in which the forbidden band width of the maximum forbidden band width Eg3 is continuously changed or a multiplication layer formed by laminating a plurality of layers is sequentially sandwiched between the charge injection blocking layers. By doing so, the n-conductivity type layer located between the light absorbing layer and the multiplication layer functions as a reverse bias layer, so that carriers generated in the light absorbing layer are smoothly transported, and By making the forbidden band width Eg1 of the absorbing layer larger than the forbidden band width Eg5 of the n-conductivity type layer, the light absorbing layer,
The band mismatch of the multiplication layer and various problems caused by the mismatch are solved, and a decrease in the high-speed response caused by an obstacle to the traveling property of the carrier in the light absorption layer due to the generation of an interface state can be prevented. In addition, a high-speed response similar to that of a photodiode having no multiplication layer can be obtained, and at the same time, the forbidden band width Eg1 of the light absorbing layer is set to a forbidden band width particularly corresponding to ultraviolet light, thereby achieving high sensitivity to ultraviolet light. Can be provided.

When the forbidden band width Eg5 of the n-conductivity type layer is a narrow forbidden band width, the incidence of light on the multiplication layer is reduced, so that the fluctuation of the multiplication factor can be reduced.

Further, by selecting the number of layers of the step-back structure, a multiplication factor of 2 or more was obtained and low noise was obtained.

Further, the light absorption layer of the photoelectric conversion device of the present invention,
The non-monocrystalline material containing at least Si atoms constitutes the n-conductivity-type layer, the multiplication layer, the charge injection blocking layer, and other components, enabling easy control of the forbidden band width and low-temperature lamination. The various problems caused by the above can be solved. Embodiment 13 Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1, 33, and 34.
Three embodiments will be described.

FIG. 1 is a schematic longitudinal sectional structural view showing a photoelectric conversion device according to a thirteenth embodiment of the present invention. The photoelectric conversion device shown in FIG. 1 includes a Cr electrode 401, a charge injection blocking layer 402 made of n-type a-Si _1-x Ge _x : H having a thickness of about 500 ° for blocking hole injection, and carrier multiplication. To do a-Si _1-x G
e _x : H to a-Si _1-y C _y : Multiplication region 40 in which the composition of H is changed
3. n-type a-Si for preventing light from entering the multiplication region and for enhancing the internal electric field of the light absorption layer to improve the traveling of carriers.
_1-x Ge _x: H layer (light-shielding layer) 404, a thickness of about 2μm for generating absorb light and carriers _{a-Si: H~a-Si 1} -y C y: changing the composition of H Light absorption layer 405, charge injection blocking layer 406 made of p-type a-Si: H having a thickness of about 100 ° for blocking electron injection, and transparent electrode 40 mainly composed of indium oxide.
7 are provided.

The Cr electrode 401 and the transparent electrode 407 are formed by EB evaporation, and the charge injection blocking layer 402, the multiplication region 403,
The amorphous layers of the n-type a-Si _1-x Ge _x : H layer 404, the light absorption layer 405, and the charge injection blocking layer 406 were formed by a plasma CVD method. The source gas for forming the amorphous layer is that the charge injection blocking layer 402 and the n-type a-Si _1-x Ge _x : H layer 404 are SiH ₄ , GeH ₄ , PH ₃ ,
H ₂ , the multiplication region 403 is SiH ₄ , GeH ₄ , CH ₄ , H ₂ , the light absorbing layer 40
5 is SiH ₄ , CH ₄ , H ₂ , the charge injection blocking layer 406 is SiH ₄ , B ₂ H ₆ ,
The H ₂ was used.

The multiplication region 403 includes CH ₄ and Ge of the source gas.
It is composed of three layers of composition change layers 411, 412, and 413 each having a thickness of 200 ° and a H ₄ gas flow rate continuously changed. The gas flow rate of PH _{3 in} the n-type a-Si _1-x Ge _x : H layer 404 is slightly smaller than that in the charge injection blocking layer 402. The light absorption layer 405 is formed by continuously changing the gas flow rate of CH ₄ among the source gases.

The energy band structure of the photoelectric conversion device of the thirteenth embodiment shown in FIG. 1 is ideally shown in FIGS.
It is assumed that it is as shown in FIG.

FIG. 33 is an energy band diagram when the photoelectric conversion device of the thirteenth embodiment is in a non-biased state, and FIG. 34 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. is there.

FIGS. 33 and 34 show that the forbidden band width of the n-type a-Si _1-x Ge _x : H layer 501 is Eg4 and a-Si _{1- x} Ge _x : H to a-Si _1-y C _y :
H The minimum forbidden band width of the multiplication region 502 composed of three layers of the composition change layers 511, 512, and 513 is Eg2, and the multiplication region 5
02 has a maximum forbidden band width of Eg3 and an n-type a-Si _1-x Ge _x : H layer 50
Bandgap of 3 Eg5, a-Si: H~a- Si 1-y C y: minimum forbidden band width of the H composition change layer 504 Eg1, p-type a-Si: H layer 505
Indicates that the forbidden band width is Eg0.

In FIG. 33, there are energy discontinuities at both the conduction band edge and the valence band edge. However, in the state where the bias voltage is applied, the direction in which the carrier travels can be seen from FIG. Has almost no barrier due to energy discontinuity and does not hinder the traveling properties of carriers.

The composition change layers 511, 51 prepared here
The layer giving the maximum bandgap Eg3 of 2,513 is C
A-Si _1-y C _y : H with a composition ratio y of about 0.4, and Eg3 of about 2.
3 eV. a-Si: H to a-Si _1-y C _y : H composition change layer 504
The layer giving the maximum forbidden band width was also a-Si _1-y C _y : H.

The a-Si _1-x Ge _x : H layers 501 and 503
The Ge composition ratio x is about 0.6, and the forbidden band width Eg4 is about 1.3 eV
Met. The layer giving the minimum forbidden band width Eg2 among the composition change layers 511, 512, and 513 was also an a-Si _1-x Ge _x : H layer, and Eg2 was about 1.3 eV. a-Si: H〜a-Si _1-y C _y : H
The layer giving the minimum forbidden band width Eg1 of the composition change layer 504 is a-
Si: H and Eg1 was about 1.8 eV. The forbidden band width Eg0 of the p-type a-Si: H layer 505 was also about 1.8 eV.

The light absorption coefficient of the light absorption layer 504 is the wavelength
Against 700 nm light about 6 × 10 ³ cm ^{- 1,} is about 3 × 10 ⁴ cm ^-1 or more for the wavelength 350 nm of the light absorption of the ultraviolet light from the visible portion of light is sufficiently performed I have.

The multiplication factor of this device was about 10 times or more when a bias of 10 V was applied. In addition, there was no change in the multiplication factor even when the wavelength was changed for visible to ultraviolet light having a wavelength of 700 nm or less. Furthermore, the leakage current in the dark was as low as about 1 nA / cm ² or less when a bias of 10 V was applied. Furthermore, the optical response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 502, and was high. Embodiment 14 Hereinafter, a fourteenth embodiment of the present invention will be described with reference to FIGS.

FIG. 35 and FIG. 36 are energy band structure diagrams assumed ideally in the fourteenth embodiment of the present invention.

FIG. 35 is an energy band diagram when the photoelectric conversion device of the fourteenth embodiment is in a non-biased state, and FIG. 36 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. is there.

The photoelectric conversion device shown in the energy band diagram shown in FIG. 35 has an n-type a-Si ₁ -yC _y : H layer 601 having a forbidden band width Eg 4 ′.
33, that the region of the a-Si: H composition of the light absorbing layer 604 is wider than that of FIG. 33, and that the n-type a-Si having the forbidden band width Eg5 ′.
Except for being a _1-y C _y : H layer (light-shielding layer) 603, it is the same as the photoelectric conversion device of Example 13, and a-Si _1-x Ge _x : H to a-Si
_1-y C _y : H The minimum bandgap of the multiplication region 602 composed of three layers of the composition change layers 611, 612, and 613 is Eg2, the maximum bandgap is Eg3, and a-Si: H to a-Si _{1- y} C _y : The minimum band gap of the H layer 604 is Eg1, and the band gap of the p-type a-Si: H layer 605 is Eg.
0 is shown.

The multiplication factor of this device was about 10 times or more when a bias of 10 V was applied. Further, even if the wavelength was changed for light having a wavelength of 700 nm or less, there was no change in the multiplication factor.
Furthermore, the leakage current in the dark was as low as about 1 nA / cm ² or less when a bias of 10 V was applied. Furthermore, the light response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 602, and was high. (Embodiment 15) This embodiment is an embodiment in which the photoelectric conversion device shown in Embodiment 13 is stacked on the scanning circuit and the readout circuit shown in Embodiment 3.

FIG. 19 is a schematic sectional view of the vicinity of the light receiving section according to the embodiment of the present invention, FIG. 20 is an equivalent circuit diagram of one pixel, and FIG. 21 is an equivalent circuit and block circuit diagram of the entire device.

In the same manner as in Example 3, a base circuit substrate having a transistor was formed.

Subsequently, the composition change layers 721, 722, and 723 of a-Si _1-x Ge _x : H to a-Si _1-y C _y : H are formed to form the multiplication region 7
13 were constructed. Next, an n-type a-Si _1-x Ge _x : H layer 714 is formed and separated for each pixel, and the light absorption layers a-Si: H to a-Si _1-y C _y : H
A composition change layer 715 is formed, a p-type a-Si: H layer 716 is formed, and a transparent electrode 7 for applying a bias voltage to the sensor is formed.
17 was formed.

The collector electrode 718 is ohmically connected to the back surface of the substrate 701. Therefore, as shown in FIG. 20, in the equivalent circuit of one pixel, a p-channel MOS transistor 732, a capacitor 733, and a photoelectric conversion device 734 similar to the thirteenth embodiment are connected to the base of a bipolar transistor 731 made of crystalline silicon. A terminal 735 for applying a potential to the base, a terminal 736 for driving the p-channel MOS transistor 732 and the capacitor 733, a sensor electrode 737, an emitter electrode 738, and a collector electrode 739 are represented.

FIG. 21 is a circuit diagram in which one pixel cell 740 shown in FIGS. 19 and 20 is arranged in a 3 × 3 two-dimensional matrix.

Since the operation is the same as that of the third embodiment, the description of the operation is omitted.

According to the photoelectric conversion device of this embodiment, Eg1
A light absorbing layer having a forbidden band width and absorbing light; an n-conductivity type layer having a forbidden band width of Eg5; a minimum forbidden band width Eg2 for multiplying carriers generated by absorbing light; Eg3
A layer having a step-back structure in which the forbidden band width changes continuously or a multiplying layer formed by laminating a plurality of layers is sandwiched between the charge injection blocking layers. Since the n-conductivity type layer interposed between the light absorbing layer and the multiplication layer has a function as a reverse bias layer, carriers generated in the light absorbing layer are smoothly transported, and furthermore, the forbidden band of the light absorbing layer. The width Eg1 changes so as to be continuously larger than one of the stacked charge injection blocking layers on the light absorbing layer, and the forbidden band width Eg of the light absorbing layer adjacent to the n-conductivity type layer is changed.
By setting 1 to be equal to or larger than the forbidden band width Eg5 of the n-conductivity type layer, band mismatch between the light absorption layer and the multiplication layer and various problems caused by the band gap can be solved, and light due to generation of interface states can be solved. In the absorption layer, it is possible to prevent a decrease in high-speed responsiveness caused by obstacles to the traveling property of carriers, and to obtain high-speed responsiveness similar to a photodiode having no multiplication layer, and at the same time, to forbid the band gap of the light absorption layer. By setting the width Eg1 to be a forbidden band width particularly corresponding to visible light to ultraviolet light, high sensitivity can be provided from visible light to ultraviolet light.

When the forbidden band width Eg5 of the n-conductivity type layer is a narrow forbidden band width, the incidence of light on the multiplication layer is reduced, so that the fluctuation of the multiplication factor due to the light incidence on the multiplication layer is reduced. be able to.

Also, by selecting the number of layers of the step-back structure, a multiplication factor of 2 or more was obtained and low noise was obtained.

Further, the light absorbing layer of the photoelectric conversion device of the present invention,
The non-monocrystalline material containing at least Si atoms constitutes the n-conductivity-type layer, the multiplication layer, the charge injection blocking layer, and other components, enabling easy control of the forbidden band width and low-temperature lamination. The various problems caused by the above can be solved. Embodiment 16 Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1, 37, and 38.
Six embodiments will be described.

FIG. 1 is a schematic vertical sectional view showing a sixteenth embodiment of the photoelectric conversion device of the present invention. The photoelectric conversion device shown in FIG. 1 includes a Cr electrode 401, a charge injection blocking layer 402 made of n-type a-Si _1-x Ge _x : H having a thickness of about 500 ° for blocking hole injection, and carrier multiplication. To do a-Si _1-x G
e _x : H to a-Si _1-y C _y : Multiplication region 40 in which the composition of H is changed
3. n-type a-Si for preventing light from entering the multiplication region and for enhancing the internal electric field of the light absorption layer to improve the traveling of carriers.
_1-x Ge _x : H layer (light-shielding layer) 404, which changes the composition of a-Si: H to a-Si _1-x Ge _x : H having a thickness of about 1 μm for absorbing light and generating carriers. Light absorption layer 405, charge injection blocking layer 406 made of p-type a-Si: H having a thickness of about 100 ° for blocking electron injection, and transparent electrode 40 mainly composed of indium oxide.
7 are provided.

The Cr electrode 401 and the transparent electrode 407 are formed by EB evaporation, and the charge injection blocking layer 402, the multiplication region 403,
The amorphous layers of the n-type a-Si _1-x Ge _x : H layer 404, the light absorption layer 405, and the charge injection blocking layer 406 were formed by a plasma CVD method. The source gas for forming the amorphous layer is SiH ₄ , GeH ₄ , PH for the charge injection blocking layer 402 and the n-type a-Si _1-x Ge _x : H layer 404.
_{3, H 2, SiH 4,} GeH 4, CH 4, H 2 in the multiplication region _{403, SiH 4, GeH 4,} H 2 for the light-absorbing layer 405, the charge injection blocking layer 406
SiH ₄ , B ₂ H ₆ and H ₂ were used.

The multiplication region 403 is composed of CH ₄ and Ge of the source gas.
It is composed of three layers of composition change layers 411, 412, and 413 each having a thickness of 200 ° and a H ₄ gas flow rate continuously changed. The gas flow rate of PH _{3 in} the n-type a-Si _1-x Ge _x : H layer 404 is slightly smaller than that in the charge injection blocking layer 402. The light absorbing layer 405 is formed by continuously changing the gas flow rate of GeH ₄ among the source gases.

The energy band structure of the photoelectric conversion device of the sixteenth embodiment shown in FIG. 1 is ideally shown in FIGS.
It is assumed that it is as shown in FIG.

FIG. 37 is an energy band diagram when the photoelectric conversion device of the sixteenth embodiment is in a non-biased state, and FIG. 38 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. is there.

FIGS. 37 and 38 show that the forbidden band width of the n-type a-Si _1-x Ge _x : H layer 501 is Eg4 and a-Si _{1- x} Ge _x : H to a-Si _1-y C _y :
H The minimum forbidden band width of the multiplication region 502 composed of three layers of the composition change layers 511, 512, and 513 is Eg2, and the multiplication region 5
02 has a maximum forbidden band width of Eg3 and an n-type a-Si _1-x Ge _x : H layer 50
Bandgap of 3 Eg5, a-Si: H~a- Si 1-x Ge x: H layer 504
Indicates that the maximum forbidden band width is Eg1, and the forbidden band width of the p-type a-Si: H layer 505 is Eg0.

In FIG. 37, there are energy discontinuities at both the conduction band edge and the valence band edge. In the state where the bias voltage is applied, as shown in FIG. Has almost no barrier due to energy discontinuity and does not hinder the traveling properties of carriers.

The composition change layers 511, 51 prepared here
The layer giving the maximum bandgap Eg3 of 2,513 is C
A-Si _1-y C _y : H with a composition ratio y of about 0.4, and Eg3 of about 2.
3 eV.

The a-Si _1-x Ge _x : H layers 501 and 503
The Ge composition ratio x is about 0.6, and the forbidden band width Eg4 is about 1.3 eV
Met. The layer giving the minimum forbidden band width Eg2 among the composition change layers 511, 512, and 513 was also an a-Si _1-x Ge _x : H layer, and Eg2 was about 1.3 eV. a-Si: H〜a-Si _1-x Ge _x : H
The layer giving the maximum bandgap Eg1 of the layer 504 was a-Si: H, and Eg1 was about 1.8 eV. The forbidden band width Eg0 of the p-type a-Si: H layer 505 was also about 1.8 eV.

The light absorption coefficient of the light absorption layer 504 is the wavelength
About 1 × 10 relative to 400 nm of the light ⁵ cm ^{- 1} or more, wavelength 1000nm
About 2 × 10 ⁴ cm ⁻¹ or more with respect to infrared light,
Light was sufficiently absorbed over visible light and ultraviolet light.

The multiplication factor of this device was about 10 times or more when a bias of 10 V was applied. Also, for light having a wavelength of 1000 nm or less, there was no change in the gain even when the wavelength was changed. Furthermore, the leakage current in darkness is about 1 when a bias of 10 V is applied.
It was as low as nA / cm ² or less. Furthermore, the optical response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 502, and was high. Embodiment 17 Hereinafter, a seventeenth embodiment of the present invention will be described with reference to FIGS.

FIGS. 39 and 40 are ideally assumed energy band structures of the seventeenth embodiment of the present invention.

FIG. 39 is an energy band diagram when the photoelectric conversion device of the seventeenth embodiment is in an unbiased state, and FIG. 40 is an energy band diagram when a bias is applied to perform a carrier multiplying operation. is there.

The photoelectric conversion device shown in FIG.
wide-gap n-type a-Si _{1- y} C _y of g4 ': and it is H layer 601, the light absorbing layer 604 a-Si: area of H composition 37
37 except that it is wider than the photoelectric conversion device of FIG. The forbidden band width of each layer is a-Si _1-x Ge _x : H to a-Si _1-y C _y : H
The multiplication region 602 composed of three layers of the composition change layers 611, 612, and 613 has a minimum forbidden band width of Eg2 and a maximum forbidden band width of E.
g3, the forbidden band width of the n-type a-Si _1-x Ge _x : H layer 603 is Eg5,
_{a-Si: H~a-Si 1} -x Ge x: maximum forbidden band width of the H layer 604 is Eg
1, indicating that the forbidden band width of the p-type a-Si: H layer 605 is Eg0.

The multiplication factor of this apparatus was about 10 times or more when a bias of 10 V was applied. Further, even if the wavelength was changed for light having a wavelength of 1000 nm or less, there was no change in the multiplication factor. Furthermore, the leakage current in darkness is about 1 when a bias of 10 V is applied.
It was as low as nA / cm ² or less. Furthermore, the light response speed was equivalent to that of the pin-type photoelectric conversion device without the multiplication layer 602, and was high. (Embodiment 18) This embodiment is an embodiment in which the photoelectric conversion device shown in Embodiment 16 is stacked on the scanning circuit and the readout circuit shown in Embodiment 3.

FIG. 19 is a schematic sectional view of the vicinity of the light receiving section according to the embodiment of the present invention, FIG. 20 is an equivalent circuit diagram of one pixel, and FIG. 21 is an equivalent circuit and block circuit diagram of the entire device.

First, a base circuit substrate having a transistor was formed in the same manner as in Example 3. Then, a-Si _1-X G
e _X : H to a-Si _1-y C _y : H composition change layers 721, 722, 72
3 to form a multiplication region 713. Next, n-type a-Si
_{A 1-X} Ge _X : H layer 714 is formed and separated for each pixel, and a light absorption layer a-Si: H to a-Si _1-X Ge _X : H composition change layer 715 is formed.
A mold a-Si: H layer 716 was formed, and a transparent electrode 717 for applying a bias voltage to the sensor was formed.

A collector electrode 718 is ohmically connected to the back surface of the substrate 701. Therefore, in the equivalent circuit of one pixel, as shown in FIG. 20, a p-channel MOS transistor 732, a capacitor 733, and a photoelectric conversion device 734 similar to the first embodiment are connected to the base of a bipolar transistor 731 made of crystalline silicon. A terminal 735 for applying a potential to the base;
A terminal 736 for driving the OS transistor 732 and the capacitor 733, a sensor electrode 737, an emitter electrode 738, and a collector electrode 739 are provided.

FIG. 21 shows a circuit configuration in which one pixel cell 740 shown in FIGS. 19 and 20 is arranged in a 3 × 3 two-dimensional matrix.

Since the operation is the same as that of the third embodiment, the description of the operation is omitted.

According to the photoelectric conversion device of this embodiment, Eg1
A light absorbing layer having a forbidden band width and absorbing light; an n-conductivity type layer having a forbidden band width of Eg5; a minimum forbidden band width Eg2 for multiplying carriers generated by absorbing light; Eg3
A layer having a step-back structure in which the forbidden band width changes continuously or a multiplying layer formed by laminating a plurality of layers is sandwiched between the charge injection blocking layers. The n-conductivity type layer (light-shielding layer) between the light absorbing layer and the multiplication layer functions as a reverse bias layer, and the band gap of the light absorbing layer changes in the carrier transport direction. Therefore, the carriers generated in the light absorption layer are smoothly transported to the multiplication layer, and the forbidden band width Eg1 of the light absorption layer is continuously reduced from one of the charge injection blocking layers stacked on the light absorption layer. And the forbidden band width Eg1 of the light absorption layer adjacent to the n-conductivity type layer (light shielding layer) is substantially equal to the forbidden band width Eg5 of the n-conductivity type layer. The band mismatch of the light absorption layer and the multiplication layer and the various problems caused by them are solved. As a result, it is possible to prevent a decrease in the high-speed responsiveness caused by obstacles to the traveling properties of carriers in the light absorbing layer due to the generation of interface states, etc., and obtain the same high-speed responsiveness as a photodiode having no multiplication layer. At the same time, by setting the forbidden band width Eg1 of the light-absorbing layer to a forbidden band width particularly corresponding to infrared light to ultraviolet light, high sensitivity was obtained from infrared light to ultraviolet light.

Further, since the n-conductivity type layer (light-shielding layer) is provided between the light absorbing layer and the multiplication layer, the incidence of light on the multiplication layer is reduced, so that the fluctuation of the multiplication factor can be reduced. Was.

The light absorbing layer of the photoelectric conversion device of the present invention,
The non-single-crystalline material containing at least Si atoms constitutes the n-conductivity type layer, the multiplication layer, the charge injection blocking layer, and other components, enabling easy control of the forbidden band width and low-temperature lamination. The various problems caused by the above can be solved. (Example 19) A photoelectric conversion device in which a light shielding layer was formed of graphite was formed.

As shown in the schematic vertical sectional view of FIG. 1, the photoelectric conversion device of this embodiment has a Cr—Ag alloy electrode 4
01, a thickness of about 50 to prevent hole injection from the electrode
0 ° n-type a-Si _0.55 Ge _0.45 : H charge injection blocking layer 402 made of a-Si for carrier multiplication
_{1-x Ge x: H~a-} Si 1-y C y: multiplication region 403 and the composition of the H is changed, the light-shielding layer 404 where light in the bulking multiplication region consists of graphite prevented from entering the light A-Si: H light absorbing layer 40 for absorbing and generating carriers
5, a charge injection blocking layer 406 made of P-type a-Si: H having a thickness of about 100 ° and a transparent electrode 407 made of indium oxide and tin oxide.

A Cr—Ag alloy electrode 401 having a thickness of about 1.1 μm was formed on a quartz glass base material by a normal EB evaporation method.
m, and a charge injection blocking layer 402 having a thickness of about 500 ° was formed thereon by a normal plasma CVD method using SiH ₄ , GeH ₄ , PH ₃ , and H ₂ as source gases.

Subsequently, the multiplication region 403 is formed by plasma CVD.
Source gas (SiH ₄ , CH ₄ , GeH ₄ , H
_{In a} ), a-Si _1-y C _y : H having a maximum forbidden band width of 2.8 eV by continuously changing the gas flow rates of CH ₄ and GeH _4.
And the composition change layers 411, 412, and 413 made of a-Si _1-x Ge _x : H having a minimum forbidden band width of 1.4 eV and three layers each having a thickness of 190 °.

A light-shielding layer 404 made of polycrystalline graphite having a thickness of about 3500 ° was formed on the multiplication region 403 thus formed by sputtering. Subsequently, the light-absorbing layer 405 having a thickness of about 1 μm was formed on the light-shielding layer by plasma CVD using SiH ₄ and H ₂ as source gases, and SiH ₄ , B ₂ H ₆ and H ₂ were used as source gases. Thus, a charge injection blocking layer 406 having a thickness of about 100 ° was formed.
In ₂ O _{3 is} deposited on the charge injection blocking layer 406 by EB evaporation.
And a transparent electrode 407 containing SnO ₂ .

The photoelectric conversion device of this embodiment thus formed has a multiplication factor of about 11 when a bias of 12 V is applied,
The sensitivity was high without any change in the multiplication factor over the entire visible light range. The leakage current in the dark was as low as about 1.1 nA / cm ² or less when a bias of 12 V was applied.

Further, the photoresponse speed is p
It was equivalent to an in-type photoelectric conversion device and operated at high speed.

[0297]

As described above in detail, according to the photoelectric conversion device of the present invention, the light absorption layer independent of the multiplication layer is provided on the multiplication layer via the light shielding layer. Variations in the multiplication factor due to intrusion of incident light into the multiplication layer, which has caused the characteristics of the conventional photoelectric conversion device to be unstable, can be reduced.

According to the photoelectric conversion device of the present invention, the multiplication layer has a maximum forbidden band width Eg3 and a minimum forbidden band width Eg2.
ΔEc, which is a difference in conduction band energy, is multiplied by electrons in the step-back structure layer, and low noise and a sufficient multiplication factor can be obtained.

Also, according to the photoelectric conversion device of the present invention, a film forming method capable of forming a film at a relatively low temperature, for example, a plasma CVD method
It can be easily formed on a large-area substrate at a low temperature (for example, 200 to 300 ° C.) by a method or the like, and the forbidden band width can be easily controlled and the composition can be modulated. In addition to the above, the thermal diffusion of atoms due to heat etc. is suppressed, and a relatively reliable step-back structure
For example, it is possible to reduce problems in laminating the layers.

According to the photoelectric conversion device of the present invention, each layer is formed because it has a light absorption layer that absorbs light to generate photocarriers and a multiplication layer that multiplies the carriers. The degree of freedom in material selection can be increased.

Further, according to the photoelectric conversion device of the present invention, sensitivity to incident light having a desired wavelength is increased, noise is reduced, and
A large area can be easily achieved, and a reduction in thickness can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a photoelectric conversion device of the present invention.

FIG. 2 is a structural diagram of an energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 3 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 4 is a structural diagram of an energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 5 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 6 is a diagram for explaining an energy state of a multiplication layer.

FIG. 7 is a diagram for explaining an energy state of a multiplication layer.

FIG. 8 is a diagram for explaining an energy state of a multiplication layer.

FIG. 9 is a diagram for explaining an energy state of a multiplication layer in which a hetero semiconductor is joined.

FIG. 10 is a diagram for explaining an electric field intensity distribution in a case where an impurity is contained in the junction of the multiplication layer and in the vicinity thereof.

FIG. 11 is a structural diagram of an energy band of a multiplication layer containing impurities when no bias is applied.

FIG. 12 is a diagram for explaining an energy state of a multiplication layer.

FIG. 13 is a diagram for explaining an energy state of a multiplication layer.

FIG. 14 is a diagram for explaining an energy state of a multiplication layer.

FIG. 15 is a structural diagram of an energy band at the time of no bias in an embodiment of the multiplication layer.

FIG. 16 is a structural diagram of an energy band when a bias is applied in one embodiment of the multiplication layer.

FIG. 17 is a structural diagram of an energy band of the photoelectric conversion device of the present invention when no bias is applied.

FIG. 18 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 19 is a schematic longitudinal sectional view of a photoelectric conversion device having a multiplication layer, a light shielding layer, and a light absorption layer on a base circuit substrate.

20 is an equivalent circuit diagram of the photoelectric conversion device shown in FIG.

21 is a diagram for describing a photoelectric conversion device in which the photoelectric conversion devices illustrated in FIG. 20 are arranged in a matrix in one pixel.

FIG. 22 is a block diagram illustrating a configuration of a photoelectric conversion device.

FIG. 23 is a structural diagram of the energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 24 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 25 is a structural diagram of an energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 26 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 27 is a structural diagram of the energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 28 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 29 is a structural diagram of an energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 30 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 31 is a structural diagram of an energy band of the photoelectric conversion device of the present invention when no bias is applied.

FIG. 32 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 33 is a structural diagram of the energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 34 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 35 is a structural diagram of an energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 36 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 37 is a structural diagram of the energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 38 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 39 is a structural diagram of an energy band of the photoelectric conversion device of the present invention when there is no bias.

FIG. 40 is a structural diagram of an energy band when a bias is applied to the photoelectric conversion device of the present invention.

FIG. 41 is a schematic cross-sectional view showing the structure of a conventional avalanche photodiode for optical communication (APD).

FIG. 42 is a schematic cross-sectional view showing the structure of a conventional APD having a step-back structure.

FIG. 43 is a structural diagram of an energy band of a bandgap gradient layer of a conventional APD when no bias is applied.

FIG. 44 is a structural diagram of an energy band of a band gap gradient layer when a reverse bias is applied to a conventional APD.

[Explanation of symbols]

401 electrode, 402 n-type semiconductor layer, 403 multiplication layer, 404 light shielding layer, 405 light absorption layer, 406 p
Type semiconductor layer, 407 electrode, 411 step back structure layer, 412 step back structure layer, 413
Step back structure layer.

──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 2-49599 (32) Priority date Hei 2 (1990) March 2 (33) Priority claim country Japan (JP) (31) Priority Claim number Japanese Patent Application No. 2-49600 (32) Priority Date Hei 2 (1990) March 2 (33) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application No. 2-49601 (32) Priority Japan 2 (1990) March 2 (33) Priority country Japan (JP) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31/10-31/107

Claims (31)

(57) [Claims] 1. A photoelectric conversion device having a light absorption layer that generates carriers by absorbing incident light and a multiplication layer that multiplies the carriers, wherein a photoelectric conversion device is provided between the light absorption layer and the multiplication layer. Transmit through the light absorbing layer
A light- shielding layer for preventing the reflected light from being incident on the multiplication layer.
And unnecessary carriers from the outside are
And charge injection blocking for preventing injection into the multiplication layer.
A photoelectric conversion device comprising a stop layer . 2. The multiplying layer is formed by laminating one or more layers having a step-back structure in which a forbidden band width of a minimum forbidden band width Eg2 and a maximum forbidden band width Eg3 are continuously changed. 2. The photoelectric conversion device according to 1. 3. The photoelectric conversion device according to claim 1, wherein the multiplication layer is formed by alternately stacking layers having a high dielectric constant and layers having a low dielectric constant. 4. The photoelectric conversion device according to claim 1, wherein the light absorption layer is made of a non-single-crystal material. 5. The photoelectric conversion device according to claim 1, wherein the multiplication layer is made of a non-single-crystal material. 6. The charge injection blocking layer has a thickness of 50 ° or less.
Above, not more than 2000 ° and conductivity of not more than 10 ^-4 S / cm
6. The process according to claim 1, wherein the upper layer is a p-type or n-type layer.
The photoelectric conversion device according to claim 1. 7. The light-shielding layer is made of a metal material.
The photoelectric conversion device according to claim 6. 8. The photoelectric conversion device according to claim 1, wherein the light-shielding layer is a semiconductor material containing a high concentration of impurities. 9. The photoelectric conversion device according to claim 1, wherein the light shielding layer is made of a conductive ceramic material. 10. The photoelectric conversion device according to claim 1, wherein a forbidden band width Eg1 of the light absorbing layer is substantially uniform in a layer thickness direction. 11. The photoelectric conversion device according to claim 1, wherein a forbidden band width Eg1 of the light absorbing layer is non-uniform in a layer thickness direction. 12. A photoelectric conversion device having a light absorption layer that generates carriers by absorbing incident light and a multiplication layer that multiplies the carriers, wherein a first electrode and a first electrode are connected to each other. A first charge injection blocking layer for preventing necessary carriers from being injected into the photoelectric conversion device, the multiplication layer, and light entering the multiplication layer to prevent a change in multiplication factor from occurring. A light-blocking layer for preventing light, the light-absorbing layer, a second charge injection-blocking layer for preventing unnecessary carriers from being injected from the second electrode into the photoelectric conversion device, and a light-transmitting layer. A photoelectric conversion device comprising a second electrode and a second electrode in this order. 13. The multiplying layer has a minimum forbidden band width Eg2,
13. The photoelectric conversion device according to claim 12, wherein one or more layers having a step-back structure in which a forbidden band width of a maximum forbidden band width Eg3 continuously changes are stacked. 14. The photoelectric conversion device according to claim 12, wherein the multiplication layer is formed by alternately stacking layers having a high dielectric constant and layers having a low dielectric constant. 15. The photoelectric conversion device according to claim 12, wherein the light absorption layer is made of a non-single-crystal material. 16. The photoelectric conversion device according to claim 12, wherein the multiplication layer is made of a non-single-crystal material. 17. The light shielding layer is made of a metal material.
The photoelectric conversion device according to claim 2. 18. The photoelectric conversion device according to claim 12, wherein said light-shielding layer is a semiconductor material containing impurities at a high concentration. 19. The photoelectric conversion device according to claim 12, wherein the light shielding layer is made of a conductive ceramic material. 20. The photoelectric conversion device according to claim 12, wherein a forbidden band width Eg1 of the light absorption layer is substantially uniform in a layer thickness direction. 21. The photoelectric conversion device according to claim 12, wherein a forbidden band width Eg1 of the light absorption layer is non-uniform in a layer thickness direction. 22. A photoelectric conversion device for outputting electric signals generated by a plurality of photoelectric conversion units, comprising: a light absorption layer that absorbs incident light to generate carriers;
Storage means for storing a plurality of photoelectric conversion units having a light-blocking layer between the multiplication layer for multiplying the carrier, and storage means for storing electric signals generated by the plurality of photoelectric conversion units; and the photoelectric conversion unit Scanning means for scanning the electric signals generated by the plurality of photoelectric conversion units, and a signal output unit having at least one means selected from reading means for reading the electric signals generated by the plurality of photoelectric conversion units. A photoelectric conversion device, wherein a plurality of the photoelectric conversion units and the signal output unit are electrically connected. 23. The multiplying layer has a minimum forbidden band width Eg2,
23. The photoelectric conversion device according to claim 22, wherein one or more layers having a step-back structure in which a forbidden band width of a maximum forbidden band width Eg3 continuously changes are stacked. 24. The photoelectric conversion device according to claim 22, wherein the multiplication layer is formed by alternately stacking layers having a high dielectric constant and layers having a low dielectric constant. 25. The photoelectric conversion device according to claim 22, wherein the light absorption layer is made of a non-single-crystal material. 26. The photoelectric conversion device according to claim 22, wherein the multiplication layer is made of a non-single-crystal material. 27. The photoelectric conversion device according to claim 22, further comprising a charge injection blocking layer for preventing unnecessary carriers from being injected into the photoelectric conversion device from outside. 28. The light shielding layer is made of a metal material.
The photoelectric conversion device according to any one of claims 2 to 27. 29. The photoelectric conversion device according to claim 22, wherein the light-shielding layer is a semiconductor material containing a high concentration of impurities. 30. The photoelectric conversion device according to claim 22, wherein a forbidden band width Eg1 of the light absorbing layer is substantially uniform in a layer thickness direction. 31. The photoelectric conversion device according to claim 22, wherein a forbidden band width Eg1 of the light absorbing layer is non-uniform in a layer thickness direction.