JPH04116977A - Semiconductor photodetector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] In high-speed optical communications, the present invention aims to realize a semiconductor light-receiving element with high sensitivity and high-speed response, which is used in a receiving device that exclusively requires high-speed response. (1) a light absorption layer provided on the first surface of the semiconductor substrate of the first conductivity type, eight layers of the second conductivity type provided on the light absorption layer, and a light absorption layer provided on the first surface of the semiconductor substrate of the first conductivity type; a first electrode formed on the layer; a second electrode provided on a second surface of the semiconductor substrate opposite to the first surface; and a second electrode provided on the first surface of the semiconductor substrate. an incident light window provided at a position lacking the light absorption layer, which is located on the optical path of the incident light from above the first surface; and an incident light window formed between the second surface of the semiconductor substrate and the light absorption layer. and a reflecting mirror that reflects incident light at a predetermined angle smaller than 90 degrees to the light absorption layer below the layer surface of the second conductivity type, and [2] and the above. The present invention provides a semiconductor light-receiving device according to (1), characterized in that the surface of the groove formed by anisotropic etching on the second surface of the semiconductor substrate is a reflective mirror surface.

[Industrial application field]

The present invention relates to a semiconductor light-receiving element that has high-speed response and high sensitivity in high-speed optical communications.

In recent years, as optical communications using optical fibers have become faster and transmission distances have become longer, a receiver for receiving weak optical signals modulated at high speed has become necessary. For this reason, there is a strong demand for the realization of a semiconductor photodetector diode that has high sensitivity and high-speed response as a photodetector.

[Conventional technology]

The conventional technique will be explained using FIG. 5. FIG. 5 is a cross-sectional view of a conventional example, showing a conventional semiconductor light-receiving element (pin diode).On an n-1nP semiconductor substrate 23, an n-1nGaAs light absorption layer 24 and a p-1nP layer 25 are used for incident light. The windows 27^ are formed in this order. The electrode 26 on the light incident surface is formed in a ring shape around the incident light window 27A, and the other electrode 22 is formed of an electrode material laminated on the opposite surface 21 of the n-1nP semiconductor substrate 23.

The incident light 30 enters perpendicularly through the incident light window 27^,
It passes through the p-1nf'S1 region 25 below it and n-1nG
The light reaches the aAs light absorption layer 24, and while passing through that layer, a part of the light is absorbed and detected as a current.

In order to improve the sensitivity of the photodiode, the incident light 30
It is necessary that the light be sufficiently absorbed by the light absorption layer 24.

Therefore, it is necessary to make the light absorption layer 24 thick. However, since the light absorption layer is generally made of a semiconductor material with a high dielectric constant, increasing the thickness of the light absorption layer increases the junction capacitance, and as a result, the responsiveness deteriorates. Therefore, in order to improve responsiveness, the light absorption layer must be made thinner.

In addition, in order to avoid such deterioration of responsiveness, the incident light that has passed through the light absorption layer is transferred to the back surface of the n-1nP semiconductor substrate 23.
1 or the light absorption layer 24 and the n-1nP semiconductor substrate 2
By reflecting it from the superlattice structure provided between the back surface 21 of 3 and absorbing it again into the light absorption layer 24,
Techniques are also being considered to increase the amount of light absorption without increasing the thickness of the light absorption layer.

However, with this technology, the light simply travels back and forth in the direction of the film thickness, so if a thin light absorption layer is used to improve responsiveness, and the light absorption rate decreases, there will not be a sufficient improvement. There wasn't.

[Problem to be solved by the invention]

According to the conventional method described above, sensitivity is improved by making the absorption layer thicker, so deterioration in response cannot be avoided. The increase in the traveling distance of light in the method is only twice as much at most, and especially when the absorption layer is made thinner because a high-speed response is required, the quantum efficiency is small, and therefore a decrease in sensitivity cannot be avoided.

An object of the present invention is to provide a semiconductor light-receiving diode that can maintain high-speed response and improve light-receiving sensitivity by increasing the traveling distance of light in the absorption layer even if the absorption layer is thin and capable of high-speed response. shall be.

[Means to solve the problem]

The present invention achieves the above object by employing the configuration shown below.

The basic structure of the present invention is shown in FIG.

As shown in FIG. 1, the first configuration of the present invention includes a light absorption layer 4 provided on a first surface 9 of a semiconductor substrate 3 of a first conductivity type, and a light absorption layer 4 provided on the light absorption layer 4. a second conductivity type layer 5 provided, a first electrode 6 formed on the second conductivity type layer 5, the light absorption layer 4 of the semiconductor substrate 3, and the second conductivity type layer 5. and a second electrode 6 provided on the second surface 1 opposite to the surface on which the first electrode 2 is provided. from the second surface 1 of the semiconductor substrate 3 and the incident light window 7A provided at a position lacking the light absorption layer 4, which is located on the optical path of the incident light 30 from above the first surface 9. A reflecting mirror 8 is formed between the light absorption layers (4) and reflects incident light to the light absorption layer 4 directly below the second conductivity type layer 5 at a predetermined angle smaller than 90 degrees. It is.

Further, in the second configuration, in the semiconductor light receiving element according to the first configuration, the surface of the groove 1o formed by anisotropic etching on the second surface 1 of the semiconductor substrate 3 is used as the surface of the reflecting mirror 8. It is characterized by -.

[Operation] The operation of the present invention will be explained with reference to FIGS. 1, 2, and 3.

FIG. 1 is a detailed explanatory diagram of the present invention, and FIG. 1a is a plan view thereof, and FIG. 1 is a sectional view thereof.

In the present invention, as shown in FIG.
Second as B! ! It has a structure in which the light is obliquely incident on the light absorption layer 4 directly under the conductivity type layer 5 at a predetermined angle θ smaller than 90 degrees with the light absorption layer.

That is, in the present invention, FIG.
As shown in FIG.
While passing through the light, the light is absorbed and generates electrons and holes proportional to the amount of absorbed light, which is detected as a change in the current of the light receiving element.

When the reflected light 30B is incident on the light absorption layer 4 at an angle θ, the distance jlL through which the reflected light 30B passes through the light absorption layer 4 is L =
Since d/sin θ, the amount of light ψ absorbed while passing through the light absorption layer 4 is ψ= Φ6(1-exp(-λd/sin θ))...
・Given by (1). Here, Φ. is the amount of incident light, and λ is the absorption coefficient. That is, the smaller the incident angle θ of light, the longer the absorption distance #L and the larger the amount of absorbed light.9 The present invention utilizes this principle.

In the prior art, as shown in Figure 2, which explains the operation of the prior art, the angle θ is always 1C/2, and L is d.
be equivalent to.

FIG. 3 is a detailed explanatory diagram of the present invention, in which the absorption distance in the present invention and the absorption layer I11 in the prior art are calculated from the above equation (1) for the case where the thickness of the absorption layer is d.
[This shows the ratio with d.

It is clear that when the angle θ is small, the absorption distance is large compared to the prior art.

In the present invention, the light incident on the front surface of the substrate can be incident on the absorption layer at a small angle θ by the reflecting mirror provided on the back surface of the substrate. As a result of increasing the amount of light emitted, it becomes possible to realize a highly sensitive semiconductor light-receiving element even with a thin absorption layer.

〔Example〕

FIG. 1 is an explanatory diagram of an embodiment of the semiconductor light-receiving device of the present invention.

The structure shown in FIG. 1 is realized using the following method.

On the surface 9 of the (110) n-1nP semiconductor substrate 3 with a thickness of 150 pm, a 2μ-〇n-1nP buffer layer, an InGaAs light absorption layer 4 with a thickness of 0.6μ-, and a thickness of 0
．． 1 μs p-InGaAs light absorption layer 4A and 1 μs thick
The m+ p-1nP layer and the second conductivity type layer 5 are deposited in this order by the qOcVD method.

By providing the p-InGaAs light absorption layer 4A, a pn junction can be formed within the light absorption layer, so that it is possible to avoid the influence on carrier transport that occurs near the heterojunction due to the band structure.

After that, a part with a diameter of 80 μm, for example, which will become a pin diode, is left in a mesa shape, and the above InPJl layer and the above 1n
The GaAs light-absorbing layer 4, 4A and the second conductivity type region 5 of the p-TnP layer are etched.

Subsequently, the portion removed by the etching is etched with n-InP.
Deposit n lower layer and embed.

Furthermore, at a predetermined position on the surface, the direction of the width of 30μ<I
21 excluding the part that becomes the incident light window extending to the emperor.
A nitride film with a thickness of 5ns was deposited on the entire surface, followed by a nitride film with a thickness of 215n- by sputtering, and a nitride film with a thickness of 4300cm was deposited to block light. 11 and a nitride film constituting the incident light window.

After the above steps, a groove with a width of 200μ-1 depth of 70μ- and a cross-sectional shape in the <ITO> direction is formed at a predetermined position on the surface 1 of the n-1nP semiconductor substrate by milling. do.

Thereafter, the (111) plane is exposed by anisotropic etching.

The electrode 2.6 is formed by providing an opening for the electrode in the portion of the nitride film 11 that covers the pin diode, depositing electrode material on both surfaces 1.9 of the nInP substrate by vapor deposition, and patterning this. It is formed. At the same time, an electrode material is also deposited on the surface of the groove 10, and the reflecting mirror 8
form. A dielectric film may be interposed between the electrode material and the semiconductor substrate 3 in the groove 10, thereby preventing the reaction between the semiconductor substrate 3 and the electrode material and improving the reflectance. can.

Since the surface of the reflecting mirror 8 formed by this method is chemically etched, this method can easily form a flat surface without causing damage to the substrate. Furthermore, since the anisotropically etched surface exhibits a fixed geometrical shape determined from the crystal plane, the reflecting mirror 8 can be manufactured in an accurate shape.

In this embodiment, the incident light 30 with a spot diameter of 25 μm is pi
The light enters the semiconductor substrate 3 from the semiconductor substrate surface 9 on the side where the n diode is formed through the nitride film 11.1-InPn lower layer, is reflected by the reflecting mirror 8, and is transmitted to the light absorption layer 4 and the light absorbing layer 4 as reflected light 30B. The light enters the light absorption layer 4 at an angle of . Assuming that the thickness of the light absorbing layer 4 is 0.7 .mu.-, the absorption distance in this case is 2 .mu.m from FIG. 3.

Therefore, the quantum efficiency of the device according to this example is equal to that of a conventional device with an absorbing layer 2μ steel thick.

However, in the device according to this embodiment, when the depletion layer length of the pin junction is 2 μ-, the junction capacitance is reduced by about 7% compared to the conventional device having an absorption layer of 2 μ-thick. That is, even if the quantum efficiency is the same, the junction capacitance can be reduced, so the response of the element is improved.

This is because the relative permittivity of the InGaAs light absorption layer, 13.8, is greater than the relative permittivity of InP, 12.4, so the thinner the light absorption layer is, the smaller the element capacitance becomes.

FIG. 4 is a detailed explanatory diagram of the present invention, showing the effect of improving quantum efficiency when the wavelength of incident light is 1.55 μm.

In Fig. 4, l is a conventional semiconductor light-receiving diode, and J is a conventional semiconductor light-receiving diode in which the absorption distance has been improved to twice the light absorption layer thickness by making the back surface of the substrate a mirror surface and reciprocating the incident light vertically. , K indicate the quantum efficiency with respect to the thickness of the light absorption layer for the semiconductor light receiving diode of this example. At a light absorption layer thickness of 0.7 μm, the quantum efficiency of the conventional semiconductor light-receiving diode is 43%, and that of the improved one is 67%, but according to this embodiment, it reaches 80%. As described above, according to the present invention, sufficient quantum efficiency can be obtained even in a light-receiving element composed of a thin absorption layer with a small junction capacitance.

In addition, in this example, when incident light with a spot diameter of 30 μι enters the light absorption layer at an angle of 20° as reflected light,
Since the light enters the light absorption layer with a wide width of 5 μ-, the density of electrons and holes generated per unit area is lower than that in the case where the light absorption layer absorbs the incident light directly. Therefore, the space charge It is possible to avoid deterioration of responsiveness due to effects.

Furthermore, in this example, the light absorption layer 4 has a diameter of 80 μm.
- defined by a disk of size, its circumference n - summer nP
It is surrounded by 7. Therefore, there is no absorption layer outside the depletion layer region of the pin junction, and even if light is incident around the junction, no electrons or holes are generated outside the depletion layer region.
This has the effect of preventing deterioration of responsiveness due to diffusion. Also,
In such a structure, there is no need to perform a separate step of providing a window for incident light, which simplifies the process. Of course, it is not possible to impose such a definition on the size of the light absorption layer.
This is not an essential requirement of the present invention.

As another method for manufacturing the reflecting mirror according to the present invention, the entire reflecting mirror may be formed by arranging a large number of grooves formed by anisotropic etching and having an isosceles triangular cross-sectional shape smaller than that of the above embodiment. This manufacturing method requires less etching depth, so it can be easily manufactured. Since the reflective mirror manufactured by this method can make the width of the reflected light beam narrower than the width of the incident light beam, it is suitable for realizing a semiconductor light-receiving element that can receive even a wide width of incident light.

Furthermore, in the method for manufacturing a reflecting mirror already described in detail, ion etching with oblique irradiation may be used instead of anisotropic etching. According to ion etching, the cross-sectional shape can be formed relatively freely, for example, in a sawtooth shape, and the angle between the reflecting mirror and the substrate surface can also be freely formed, so an element with high light receiving efficiency can be realized.

Further, the surface of the InP substrate on which the reflecting mirror is provided can be processed by diagonal polishing to form a reflecting surface, and furthermore, the above-mentioned reflecting mirror can be formed on the processed surface. In a reflecting mirror having such a structure, the ratio between the width of the incident light beam and the width of the reflected light beam can be set freely.

Furthermore, the reflecting mirror can also be constructed of a diffraction grating by taking advantage of the fact that incident light of a specific wavelength that enters the diffraction grating is diagonally diffracted at a specific angle. This diffraction grating is produced by etching the substrate surface, ion implantation into the substrate surface,
It is formed by etching a dielectric or metal layered on the surface of a substrate.

This provides an extremely easy manufacturing method.

In the present invention, since the photodetecting section and the reflecting mirror are integrally formed on one substrate, not only can their relative positions be easily and accurately manufactured, but they are also stable against changes in the external environment. . In addition, there are few adjustment parts when coupling with an external optical circuit, and the sensitivity is improved even to light incident perpendicularly to the surface of the semiconductor substrate, so coupling with an external optical circuit can be easily performed. This makes the device easy to handle.

〔Effect of the invention〕

As explained above, according to the present invention, even a pin diode made of a thin light absorption layer has the effect of obtaining high quantum efficiency, so it is possible to provide a semiconductor light receiving diode with high speed response and high sensitivity. , which greatly contributes to improving the performance of optical communication devices.

7 is an n-InP layer, 7A, 27^ is the incident light window, 8 is a reflective mirror, lO is the groove; 11 is a nitride film, 30 is the incident light, 30B is reflected light.

[Brief explanation of drawings]

FIG. 1 is a detailed explanatory diagram of the present invention. FIG. 2 is an explanatory diagram of the operation of the present invention. FIG. 3 is a detailed explanatory diagram of the present invention. FIG. 4 is a detailed explanatory diagram of the present invention. In the sectional view of the conventional example, 1.9.9A, 21 is the semiconductor substrate surface, 2.6.22.
26 is an electrode, 3.23 is a semiconductor substrate, 4.24 is a light absorption layer, 5 is a layer of second conductivity type, (b) 117I construction explanatory diagram of the present invention No. Z circle

Claims (1)

[Claims] [1] First surface (9) of first conductivity type semiconductor substrate (3)
) a light absorption layer (4) provided on the light absorption layer (4);
a second conductivity type layer (5) provided thereon; and a first electrode (6) formed on the second conductivity type layer (5).
), a second electrode (6) provided on a second surface (1) of the semiconductor substrate (3) opposite to the first surface (9); An incident light window ( 7A) is formed between the second surface (1) of the semiconductor substrate (3) and the light absorption layer (4), and directs incident light to the light absorption layer directly under the layer (5) of the second conductivity type. A semiconductor light-receiving element characterized by having a reflecting mirror (8) that reflects light onto a layer (4) at a predetermined angle smaller than 90 degrees. [2] In the semiconductor light-receiving device according to claim 1, the surface of the groove (10) formed by anisotropic etching on the second surface (1) of the semiconductor substrate (3) is the surface of the reflecting mirror (8). A semiconductor light-receiving element characterized by: