WO2009101740A1 - Semiconductor light receiving element - Google Patents

Abstract

Provided is a light receiving element which is low-cost, does not require an external power supply and absorbs a small quantity of light. The semiconductor light receiving element is of photo-voltage conversion type, and is provided with a semiconductor substrate (101), and a light absorption layer (103) which is formed on the semiconductor substrate (101) and has a multiple quantum well structure of Type-II. In the quantum well structure, a polarization distance is 20nm or more. The optical absorptance of the semiconductor light receiving element is preferably 10% or less.

Description

Semiconductor photo detector

The present invention relates to a semiconductor light receiving element, and relates to a semiconductor light receiving element used in the fields of optical communication and optical interconnection.

Since optical communication is capable of long-distance and large-capacity transmission, long-distance communication has been widely used practically from early on. In recent years, various attempts to use the optical communication as a sensor network have been proposed. For example, it can be considered to be laid along a road network and used as an information communication between road vehicles and an atmospheric gas monitor at an intersection. In addition, laying on large-scale farms, temperature and light sensing are also being considered. In these networks, the light receiving element plays an important role. For example, the light receiving element diagnoses a failure of the sensor network, or supplies power with light to the end of the fiber.

Here, it is desired that the light receiving element applied to the sensor network is low cost and does not require an external power source. Specifically, in order to realize the sensor network as described above, an enormous number of light receiving elements are required, so low cost is an essential condition. Most preferably, the light can be generated from the propagating light itself used for optical communication by the light receiving element without supplying electric power to each sensor.

In general, a light receiving element of a type that converts signal light into a signal current is applied to a semiconductor light receiving element, and a pin type photodiode (PD: Photo Diode) (for example, H. Ishihara, four others, “High-temperature”). aging tests on planar structure InGaAs / InP PIN photodiode with Ti / Pt 」and Ti / Au contact”, Electr on. ｐ Lett, 1984, Vol. 20, No. 16, p. Avalanche photodiode (APD) with gain effect (APD: Avalanche Photo 利得 Diode) (for example, Y. 外 Sugimoto, five others, “High-speed planar-structure InP / InGaA sP / InGaAs avalanche photodiode grown by VPE”, Electron. Lett. 1984, Vol.20, No.16, p.653-654).

In these elements, optical carriers are generated by light absorption in the depleted light absorption layer. Here, it is possible to recognize a signal by drifting with an external electric field and extracting it from the electrode as a current signal. In addition, there are other photoconductive devices that utilize the change in conductivity of the device due to photocarriers generated in the depletion layer (for example, C. Y. Chen and two others, “High-sensitivity Ga0.47In0.53As photoc onductive detectors “prepared” by “vapor” phase “epitaxy”, Appl. “Phys.” Lett., 1984, Vol. 44, p. 1142-1144).

On the other hand, in Japanese Patent Laid-Open No. 2000-216424, a doping dipole structure composed of an n-type high-concentration delta doped layer and a p-type high-concentration delta doped layer close to at least 20 nm or less is periodically formed in an undoped layer that receives light irradiation. A light-voltage conversion type semiconductor light receiving element is disclosed. With such a configuration, a sawtooth band structure is formed, and polarization occurs. As other related techniques, JP-A-62-285476, JP-A-5-160429, JP-A-06-196745, and JP-A-2626309 can be cited.
JP 2000-216424 A JP 62-085476 A Japanese Patent Laid-Open No. 05-160429 Japanese Patent Laid-Open No. 06-196745 Japanese Patent No. 2662309 H. Ishihara, 4 others, “High-temperature aging tests on planar structure InGaAs / InP PIN photodiode with Ti / Pt and Ti / Au contact”, Electr on. Lett., 1984, Vol. 20, no. 16, p. 654-656 Y. Sugimoto, 5 others, “High-speed planar-structure InP / InGaAsP / InGaAs avalanche photodiode grown by VPE”, Electron. Lett., 1984, Vol. 20, no. 16, p. 653-654 C. Y. Chen, two others, “High-sensitivity Ga0.47In0.53As photoc onductive detectors prepared by vapor phase epitaxy”, Appl. Phys. Lett., 1984, Vol. 44, p. 1142-1144

The above-described pin type PD and APD are light-current conversion type light receiving elements, and therefore cannot satisfy the condition that an external power source is unnecessary. The light-voltage conversion type light receiving element disclosed in Japanese Patent Laid-Open No. 2000-216424 does not require an external power supply, but is formed on the InP substrate as a light receiving element having a wavelength of 1 μm, so that the cost is low. It becomes a problem from the viewpoint.

Furthermore, in the sensor network network fault diagnosis application, it is necessary to insert a light receiving element appropriately in the middle of the transmission path. In this case, the light absorption must be small enough not to affect the signal light intensity.

The present invention has been made in view of the above, and an object thereof is to provide a light receiving element that is low in cost, does not require an external power supply, and has low light absorption.

A semiconductor light-receiving element according to the present invention includes a semiconductor substrate and a light absorption layer formed on the semiconductor substrate and having a Type-II multiple quantum well structure, and a polarization distance in the quantum well structure is 20 nm or more. This is a light-voltage conversion type semiconductor light-receiving element.

According to the present invention, it is possible to provide a light receiving element that is low in cost, does not require an external power supply, and has low light absorption.

1 is a perspective view of a light receiving element according to Embodiment 1 of the present invention. FIG. 3 is a cross-sectional view taken along the line IB-IB of the light receiving element according to Embodiment 1 of the present invention. It is a figure explaining the photobol of the Type-I heterostructure of this invention. It is a figure explaining the photovol of Type-II heterostructure of the present invention. It is a figure explaining the structure of the photovol which concerns on this invention. It is sectional drawing which shows the manufacture flow of the light receiving element which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the manufacture flow of the light receiving element which concerns on Embodiment 1 of this invention. It is a perspective view of the light receiving element which concerns on Embodiment 2 of this invention. FIG. 5 is a VB-VB sectional view of a light receiving element according to a second embodiment of the present invention. It is sectional drawing which shows the manufacture flow of the light receiving element which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the manufacture flow of the light receiving element which concerns on Embodiment 2 of this invention.

Explanation of symbols

101, 201 n-type semiconductor substrate 102, 202 n-type buffer layer 103, 203 i-type semiconductor layer 104, 204 p ⁺ -type semiconductor layer 105, 205 Mesa 106, 206 Protective film 107, 207 p-side electrode 108, 208 n-side electrode

Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

Embodiment 1
The configuration of the light receiving element according to Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1A is a perspective view of a light receiving element according to the first embodiment of the present invention. 1B is a cross-sectional view taken along the line IB-IB in FIG. 1A. The light receiving element includes an n-type buffer layer 102, an i-type semiconductor layer 103, a p ⁺ -type semiconductor layer 104, a protective film 106, a p-side electrode 107, and an n-side electrode 108 on an n-type semiconductor substrate 101. In FIG. 1B, the protective film 106 is omitted.

The n-type semiconductor substrate 101 is made of, for example, GaAs.
The n-type buffer layer 102 is formed on the n-type semiconductor substrate 101 and is made of, for example, GaAs.
The i-type semiconductor layer 103 is formed on the n-type buffer layer 102 and has, for example, a Type-II band structure in which three layers of a GaAsSb layer, a GaAs layer, and an InGaAs layer are stacked for 10 periods.
The p ⁺ type semiconductor layer 104 is formed on the i type semiconductor layer 103 and is made of, for example, GaAs.
Here, the n-type buffer layer 102, the i-type semiconductor layer 103, and the p ⁺ -type semiconductor layer 104 constitute a cylindrical mesa 105. As shown in FIG. 1A, light enters from the upper surface of the mesa 105.

The protective film 106 is made of, for example, SiNx, and is formed so as to cover the side surface of the mesa 105 and the upper surface of the n-type semiconductor substrate 101.
The p-side electrode 107 is formed in a ring shape at the edge of the upper surface of the cylindrical mesa 105.
The n-side electrode 108 is formed on the back surface of the n-type semiconductor substrate 101.

The i-type semiconductor layer 103 which is a light absorption layer of the light receiving element according to the first embodiment has a Type-II multiple quantum well structure. 2A and 2B show heterostructures of Type-I and Type-II. In the figure, Ec and Ev are band edges of the conduction band and the valence band, respectively. Eg1 to Eg4 are band gaps. V is an electromotive force voltage generated by polarization. In Type-I, the forbidden band width capable of absorbing light energy is Eg2 or more, whereas in Type-II, it is Eeff. This Eeff is smaller than the forbidden band widths Eg3 and Eg4 of the base material constituting the heterostructure. That is, by using Type-II (staggered type), it is possible to absorb light energy equal to or less than the forbidden band width inherent to the constituent material.

　ここで、Ｑは電荷、Ｃは容量、ｄは分極の距離、εは誘電率、Ｓは面積である。よって、電子と正孔を閉じ込める分極距離が長いほど、また、多周期構造として電荷Ｑを多くすることが、大きな起電力電圧Ｖを得るために有用となる。図３に示すように、隣接したＧａＡｓＳｂ層とＩｎＧａＡｓ層の界面で発生する起電力電圧Ｖは小さい。一方、ＧａＡｓＳｂ層とＩｎＧａＡｓ層との間に形成されたＧａＡｓ層により分極距離ｄが大きくなり、起電力電圧Ｖを大きくすることができる。 Next, the principle of a photovol in which this Type-II heterostructure is laminated in a multi-cycle will be described. FIG. 3 is a band diagram of a structure in which three layers of GaAsSb / GaAs / InGaAs are stacked in a multi-cycle manner. Of course, these materials are only examples. This material has sensitivity to light with a wavelength of 0.9 to 1.3 μm near the heterointerface. Electrons and holes are induced by light irradiation and move to positions where the energy is minimized (at the low energy side in the well layer). Here, since electrons and holes are separated from each other in position, it is the principle of Photobol that voltage is generated by this polarization. This electromotive force voltage V is expressed by the following equation (1).

Here, Q is an electric charge, C is a capacitance, d is a polarization distance, ε is a dielectric constant, and S is an area. Therefore, it is useful to obtain a large electromotive force voltage V as the polarization distance for confining electrons and holes is longer and to increase the charge Q as a multi-period structure. As shown in FIG. 3, the electromotive force voltage V generated at the interface between adjacent GaAsSb layers and InGaAs layers is small. On the other hand, the polarization distance d is increased by the GaAs layer formed between the GaAsSb layer and the InGaAs layer, and the electromotive force voltage V can be increased.

Next, a specifically predicted electromotive force voltage V is calculated. In the Type-II heterostructure, the effective forbidden band width is small, so even the photovolt formed on the GaAs substrate as described above absorbs light having a wavelength of 0.9 to 1.3 μm, which is relatively low energy. can do. On the other hand, since absorption is performed only near the interface, the absorption coefficient can be assumed to be about 30% of the bulk. Now, assuming that the bulk absorption coefficient α is 10000 cm-1, Type-II is 3000 cm-1. Since light absorption with respect to incident light is expressed by exp (−αW), assuming that the absorption width W is 10 nm, the amount of light absorption at one interface is about 0.3% of the incident light.

Next, when the incident light to the light receiving element is 5 mW (= 5 mJ / s), the number of photons per interface / sec is X = 7.8 × 10 12 / sec. Here, assuming that the carrier lifetime τ of the quantum well of Type-II is 100 nsec, the number of carriers N in one quantum well in a steady state is N = 7.8 × 105 from the relationship of N / τ = X. Become. Substituting these calculated data into Equation 1 to obtain the electromotive force voltage, V = 350 mV was obtained. Here, the polarization distance d was 30 nm, and the area S was 10 μm × 10 μm = 100 μm ² . The polarization distance d is preferably 20 nm or more.

This 350 mV electromotive force is a voltage value sufficient to determine the failure of the transmission line. Further, it means that a voltage of 350 mV can be induced at an arbitrary place by light propagation. Therefore, power can be supplied to the sensor. Even when the optical propagation signal performs high-speed transmission exceeding 10 GHz, the photovolt monitor of the present invention does not need to follow the high-speed driving. Power can be supplied.

Furthermore, as described above, in Type-II, the amount of light absorption at one interface is only about 0.3% of the incident light. That is, most light can be transmitted. For this reason, even if it is inserted in any part of the sensor network, it hardly affects the propagation light.

The above point is advantageous in that it monitors the light output of a surface emitting laser that is a multi-mode light emission. Usually, the output mode of a surface emitting laser is not single-peak but multi-peak, and its distribution changes depending on injection current or time. For this reason, a photodetector of the type that monitors part of the light emitted from the surface emitting laser is susceptible to this influence. In the present invention, since the surface emitting laser output can be received as it is and most of the light can pass therethrough, it is possible to monitor the average value of the entire light output. The light absorption rate in the light receiving element is preferably 10% or less.

Next, a method for manufacturing the light receiving element according to Embodiment 1 will be described with reference to FIG. First, as shown in FIG. 4A, on an n-type semiconductor substrate 101 made of GaAs, a Type-II layer in which three layers of a GaAs n-type buffer layer 102, a GaAsSb layer, a GaAs layer, and an InGaAs layer are laminated for 10 periods. The i-type semiconductor layer 103 and the p ⁺ -type semiconductor layer 104 made of GaAs are sequentially laminated by a metal-organic vapor phase epitaxy (MOVPE) method (step 1). Of course, other crystal growth methods such as molecular beam epitaxy (MBE) may be used.

Next, as shown in FIG. 4B, a photoresist is applied onto the p ⁺ type semiconductor layer 104 to form a circular resist mask having a diameter of about 30 μm (step 2). Next, etching is performed by dry etching until the surface of the n-type semiconductor substrate 101 is exposed, and a mesa (columnar structure) 105 having a diameter of about 50 μm is formed (step 3).

Next, a SiNx protective film 106 is formed so as to cover the side surface of the mesa 105 and the surface of the n-type semiconductor substrate 101. Then, the ring-shaped p-side electrode 107 is formed on the top surface of the mesa 105 and the n-side electrode 108 is formed on the back surface of the n-type semiconductor substrate 101, thereby completing the light receiving element of FIG. 1 (step 4).

In the light receiving element according to the first embodiment, an electromotive force voltage of 330 mV was obtained when the incident light was 5 mW. Here, the wavelength of incident light was 1.3 μm.

Embodiment 2
Next, the configuration of the light receiving element according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 5A is a perspective view of a light receiving element according to the second embodiment of the present invention. 5B is a VB-VB cross-sectional view of FIG. 5A. The light receiving element includes an n-type buffer layer 202, an i-type semiconductor layer 203, a p ⁺ -type semiconductor layer 204, a protective film 206, a p-side electrode 207, and an n-side electrode 208 on an n-type semiconductor substrate 201. In FIG. 5B, the protective film 206 is omitted.

The n-type semiconductor substrate 201 is made of, for example, GaAs.
The n-type buffer layer 202 is formed on the n-type semiconductor substrate 201 and is made of, for example, GaAs.
The i-type semiconductor layer 203 is formed on the n-type buffer layer 202 and has a Type-II band structure in which three layers of a GaAsSb layer, a GaAs layer, and a GaAsN layer are stacked for 20 periods.
The p ⁺ type semiconductor layer 204 is formed on the i type semiconductor layer 203 and is made of, for example, GaAs.
Here, the n-type buffer layer 202, the i-type semiconductor layer 203, and the p ⁺ -type semiconductor layer 204 constitute a cylindrical mesa 205. As shown in FIG. 5A, light enters from the end face of the mesa 205.

The protective film 206 is made of, for example, SiNx, and is formed so as to cover the side surface of the mesa 205 and the upper surface of the n-type semiconductor substrate 201.
The p-side electrode 207 is formed on the upper surface of the mesa 205.
The n-side electrode 208 is formed on the back surface of the n-type semiconductor substrate 201.

The photodetector of the first embodiment has a multi-period structure of GaAsSb / GaAs / InGaAs. Since this material system has the same strain direction (compression strain) with respect to the GaAs substrate, if the number of heterointerfaces is increased too much, the critical film thickness will be exceeded, and the crystallinity will deteriorate rapidly. On the other hand, the photodetector of the second embodiment includes a multi-period structure of GaAsSb / GaAs / GaAsN serving as a strain compensation structure. Therefore, the hetero interface can be further increased, the electromotive force voltage V can be further increased, and the light receiving wavelength can be expanded to 0.9 to 1.6 μm.

Next, a method for manufacturing a light receiving element according to the second embodiment will be described with reference to FIGS. First, as shown in FIG. 6A, on an n-type semiconductor substrate 201 made of GaAs, a Type-II in which three layers of an n ⁺ -type semiconductor layer 202 made of GaAs, a GaAsSb layer, a GaAs layer, and a GaAsN layer are stacked for 20 periods. The i type semiconductor layer 203 and the p ⁺ type semiconductor layer 204 made of GaAs are sequentially stacked by MOCVD (step 1). Of course, other crystal growth methods such as molecular beam epitaxy (MBE) may be used.

Next, as shown in FIG. 6B, a photoresist is applied onto the p ⁺ type semiconductor layer 204 to form a stripe resist mask for the waveguide (step 2). Next, etching is performed by dry etching until the surface of the n-type semiconductor substrate 201 is exposed, and a striped mesa 205 having a width of about 30 μm is formed (step 3).

Next, a SiNx protective film 206 is formed so as to cover the side surface of the mesa 205 and the surface of the n-type semiconductor substrate 201. Then, the p-side electrode 207 is formed on the upper surface of the mesa 205 and the n-side electrode 208 is formed on the back surface of the n-type semiconductor substrate 201, thereby completing the light receiving element of FIG. 5 (step 4).

In the light receiving element according to the second embodiment, an electromotive force voltage of 305 mV was obtained when the incident light was 5 mW. Here, the wavelength of incident light was 1.5 μm.

As described above, according to the present invention, it is possible to provide a light receiving element that has sensitivity in the incident light wavelength range of 0.9 to 1.6 μm and does not require an external power supply. Further, an element can be formed on an inexpensive GaAs substrate at a low cost. Since an external power supply is unnecessary, the corresponding circuit can be reduced. Further, since the light absorption layer has a multi-period Type-II heterostructure, the absorption of propagating light can be suppressed to several percent or less. Thereby, there is a merit in a multistage network configuration.

The implementation method of the present invention is not limited to the above-described various forms, and various modifications can be made without departing from the spirit of the present invention. As for the wavelength and material of the light receiving element, those other than those listed in the embodiment can be selected.

This application claims priority based on Japanese Patent Application No. 2008-30821 filed on February 12, 2008, the entire disclosure of which is incorporated herein.

The present invention is a semiconductor light receiving element used in the fields of optical communication and optical interconnection, and can be suitably applied to, for example, a sensor network.

Claims (8)

A semiconductor substrate;
A light absorption layer formed on the semiconductor substrate and having a Type-II multiple quantum well structure;
A light-voltage conversion type semiconductor light receiving element, wherein a polarization distance in the quantum well structure is 20 nm or more. 2. The semiconductor light receiving element according to claim 1, wherein the light receiving wavelength is 0.9 to 1.6 μm. 3. The semiconductor light receiving element according to claim 1, wherein the light absorption rate of the semiconductor light receiving element is 10% or less. 2. The Type-II multiple quantum well structure is formed by periodically laminating a plurality of layers including two layers of an InGaAs layer and a GaAsSb layer, or two layers of a GaAsN layer and a GaAsSb layer. 4. The light receiving element according to any one of items 1 to 3. The Type-II multiple quantum well structure is characterized in that three layers of an InGaAs layer, a GaAsSb layer, and a GaAs layer, or three layers of a GaAsN layer, a GaAsSb layer, and a GaAs layer are periodically stacked. Item 5. The light receiving element according to Item 4. The light receiving element according to any one of claims 1 to 5, wherein the semiconductor substrate is a GaAs substrate. A buffer layer on the semiconductor substrate; and a cap layer;
The light absorption layer is formed between the buffer layer and the cap layer,
7. The semiconductor light receiving element according to claim 1, wherein the semiconductor light receiving element is a surface incident type in which light enters from a direction substantially perpendicular to a main surface of the semiconductor substrate. A buffer layer on the semiconductor substrate; and a cap layer;
The light absorption layer is formed between the buffer layer and the cap layer,
7. The semiconductor light receiving element according to claim 1, wherein the semiconductor light receiving element is of a waveguide type in which light enters from a direction substantially parallel to the main surface of the semiconductor substrate.

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