JP2001237454A - Semiconductor light-receiving element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an avalanche multiplying type semiconductor light receiving element, whose multiplication factor is high in a low-voltage operation, whose dark current is low at the same time and which is of high sensitivity, and to provide an avalanche multiplying type semiconductor light receiving element which removes the lattice matching condition of an optical absorption layer, and which can expand the range of a material for the optical absorption layer. SOLUTION: In a waveguide semiconductor light-receiving element, an avalanche multiplication layer 12 and optical absorption layers 14, 15 are provided on a semiconductor substrate 1, and one or both of the multiplication layer 12 and the optical absorption layers 14, 15 are sandwiched between a guide layer 11 and a guide layer 16. The concentration of carriers in the optical absorption layers 14, 15 is made higher than the concentration of carriers in the avalanche multiplying layer 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor photodetector, and more particularly to an avalanche multiplication type semiconductor photodetector excellent in low voltage, low noise and high-speed response.

[0002]

2. Description of the Related Art Conventionally, as one type of light receiving element, there is an avalanche multiplication type semiconductor light receiving element in which carriers generated by incident light are multiplied by avalanche phenomenon of a depletion layer to increase light receiving sensitivity. This light receiving element has a characteristic of having a signal amplifying effect, high receiving sensitivity, and excellent high-speed response by combining an avalanche process with a photodiode that detects light using a semiconductor pn junction.

The avalanche process is a process in which a deep reverse bias is applied to a pn junction of a semiconductor to cause ionization of electrons and holes accelerated under a high electric field, and the electrons of the electron-hole pair generated there are generated. The phenomenon of being accelerated again by the high electric field and being ionized is a process that occurs in a chain reaction. The extreme state of this process is avalanche breakdown.
A signal can be amplified using this phenomenon. At this time, since it is necessary to apply a high electric field in order to obtain avalanche multiplication, and it is necessary to secure the layer thickness of the avalanche multiplication layer in order to prevent tunnel breakdown, generally, It is necessary to increase the operating voltage.

On the other hand, Kitano et al. And Hanatani et al. Have proposed that the operating voltage can be reduced by integrating the light absorption layer and the avalanche multiplication layer into a thin film (Kitano et al .:
IEICE Technical Report OPE96-11, p61, (1996-05), Hanatani et al.
-32105 publication etc.). FIG. 4 is a perspective view showing an avalanche multiplication type semiconductor light receiving element capable of reducing an operating voltage. On an n-InP substrate 1, an n-InAlAs layer 2, an InAlGaAs core layer 3, an InAlAs / InG
The aAs superlattice light absorption multiplication layer 4, the InAlGaAs core layer 5, the p-InAlAs layer 6, and the p-InGaAs contact layer 7 are laminated to form a mesa stripe, and these layers 2 to 7 are entirely formed by a polyimide embedding layer 8. Are embedded, a p-type electrode 9 is formed on the polyimide embedding layer 8, and an n-type electrode 10 is formed on the back surface of the n-InP substrate 1.

This semiconductor light receiving element is composed of InGaAs and I
A superlattice structure with nAlAs is used, and the InGaAs layer is used as a light absorbing layer for absorbing the incident light L.
The InGaAs superlattice structure is used as an avalanche multiplication layer. By combining InGaAs and InAlAs, a structure having a large band discontinuity with respect to electrons and a small band discontinuity with respect to holes can be obtained, and the ionization rate of electrons can be improved. Can be achieved. At this time, a waveguide structure is adopted to prevent deterioration of quantum efficiency due to thinning of the light absorbing layer. By using this superlattice structure to form a thin film light absorption layer and an avalanche multiplication layer, low voltage operation is realized.

[0006]

In a conventional avalanche multiplication type semiconductor photodetector, a high electric field is applied to a pn junction to obtain avalanche multiplication, so that the operating voltage is generally high. Therefore, the operating voltage is reduced by integrating the light absorption layer and the avalanche multiplication layer into a thin film and superlattice. By the way, it is theoretically known that when light absorption / photoelectric conversion is performed in the avalanche layer, the excess noise accompanying the avalanche process is further increased, and the excess noise increases and the S / N ratio increases. However, there is a problem that the reception sensitivity is deteriorated.

In order to receive light of 1.3 μm band or 1.5 μm band often used for optical fiber communication, it is necessary to use a material having a small band gap corresponding to this wavelength band for the light absorbing layer. However, when such a material is integrated with the avalanche multiplication layer, a large electric field is applied to the material having a small band gap, which causes a tunnel dark current to be generated. There are problems such as deterioration.

Although the lattice matching between the light absorbing layer and the substrate is considered to be a condition for keeping the dark current small, there is little room for selection of the composition ratio of the compound semiconductor usable as the light absorbing layer. There is a problem that the band gap energy of the layer is limited and cannot be set arbitrarily.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-sensitivity avalanche multiplication type semiconductor photodetector having a high multiplication factor at low voltage operation and a low dark current. It is another object of the present invention to provide an avalanche multiplication type semiconductor light receiving element capable of removing the lattice matching condition of the light absorbing layer and expanding the range of the material of the light absorbing layer.

[0010]

In order to solve the above problems, the present invention provides the following semiconductor light receiving device. That is, the semiconductor light receiving element according to claim 1 of the present invention includes an avalanche multiplication layer and a light absorption layer on a semiconductor substrate,
In a waveguide type semiconductor light receiving device in which one or both of the multiplication layer and the light absorption layer are sandwiched by a guide layer, the carrier concentration of the light absorption layer is set higher than the carrier concentration of the avalanche multiplication layer. It is characterized by:

Further, the semiconductor light receiving element according to claim 2 is
2. The semiconductor light receiving device according to claim 1, wherein an electric field relaxation layer is provided between the avalanche multiplication layer and the light absorption layer.

Further, the semiconductor light receiving element according to claim 3 is
3. The semiconductor light receiving device according to claim 1, wherein the avalanche multiplication layer is formed of a superlattice.

Further, the semiconductor light receiving element according to claim 4 is
The semiconductor light receiving element according to claim 1, 2 or 3,
The carrier concentration of the light absorbing layer has a concentration gradient in the stacking direction.

Further, the semiconductor light receiving element according to claim 5 is
The semiconductor photodetector according to claim 1, wherein the avalanche multiplication layer has a thickness of 0.3 μm.
m or less.

Further, the semiconductor light receiving element according to claim 6 is:
6. The semiconductor light receiving device according to claim 1, wherein the light absorbing layer is formed above the avalanche multiplication layer, and a band gap is arbitrarily set by introducing a strain into the light absorbing layer. It is characterized by having changed to.

In the semiconductor light receiving device according to the present invention, by setting the carrier concentration of the light absorbing layer higher than the carrier concentration of the avalanche multiplication layer, most of the applied voltage is applied to the avalanche multiplication layer. And the voltage applied to the light absorbing layer is very small. As a result, the voltage applied to the light absorbing layer becomes very small, and the operating voltage of the device decreases. Further, when an operating voltage is applied, there is almost no electric field applied to the light absorbing layer, so that a dark current component from the light absorbing layer in an electric field-free state is greatly reduced.

When an electric field relaxation layer is provided between the avalanche multiplication layer and the light absorption layer, the effect of reducing the dark current component from the light absorption layer becomes greater. Further, when the electric field relaxation layer is thinned with a high carrier concentration, the voltage applied to the electric field relaxation layer decreases, which contributes to a reduction in operating voltage as a whole. Further, the light absorbing layer to which no electric field is applied is also excellent in the saturation resistance at the time of high light input, so that large input light can be received effectively.

Here, in order to reduce the operating voltage of the device, a method is employed in which, of the applied voltages represented by the sum of the product of the thickness of each layer and the electric field, the voltage required in the light absorbing layer approaches 0V. Can be In this case, the carrier concentration of the light absorbing layer itself is increased to reduce the electric field, and the operating voltage of the light absorbing layer is reduced by not depleting the entire light absorbing layer. Provide an electric field relaxation layer between them,
The electric field in the avalanche multiplication layer is reduced by the electric field relaxation layer, and the electric field at the interface between the electric field relaxation layer and the light absorption layer is built-in.
There is a method of lowering the operating voltage by using a structure that has a magnitude substantially equal to the electric field due to the potential.

In this case, since the electric field in the light absorption layer is reduced, the efficiency of injection into the avalanche multiplication layer is reduced. Therefore, in order to improve this, by making the dopant concentration, that is, the carrier concentration, have a concentration gradient in the stacking direction inside the light absorption layer, carriers generated by light absorption are injected into the avalanche multiplication layer. It is possible to promote. In addition, since the carrier concentration of the light absorption layer has a concentration gradient in the stacking direction, the efficiency of carrier injection into the avalanche multiplication layer, that is, the photoelectric conversion efficiency (quantum efficiency) is improved.

Further, by making the avalanche multiplication layer a thin film using a superlattice, the operating voltage can be reduced to about 20 V, preferably about 15 V or less. At this time, if the breakdown voltage or the operating voltage is the same as the conventional one, the multiplication factor is the same as the conventional one. On the other hand, since the dark current component from the light absorbing layer is greatly reduced, both the receiving sensitivity and the optimum multiplication factor for achieving the highest sensitivity are improved.

Further, in order to prevent breakdown of tunnel current due to thinning of the avalanche multiplication layer and to maintain breakdown characteristics due to avalanche multiplication, the avalanche multiplication layer is made of a material having a large band gap. Is preferred. When the avalanche multiplication layer is not formed of a superlattice, and when the band gap of the light absorption layer is the same, it is preferable that the band gap of the avalanche multiplication layer be large.

When the light absorbing layer is disposed above the avalanche multiplication layer, strain is introduced into the light absorbing layer, and the band gap of the light absorbing layer is changed by changing the composition of the compound constituting the light absorbing layer. The energy can be adjusted to the energy of the wavelength of the light to be received. Furthermore, by reducing the thickness of the light absorption layer and covering the periphery thereof with a wide gap semiconductor or a material having a low refractive index, a waveguide can be formed, and the quantum efficiency can be increased.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the semiconductor light receiving element of the present invention will be described with reference to the drawings. [First Embodiment] FIG. 1 is a perspective view showing a mesa-type avalanche multiplication type semiconductor light receiving device according to a first embodiment of the present invention. This semiconductor light receiving element is provided on an n-type InP substrate 1.
Guide layer 11, avalanche multiplication layer 12, electric field relaxation layer 1
3, a low-concentration light absorption layer 14, a high-concentration light absorption layer 15, a guide layer 16, and a p-type contact layer 7 are laminated to form a mesa stripe, and these layers 11 to 16 and 7 are entirely formed by a passivation film 17. The passivation film 17 is covered with a p-type electrode 9 electrically connected to the p-type contact layer 7.
Are formed, and an n-type electrode 10 is formed on the back surface of the n-type InP substrate 1.

The conductivity types of these layers, the carrier concentration and the layer thickness which determine the electric field distribution are as follows. Conduction type Carrier concentration (cm ⁻³ ) Layer thickness (μm) Guide layer 11: n 5 × 10e17 0.5 Avalanche multiplication layer 12: n 1 × 10e15 0.3 Electric field relaxation layer 13: p 1 × 10e18 0.05 Low-concentration light absorbing layer 14: p 1 × 10e16 0.1 High-concentration light absorbing layer 15: p 1 × 10e18 0.1 Guide layer 16: p 1 × 10e18 0.5 p-type contact layer 7: p 2 × 10e190 .2

The materials constituting these layers are: a guide layer 11 of InAlGaAs or InGaAsP lattice-matched to InP with an energy gap of １1 eV; an avalanche multiplication layer 12 of InAlAs;
Is InAlAs or InP lattice-matched to InP, and InGaAs in which the low-concentration light absorption layer 14 and the high-concentration light absorption layer 15 are lattice-matched to InP.

The avalanche multiplication layer 12 may have a structure composed of a superlattice in which two types of ultrathin films are stacked in order to improve the ionization ratio. As the superlattice structure at that time, for example, InAlAs (20 nm) / InGa
When a quantum well structure in which AlAs (10 nm) is repeated for 10 periods is used, a multiplication layer having a thickness of about 0.3 μm can be formed.

Since the avalanche multiplication layer 12 is preferably a wide gap semiconductor, a group II-VI compound semiconductor lattice-matched to InP may be used. At this time, the thickness of the electric field relaxation layer 13 is set to about twice (about 0.1 μm) the thickness described above in accordance with the breakdown electric field of the avalanche multiplication layer 12.

In order to fabricate the semiconductor light receiving device, a solid source MBE, a gas source MBE, an MO-MBE capable of utilizing a cracking cell of phosphorus is used as a crystal growth apparatus for growing the layers 11 to 16 and 7. And so on. The growth temperature is between 450 ° C and 520 ° C.
In order to improve the accuracy of the electric field distribution, Be having a small diffusion coefficient is used as the p-type dopant.

First, after forming an epitaxial layer using the above-described crystal growth apparatus, a mesa-stripe waveguide is formed using an etching solution having a composition of Br ₂ : HBr: H ₂ O. At this time, etching is performed so that the substrate 1 is exposed. The size of the mesa forming the waveguide is 5 μm.
It is about mx20 μm. Thereafter, in order to protect the mesa side walls, SiO _x or SiN _x is deposited so as to cover the entire layers 11 to 16 and 7 in a mesa stripe shape, thereby forming a passivation film 17.

The p-type electrode 9 is formed by removing the passivation film 17 at the uppermost portion of the mesa by etching and depositing Ti / Pt / Au. The n-type electrode 10 is made of Au / Ge / Ni
Is formed by vapor deposition using a vacuum vapor deposition device. Note that an antireflection film made of SiN _x or SiO _x is formed on the light incident end face.

Next, the operation of the semiconductor light receiving element will be described. In this semiconductor light receiving element, incident light L, which is an optical signal, is made incident on the light absorbing layers 14 and 15 from the lateral direction, and is matched with the waveguide. Here, the avalanche multiplication is remarkable at about 18 V or more, and the breakdown voltage is about 20 V. At this time, the electric field intensity in the avalanche multiplication layer 12 is about 600 KVcm.
Had become. The maximum multiplication factor of the avalanche multiplication was 30 or more.

The high electric field in the avalanche layer 12 is almost alleviated by the electric field relaxation layer 13, and at the interface between the electric field relaxation layer 13 and the light absorption layer 14, the magnitude is almost the same as the electric field due to the built-in potential. The incident light L incident on this light receiving element passes through the waveguide while being passed through the light absorbing layer 1.
Carriers are generated at 4 and 15. The generated carriers are injected into the electric field relaxation layer 13 and the avalanche multiplication layer 12 to which an electric field is applied due to diffusion and drift, and are detected as optical signals through the multiplication process corresponding to the applied voltage and electric field value in the avalanche multiplication layer 12. Is done.

Here, when the light absorbing layer is composed of two layers of the low concentration light absorption layer 14 and the high concentration light absorption layer 15, a gradient of the carrier concentration is formed in the light absorption layer, and the injection efficiency is improved. I do. This is because an internal electric field is generated due to the carrier concentration gradient, and the recombination loss in the non-depletion layer region can be ignored. The cutoff frequency of this semiconductor light receiving element was about 10 GHz.

FIG. 2 is a diagram showing a band structure of the semiconductor light receiving element. In the figure, reference numeral 21 denotes a low concentration light absorbing layer 1.
A light absorption layer with a concentration gradient constituted by 4 and a high concentration light absorption layer 15, 22 is an n-type contact layer, 23 is a photocarrier (electron), and 24 is a photocarrier (hole). In the drawing, the direction of the layer thickness is the same as the direction of the electric field. When the incident light L is incident on the light absorption layer 21 of the semiconductor light receiving element, electron-hole pairs are generated in the light absorption layer 21, and electrons 23 generated by the electron-hole pairs pass through the electric field relaxation layer 13. Then, it is injected into the avalanche multiplication layer 12. In the avalanche multiplication layer 12, the signal is amplified by avalanche multiplication, so that it can be output as a photocurrent to the outside.

[Second Embodiment] FIG. 3 is a perspective view showing an avalanche multiplication type semiconductor light receiving device according to a second embodiment of the present invention. This semiconductor light receiving element is an n-type InP substrate 1
On top, a guide layer 11, an avalanche multiplication layer 12, an electric field relaxation layer 13, a light absorption layer 31 made of p ⁺ -In _x Ga _{1 -x} As (X is arbitrary), and a buried layer 32 made of p ⁺ -InP
Are formed, and a guide layer 33 and a p-type contact layer 34 are formed on the electric field relaxation layer 13 so as to sandwich the light absorption layer 31 and the buried layer 32. These layers 11 to 13, 31 to 3
4 is entirely covered with a passivation film 17, a p-type electrode 9 conducting to a p-type contact layer 34 is formed on the passivation film 17, and an n-type electrode 10 is formed on the back surface of the n-type InP substrate 1. Is formed.

The conductivity type of these layers, the carrier concentration and the layer thickness which determine the electric field distribution are as follows. Conductivity type Carrier concentration (cm ⁻³ ) Layer thickness (μm) Guide layer 11: n 5 × 10e17 0.5 Avalanche multiplication layer 12: n 1 × 10e15 0.25 Electric field relaxation layer 13: p 1 × 10e18 0.05 Guide layer 33: p 1 × 10e18 0.5 p-type contact layer 34: p 2 × 10e19 0.2

The materials constituting these layers include: a guide layer 11 of InAlGaAs or InGaAsP lattice-matched to InP with an energy gap of １1 eV; an avalanche multiplication layer 12 of InAlAs;
Is InAlAs or InP lattice-matched to InP, the guide layer 33 is InP, and the p-type contact layer 34 is InGa.
As.

In order to fabricate the semiconductor light receiving device, a solid source MBE or a gas source MBE equipped with a phosphorus cracking cell so that phosphorus can be used is used as a crystal growth apparatus for growing the layers 11 to 13 and 31 to 34. , MO-
MBE or the like is used. The growth temperature is 480 ° C. to 53
Between 0 ° C. In order to improve the accuracy of the electric field distribution, Be having a small diffusion coefficient is used as the p-type dopant.

A large mesa stripe portion for forming a waveguide is formed with a size of about 10 μm × 30 μm by using a bromo-based etchant. Further, using a phosphoric acid-based etchant, the middle of the mesa stripe portion is etched into the U-shaped or V-shaped groove up to the electric field relaxation layer 13 to form a groove. The width of this groove is about 5 μm. This groove can be formed by using a dry etching apparatus such as RIBE or RIE.

After pre-growth treatment with a sulfuric acid-based etchant, a light absorbing layer 31 made of p ⁺ -In _x Ga _{1 -x} As (X is arbitrary) is formed using the above-described growth apparatus or MO-VPE apparatus. Then, as the upper buried layer 32, p
By forming ⁺ -InP, the light is confined in the guided mode. After that, SiO _x or SiN _x
Is deposited to form a passivation film 17.

The passivation film 17 in a region necessary for forming the electrode is removed by etching to expose the p-type contact layer 34, and then the p-type electrode 9 is formed. n
The mold electrode 10 is formed by evaporating Au / Ge / Ni using a vacuum evaporator. With the above structure, the optical signal coupled to the waveguide forms an optical carrier in the light absorption layer 31, and the electric field relaxation layer 13, the avalanche multiplication layer 12
Is injected by drift and detected.

Here, the light absorbing layer 31 has p ⁺ -In _x Ga
_{By using 1-x} As (X is an arbitrary value between 1.0 and 0.53), the band gap can be reduced to In smaller than InP.
It can be varied from _0.53 Ga _0.47 As to InAs, and can detect long wavelength light.

This semiconductor light receiving element has a structure different from that of the first embodiment, because InGaAs lattice-matched to InP is deposited on the electric field relaxation layer 13 to form a p-type contact layer 34, Unmatched light absorption layer 3
This is for avoiding the formation of a contact layer on the upper part of the first layer.

In this semiconductor light receiving element, the incident light L, which is an optical signal, is made to enter the waveguide from the lateral direction. This incident light L is incident on the light absorption layer 31 and generates carriers therein. The carriers generated in the absorption target layer 31 reach the electric field relaxation layer 13 by diffusion and are injected into the avalanche multiplication layer 12. When a carrier concentration gradient is formed in the light absorbing layer 31, the injection efficiency is improved. The voltage at which avalanche multiplication is significant is about 15V. The cutoff frequency in this case was about 10 GHz.

As described above, according to the semiconductor light receiving element of each embodiment, the voltage applied to the light absorbing layers 14, 15 (31) can be made extremely small, and the dark current during the avalanche multiplication operation can be reduced. The operating voltage can be reduced while suppressing the increase. Therefore, the multiplication factor is high at low voltage operation, the dark current is low, the sensitivity is high,
By removing the lattice matching condition of the light absorbing layer and expanding the range of the material of the light absorbing layer, an avalanche multiplication type semiconductor light receiving element capable of changing the band gap energy of the light absorbing layer can be provided. In particular, when the operating voltage is set to 15 V or less by using this structure, options for an operating power supply and a signal amplifier circuit are increased, and an optical receiver that is easy to mount and has high sensitivity can be realized.

In the present embodiment, the description has been made mainly on the material on the InP substrate. However, a substrate other than the InP substrate, for example, a GaAs substrate or the like can be used. GaAs
When a substrate is used, each layer is made of a compound lattice-matched to GaAs, and only the light absorbing layer is p ⁺ -In _x Ga _{1 -x} As.
(X is arbitrary). GaSb
System, SiGe mixed crystal system, and Si / Ge heterojunction system. Further, it goes without saying that the light absorbing layer may be a uniform layer having a high concentration or a layer having a concentration gradient over the whole.

[0047]

As described above, according to the semiconductor light receiving device of the present invention, since the carrier concentration of the light absorbing layer is higher than the carrier concentration of the avalanche multiplication layer, most of the applied voltage is increased by the avalanche. Since the voltage is applied to the double layer, the voltage applied to the light absorbing layer can be extremely reduced, and the operating voltage of the device can be reduced. In addition, when an operating voltage is applied, almost no electric field is applied to the light absorbing layer, so that a dark current component from the light absorbing layer in an electric field-free state can be significantly reduced.

Therefore, the multiplication factor is high at low voltage operation,
At the same time, the dark current is low, the sensitivity is high, and the avalanche that can change the band gap energy of the light absorbing layer by removing the lattice matching condition of the light absorbing layer and expanding the range of the material of the light absorbing layer is increased. A double type semiconductor light receiving element can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an avalanche multiplication type semiconductor light receiving element according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a band structure of the avalanche multiplication type semiconductor light receiving element according to the first embodiment of the present invention.

FIG. 3 is a perspective view showing an avalanche multiplication type semiconductor light receiving element according to a second embodiment of the present invention.

FIG. 4 is a perspective view showing a conventional avalanche multiplication type semiconductor light receiving element.

[Explanation of symbols]

 Reference Signs List 1 n-InP substrate 2 n-InAlAs layer 3 InAlGaAs core layer 4 InAlAs / InGaAs superlattice light absorption multiplication layer 5 InAlGaAs core layer 6 p-InAlAs layer 7 p-InGaAs contact layer 8 polyimide burying layer 9 p-type electrode 10 n Type electrode 11 Guide layer 12 Avalanche multiplication layer 13 Electric field relaxation layer 14 Low concentration light absorption layer 15 High concentration light absorption layer 16 Guide layer 17 Passivation film 21 Light absorption layer with concentration gradient 22 n-type contact layer 23 Photocarrier (electron) 24 Photocarrier (hole) 31 Light absorption layer 32 Buried layer 33 Guide layer 34 P-type contact layer L Incident light

Claims (6)

[Claims] 1. A waveguide type semiconductor light receiving device comprising: an avalanche multiplication layer and a light absorption layer on a semiconductor substrate; and one or both of these layers interposed between guide layers. A semiconductor light receiving element wherein the concentration is higher than the carrier concentration of the avalanche multiplication layer. 2. An electric field relaxation layer is provided between the avalanche multiplication layer and the light absorption layer.
The semiconductor light receiving element as described in the above. 3. The semiconductor light receiving device according to claim 1, wherein said avalanche multiplication layer is constituted by a superlattice. 4. The semiconductor light receiving device according to claim 1, wherein a carrier concentration of the light absorbing layer has a concentration gradient in a stacking direction. 5. The thickness of the avalanche multiplication layer is set to 0.1.
The semiconductor light receiving device according to claim 1, wherein the thickness is 3 μm or less. 6. The light absorption layer is formed above the avalanche multiplication layer, and a strain is introduced into the light absorption layer to arbitrarily change its band gap. 6. The semiconductor light receiving element according to any one of claims 5 to 5.