Semiconductor photodetector

Abstract

To provide a semiconductor photodetector with high sensitivity. [Solution] The semiconductor photodetector comprises an n-type first III-V compound semiconductor layer, a p-type second III-V compound semiconductor layer, a light-absorbing layer provided between the first III-V compound semiconductor layer and the second III-V compound semiconductor layer, and a non-doped third III-V compound semiconductor layer provided between the light-absorbing layer and the second III-V compound semiconductor layer, wherein the light-absorbing layer has a type II superlattice structure, the light-absorbing layer contains an antimony-containing III-V compound semiconductor, and the third III-V compound semiconductor layer contains gallium arsenide antimony or aluminum gallium arsenide antimony.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor light-receiving element.

Background Art

[0002] Patent Document 1 discloses a photodetector. The photodetector includes a substrate having a high transmittance of infrared rays in a desired wavelength region, a type 1 superlattice structure electron barrier layer formed above the substrate and lattice-matched with the substrate, and a type 2 superlattice structure light-receiving layer formed in contact with the electron barrier layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the light-receiving layer contains antimony, the energy of the upper end of the valence band of the light-receiving layer increases. The energy of the upper end of the valence band of the light-receiving layer is greater than the energy of the upper end of the valence band of a p-type contact layer containing indium gallium arsenide (InGaAs). As a result, holes generated in the light-receiving layer are prevented from flowing from the light-receiving layer to the p-type contact layer. Therefore, the sensitivity of the photodetector decreases.

[0005] The present disclosure provides a semiconductor light-receiving element having high sensitivity.

Means for Solving the Problems

[0006] A semiconductor photodetector according to one aspect of the present disclosure comprises an n-type first III-V compound semiconductor layer, a p-type second III-V compound semiconductor layer, a light-absorbing layer provided between the first III-V compound semiconductor layer and the second III-V compound semiconductor layer, and a non-doped third III-V compound semiconductor layer provided between the light-absorbing layer and the second III-V compound semiconductor layer, wherein the light-absorbing layer has a type II superlattice structure, the light-absorbing layer contains an antimony-containing III-V compound semiconductor, and the third III-V compound semiconductor layer contains gallium arsenide antimony or aluminum gallium arsenide antimony. [Effects of the Invention]

[0007] According to this disclosure, a semiconductor photodetector having high sensitivity is provided. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing a semiconductor photodetector according to one embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing the light-absorbing layer included in the semiconductor photodetector shown in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view showing an example of a unit structure contained in the light-absorbing layer of Figure 2. [Figure 4] Figure 4 is a graph showing an example of an energy band diagram of a semiconductor photodetector according to one embodiment. [Figure 5] Figure 5 is a graph showing an example of the energy band diagram of the semiconductor photodetector used in the first experiment. [Figure 6] Figure 6 is a graph showing an example of the relationship between the current of the semiconductor photodetector and the reverse bias voltage in the first experiment. [Modes for carrying out the invention]

[0009] [Description of Embodiments in this Disclosure] First, embodiments of this disclosure will be listed and described.

[0010] (1) The semiconductor photodetector comprises an n-type first III-V compound semiconductor layer, a p-type second III-V compound semiconductor layer, a light-absorbing layer provided between the first III-V compound semiconductor layer and the second III-V compound semiconductor layer, and a non-doped third III-V compound semiconductor layer provided between the light-absorbing layer and the second III-V compound semiconductor layer, wherein the light-absorbing layer has a type II superlattice structure, the light-absorbing layer contains an antimony-containing III-V compound semiconductor, and the third III-V compound semiconductor layer contains gallium arsenide antimony or aluminum gallium arsenide antimony.

[0011] According to the above semiconductor photodetector, the energy at the upper end of the valence band of the III-V compound semiconductor layer becomes greater than the energy at the upper end of the valence band of the light-absorbing layer. As a result, holes generated in the light-absorbing layer can flow from the light-absorbing layer toward the III-V compound semiconductor layer. Therefore, a semiconductor photodetector with high sensitivity can be obtained.

[0012] (2) In the above (1), a p-type fourth III-V compound semiconductor layer may be further provided between the third III-V compound semiconductor layer and the second III-V compound semiconductor layer, and the fourth III-V compound semiconductor layer may contain gallium arsenide antimony or aluminum gallium arsenide antimony.

[0013] In this case, the energy at the top of the valence band of the 4th III-V compound semiconductor layer becomes greater than the energy at the top of the valence band of the 3rd III-V compound semiconductor layer. As a result, holes can flow from the 3rd III-V compound semiconductor layer to the 4th III-V compound semiconductor layer.

[0014] (3) In (2) above, the third III-V compound semiconductor layer may have a thickness greater than the thickness of the fourth III-V compound semiconductor layer.

[0015] (4) In (2) or (3) above, the fourth III-V compound semiconductor layer may include a fifth III-V compound semiconductor layer and a sixth III-V compound semiconductor layer, the fifth III-V compound semiconductor layer may be disposed between the sixth III-V compound semiconductor layer and the third III-V compound semiconductor layer, and the fifth III-V compound semiconductor layer may have a p-type dopant concentration lower than that of the sixth III-V compound semiconductor layer.

[0016] In this case, the gradient of p-type dopant concentration can be reduced in the direction from the 4th III-V compound semiconductor layer to the 3rd III-V compound semiconductor layer.

[0017] (5) Any one of (1) to (4) above may further include a p-type aluminum gallium arsenide antimony layer provided between the second III-V compound semiconductor layer and the third III-V compound semiconductor layer.

[0018] In this case, the p-type aluminum gallium arsenide antimony layer can function as an electron barrier layer.

[0019] [Details of the embodiments of this disclosure] Embodiments of this disclosure will be described in detail below with reference to the attached drawings. In the description of the drawings, the same reference numerals are used for identical or equivalent elements, and redundant descriptions are omitted.

[0020] Figure 1 is a schematic cross-sectional view of a semiconductor photodetector according to one embodiment. Figure 2 is a schematic cross-sectional view of a light-absorbing layer included in the semiconductor photodetector of Figure 1. The semiconductor photodetector 100 shown in Figure 1 is, for example, a photodiode. The semiconductor photodetector 100 comprises an n-type first III-V compound semiconductor layer 12, a p-type second III-V compound semiconductor layer 14, and a light-absorbing layer AD. The light-absorbing layer AD is provided between the first III-V compound semiconductor layer 12 and the second III-V compound semiconductor layer 14. The semiconductor photodetector 100 may also include an indium phosphide (InP) substrate 10. The first III-V compound semiconductor layer 12 may be provided between the InP substrate 10 and the light-absorbing layer AD.

[0021] The semiconductor photodetector 100 includes a non-doped third III-V compound semiconductor layer 16 provided between the light-absorbing layer AD and the second III-V compound semiconductor layer 14. In this specification, "non-doped" means that dopants are not intentionally applied. Therefore, "non-doped" means 1 × 10⁻⁶ 16 cm -3 It may have a p-type dopant concentration of less than 1 × 10⁻⁶. 16 cm -3 It may have an n-type dopant concentration of less than 1.

[0022] The semiconductor photodetector 100 may further include a p-type fourth III-V compound semiconductor layer 18 provided between the third III-V compound semiconductor layer 16 and the second III-V compound semiconductor layer 14. An electron barrier layer EB may be provided between the second III-V compound semiconductor layer 14 and the fourth III-V compound semiconductor layer 18. A hole barrier layer HB may be provided between the first III-V compound semiconductor layer 12 and the light absorption layer AD.

[0023] The InP substrate 10 may be a semi-insulating substrate. The main surface of the InP substrate 10 may be the (100) surface.

[0024] The first III-V compound semiconductor layer 12 is n-type gallium indium arsenide (Ga x In 1-xIt may also be an (InAs or GaInAs) layer. x is the gallium (Ga) composition. x is greater than 0 and less than 1. x may be from 0.46 to 0.48. The n-type dopant concentration in the first III-V compound semiconductor layer 12 is 5×10 17 to 3×10 19 cm -3 and may be such. Examples of n-type dopants include silicon (Si). The thickness of the first III-V compound semiconductor layer 12 may be from 0.2 to 3 μm. The first III-V compound semiconductor layer 12 may be an n-type contact layer. An electrode 30 may be connected to the first III-V compound semiconductor layer 12.

[0025] The second III-V compound semiconductor layer 14 may be a p-type gallium indium arsenide (Ga x In 1-x As or GaInAs) layer. x is the gallium (Ga) composition. x is greater than 0 and less than 1. x may be from 0.46 to 0.48. The p-type dopant concentration in the second III-V compound semiconductor layer 14 is 5×10 17 to 3×10 19 cm -3 and may be such. Examples of p-type dopants include beryllium (Be). The thickness of the second III-V compound semiconductor layer 14 may be from 0.2 to 3 μm. The second III-V compound semiconductor layer 14 may be a p-type contact layer. An electrode 40 may be connected to the second III-V compound semiconductor layer 14.

[0026] The light absorption layer AD has a type-II superlattice structure. The light absorption layer AD may be an undoped III-V compound semiconductor layer. The light absorption layer AD contains a III-V compound semiconductor containing antimony (Sb). The light absorption layer AD may have a thickness greater than the thickness of the first III-V compound semiconductor layer 12 or may have a thickness greater than the thickness of the second III-V compound semiconductor layer 14.

[0027] The third III-V compound semiconductor layer 16 is gallium arsenide antimonide (GaAs y Sb 1-y(Al GaAsSb) or aluminum gallium arsenide antimony (Al z Ga 1-z As y S 1-y It may contain (or AlGaAsSb). z is the aluminum (Al) composition. z may be smaller than the Al composition of the electron barrier layer EB. z may be 0.1 or less. y is the arsenic (As) composition. z and y may be selected to be lattice-matched to InP. The third III-V compound semiconductor layer 16 may have a thickness T1 greater than the thickness T2 of the fourth III-V compound semiconductor layer 18. The thickness T1 of the third III-V compound semiconductor layer 16 may be 300 to 1000 nm.

[0028] The fourth III-V compound semiconductor layer 18 may contain GaAsSb or AlGaAsSb. The fourth III-V compound semiconductor layer 18 may have the same composition as the third III-V compound semiconductor layer 16, except for the dopant. The fourth III-V compound semiconductor layer 18 may contain a fifth III-V compound semiconductor layer 18a and a sixth III-V compound semiconductor layer 18b. The fifth III-V compound semiconductor layer 18a may be placed between the sixth III-V compound semiconductor layer 18b and the third III-V compound semiconductor layer 16. The fifth III-V compound semiconductor layer 18a may have a p-type dopant concentration lower than that of the sixth III-V compound semiconductor layer 18b. In this case, the gradient of the p-type dopant concentration can be reduced in the first direction D1 from the fifth III-V compound semiconductor layer 18a to the sixth III-V compound semiconductor layer 18b. The p-type dopant concentration in the 5th III-V compound semiconductor layer 18a is 1 × 10⁻⁶. 16 From 1 x 10 18 cm -3 It may also be the case that the p-type dopant concentration in the 6th III-V compound semiconductor layer 18b is 5 × 10 17 From 2 x 10 19 cm -3The thickness of the fifth III-V compound semiconductor layer 18a may be 20 to 200 nm. The thickness of the sixth III-V compound semiconductor layer 18b may be 20 to 200 nm. The thickness T2 of the fourth III-V compound semiconductor layer 18 is the sum of the thickness of the fifth III-V compound semiconductor layer 18a and the thickness of the sixth III-V compound semiconductor layer 18b. The thickness T2 of the fourth III-V compound semiconductor layer 18 may be 40 to 400 nm.

[0029] The electron barrier layer EB may be a p-type AlGaAsSb layer. The energy at the lower end of the conduction band of the electron barrier layer EB is greater than the energy at the lower end of the conduction band of the second III-V compound semiconductor layer 14. The electron barrier layer EB prevents electron transfer from the light absorption layer AD to the second III-V compound semiconductor layer 14. The electron barrier layer EB may have a p-type dopant concentration lower than the p-type dopant concentration of the second III-V compound semiconductor layer 14. The p-type dopant concentration in the electron barrier layer EB is 5 × 10⁻⁶. 17 From 2 x 10 19 cm -3 The electron barrier layer EB may have a thickness less than the thickness of the second III-V compound semiconductor layer 14. The thickness of the electron barrier layer EB may be 5 to 1000 nm. The electron barrier layer EB may be a bulk layer. The electron barrier layer EB may not have a superlattice structure and may be a single layer.

[0030] The hole barrier layer HB may be an n-type AlInAs layer. The energy at the top of the valence band of the hole barrier layer HB is lower than the energy at the top of the valence band of the first III-V compound semiconductor layer 12. The hole barrier layer HB prevents the movement of holes from the light absorption layer AD to the first III-V compound semiconductor layer 12. The hole barrier layer HB may have an n-type dopant concentration lower than the n-type dopant concentration of the first III-V compound semiconductor layer 12. The n-type dopant concentration in the hole barrier layer HB is 5 × 10⁻⁶. 17 From 2 x 10 19 cm -3The hole barrier layer HB may have a thickness less than the thickness of the first III-V compound semiconductor layer 12. The thickness of the hole barrier layer HB may be 5 to 50 nm. The hole barrier layer HB may be a bulk layer. The hole barrier layer HB may not have a superlattice structure and may be a single layer.

[0031] A first buffer layer may be provided between the hole barrier layer HB and the first III-V compound semiconductor layer 12. The first buffer layer may be an n-type AlGaInAs layer. The first buffer layer may have different Al and Ga compositions from those of the hole barrier layer HB. The first buffer layer may have a thickness smaller than the thickness of the hole barrier layer HB.

[0032] A second buffer layer may be provided between the hole barrier layer HB and the light absorption layer AD. The second buffer layer may be an undoped AlGaInAs layer. The second buffer layer may have different Al and Ga compositions from those of the hole barrier layer HB. The second buffer layer may have a thickness less than that of the hole barrier layer HB.

[0033] A third buffer layer may be provided between the electron barrier layer EB and the 4th III-V compound semiconductor layer 18. The third buffer layer may be a p-type AlGaAsSb layer. The third buffer layer may have different Al and As compositions from those of the electron barrier layer EB. The third buffer layer may have a thickness smaller than the thickness of the electron barrier layer EB.

[0034] The InP substrate 10, the first III-V compound semiconductor layer 12, the hole barrier layer HB, the light absorption layer AD, the third III-V compound semiconductor layer 16, the fourth III-V compound semiconductor layer 18, the electron barrier layer EB, and the second III-V compound semiconductor layer 14 may be arranged in this order along a first direction D1. The first direction D1 may be perpendicular to the main plane of the InP substrate 10. The first direction D1 may be the thickness direction of the light absorption layer AD. The first direction D1 may be the direction from the first III-V compound semiconductor layer 12 toward the second III-V compound semiconductor layer 14. The first direction D1 may be the crystal growth direction.

[0035] The semiconductor photodetector 100 can detect incident light L. The incident light L may be visible light or infrared light having a wavelength of 0.4 to 4 μm. The incident light L may travel in a first direction D1. The incident light L may pass through the InP substrate 10 and enter the light absorption layer AD. The semiconductor photodetector 100 may have a cutoff wavelength (absorption edge wavelength) of 2 to 4 μm. The semiconductor photodetector 100 can be used in a spectroscopic system, imaging system, or optical communication system of a gas analyzer.

[0036] Figure 2 is a schematic cross-sectional view of the light-absorbing layer included in the semiconductor photodetector shown in Figure 1. As shown in Figure 2, the light-absorbing layer AD comprises a plurality of unit structures U1 stacked in a first direction D1. Adjacent unit structures U1 may be in contact with each other. The number of unit structures U1 may range from 100 to 500. The plurality of unit structures U1 constitute a superlattice.

[0037] Figure 3 is a schematic cross-sectional view showing an example of a unit structure contained in the light absorption layer of Figure 2. As shown in Figure 3, each unit structure U1 is gallium arsenide antimony (GaAs y S 1-y It includes a ) layer L1, an indium arsenide (InAs) layer L2, and a gallium arsenide (GaAs) layer L3. y is the arsenide (As) composition. y is greater than 0 and less than 1. y may be between 0.45 and 0.6. In this case, GaAs y S 1-y Layer L1 can be lattice-matched with the InP layer. GaAsy S 1-y Layer L1, InAs layer L2, and GaAs layer L3 may be stacked in the first direction D1. y S 1-y Layer L1, InAs layer L2, and GaAs layer L3 may be stacked in this order in the first direction D1. In the first direction D1, InAs layer L2 is GaAs y S 1-y It may be provided between layer L1 and GaAs layer L3. Alternatively, GaAs y S 1-y Layer L1, GaAs layer L3, and InAs layer L2 may be stacked in this order in the first direction D1. In the first direction D1, GaAs layer L3 is GaAs y S 1-y It may be provided between layer L1 and InAs layer L2. InAs layer L2 may be in contact with the adjacent GaAs layer L3. GaAs y S 1-y Layer L1 may be in contact with an adjacent layer (InAs layer L2 or GaAs layer L3). A layer located at the end of a first direction D1 in a single unit structure U1 (InAs layer L2 or GaAs layer L3) is in contact with an adjacent GaAs layer in the unit structure U1. y S 1-y It may be in contact with layer L1. GaAs y S 1-y Layer L1 can function as an electron barrier layer or a hole well layer. InAs layer L2 and GaAs layer L3 can function as electron well layers or hole barrier layers.

[0038] In each unit structure U1, the number of pairs containing a single InAs layer L2 and a single GaAs layer L3 is k. k may be from 1 to 10. k may be 2 or more. In this case, the InAs layers L2 and GaAs layers L3 may be arranged alternately. The InAs layers L2 and GaAs layers L3 may be in contact with each other. As shown in Figure 3, GaAs y S 1-y In each of the k pairs on layer L1, the InAs layer L2 and the GaAs layer L3 may be stacked in this order in the first direction D1. Alternatively, GaAs y S 1-yIn each of the k pairs on layer L1, the GaAs layer L3 and the InAs layer L2 may be stacked in this order in the first direction D1.

[0039] InAs layer L2 and GaAs layer L3 are made of GaAs y S 1-y It has a thickness smaller than layer L1. The thickness of InAs layer L2 may be the same as or different from the thickness of GaAs layer L3. GaAs y S 1-y The thickness of layer L1 may be 2.5 to 6.3 nm. The thickness of InAs layer L2 may be 0.2 to 1.6 nm. The thickness of GaAs layer L3 may be 0.2 to 1.5 nm.

[0040] Figure 4 is a graph showing an example of an energy band diagram of a semiconductor photodetector according to one embodiment. According to the semiconductor photodetector 100, as shown in Figure 4, the energy Ev at the upper end of the valence band of the third III-V compound semiconductor layer 16 is greater than the energy Ev at the upper end of the valence band of the light-absorbing layer AD. As a result, holes generated in the light-absorbing layer AD can flow from the light-absorbing layer AD toward the third III-V compound semiconductor layer 16. Holes generated in the light-absorbing layer AD do not remain within the light-absorbing layer AD. Therefore, a semiconductor photodetector 100 with high sensitivity can be obtained.

[0041] If the fourth III-V compound semiconductor layer 18 contains GaAsSb or AlGaAsSb, the energy Ev at the top of the valence band of the fourth III-V compound semiconductor layer 18 becomes greater than the energy Ev at the top of the valence band of the third III-V compound semiconductor layer 16. As a result, holes can flow from the third III-V compound semiconductor layer 16 to the fourth III-V compound semiconductor layer 18. Therefore, the sensitivity of the semiconductor photodetector 100 becomes higher.

[0042] The following describes various experiments conducted to evaluate the semiconductor photodetector 100. The experiments described below are not intended to limit the present invention.

[0043] (Experiment 1) The semiconductor photodetector used in the first experiment has the following configuration, similar to that of semiconductor photodetector 100. InP board 10: InP board, Group III-V compound semiconductor layer 12: n-type GaInAs layer, n-type dopant concentration 1.4 × 10⁻¹⁰ 18 From 1.6 × 10 18 cm -3 , thickness 1.5 μm, Hole barrier layer HB: n-type AlGaInAs layer, Light-absorbing layer AD: A type II superlattice structure, a unit structure including a GaAsSb layer with a thickness of 5 nm, an InAs layer with a thickness of 0.62 nm, and a GaAs layer with a thickness of 0.56 nm (see Figure 3). The number of pairs including the InAs and GaAs layers is 300. III-V compound semiconductor layer 16: Undoped GaAs y S 1-y (y=0.51) layer, thickness 600nm, Group 5III-V compound semiconductor layer 18a: p-type GaAs y S 1-y (y=0.51) layer, p-type dopant concentration 5 × 10 17 cm -3 , thickness 100nm, Group III-V compound semiconductor layer 18b:p-type GaAs y S 1-y (y=0.51) layer, p-type dopant concentration 0.9 × 10 18 From 1.1 × 10 18 cm -3 , thickness 100nm, Electron barrier layer EB: p-type AlGaAsSb layer, p-type dopant concentration 0.9 × 10⁻¹⁶ 18 From 1.1 × 10 18 cm -3 , thickness 180nm, Group III-V compound semiconductor layer 14: p-type GaInAs layer, p-type dopant concentration 0.9 × 10⁻⁶ 19 From 1.1 × 10 19 cm -3 , thickness 200nm.

[0044] (Experimental results) For the semiconductor photodetector used in the first experiment, an energy band diagram was created through simulation, and the relationship between the reverse bias voltage applied to the semiconductor photodetector and the current flowing through it was calculated. The temperature T used in the simulation was 250 Kelvin (K). The simulation results are shown in Figures 5 and 6.

[0045] Figure 5 is a graph showing an example of the energy band diagram of the semiconductor photodetector from the first experiment. In the graph in Figure 5, the horizontal axis represents the position in the thickness direction (first direction D1) of the light-absorbing layer AD. The vertical axis represents energy. In the graph, Ec represents the energy at the lower end of the conduction band, and Ev represents the energy at the upper end of the valence band.

[0046] As shown in Figure 5, in the first experiment, the energy Ev at the top of the valence band of the third III-V compound semiconductor layer 16 is greater than the energy Ev at the top of the valence band of the light-absorbing layer AD.

[0047] Figure 6 is a graph showing an example of the relationship between the current and reverse bias voltage of the semiconductor photodetector in the first experiment. In the graph in Figure 6, the horizontal axis represents the reverse bias voltage (V) applied to the semiconductor photodetector. The vertical axis represents the current (A) flowing through the semiconductor photodetector. The vertical axis is expressed on a logarithmic scale. In the graph, DC represents the dark current and PC represents the photocurrent.

[0048] As shown in Figure 6, when no reverse bias voltage is applied, the dark current decreases while the photocurrent remains high. This can be interpreted as the holes generated in the light-absorbing layer AD flowing smoothly from the light-absorbing layer AD towards the third III-V compound semiconductor layer 16.

[0049] Although exemplary embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments.

[0050] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, not in the sense described above, and all modifications within the sense and scope equivalent to the claims are intended. [Explanation of Symbols]

[0051] 10…InP board 12…Group III-V compound semiconductor layer 14…Second III-V compound semiconductor layer 16…Third III-V compound semiconductor layer 18…4th III-V compound semiconductor layer 18a...VIII-V compound semiconductor layer 18b…6th III-V compound semiconductor layer 30...Electrode 40...electrode 100... Semiconductor photodetector AD... Light-absorbing layer D1…first direction EB…Electron barrier layer HB... Hole barrier layer L…Incoming light L1…GaAs y S 1-y layer L2…InAs layer L3…GaAs layer U1...Unit structure

Claims

1. n-type first III-V compound semiconductor layer, A p-type Group 2III-V compound semiconductor layer, A light-absorbing layer is provided between the first III-V compound semiconductor layer and the second III-V compound semiconductor layer, A non-doped third group III-V compound semiconductor layer is provided between the light-absorbing layer and the second group III-V compound semiconductor layer, Equipped with, The light-absorbing layer has a Type II superlattice structure, The light-absorbing layer comprises a III-V compound semiconductor containing antimony, The third III-V compound semiconductor layer comprises gallium arsenide antimony or aluminum gallium arsenide antimony, and is a semiconductor photodetector.

2. The present invention further comprises a p-type fourth group III-V compound semiconductor layer provided between the third group III-V compound semiconductor layer and the second group III-V compound semiconductor layer, The semiconductor photodetector according to claim 1, wherein the fourth III-V compound semiconductor layer comprises gallium arsenide antimony or aluminum gallium arsenide antimony.

3. The semiconductor photodetector according to claim 2, wherein the third III-V compound semiconductor layer has a thickness greater than the thickness of the fourth III-V compound semiconductor layer.

4. The fourth III-V compound semiconductor layer includes a fifth III-V compound semiconductor layer and a sixth III-V compound semiconductor layer, the fifth III-V compound semiconductor layer being disposed between the sixth III-V compound semiconductor layer and the third III-V compound semiconductor layer. The semiconductor photodetector according to claim 2 or 3, wherein the fifth III-V compound semiconductor layer has a p-type dopant concentration lower than the p-type dopant concentration of the sixth III-V compound semiconductor layer.

5. The semiconductor photodetector according to any one of claims 1 to 3, further comprising a p-type aluminum gallium arsenide antimony layer provided between the second III-V compound semiconductor layer and the third III-V compound semiconductor layer.

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