JP2002217449A - Horizontal photo acceptance device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a horizontal photo acceptance device having high response speed and high reliability. SOLUTION: At least one groove 5 is formed in a semiconductor layer 3, which is a light absorption layer. On the semiconductor layer 3, a pair of electrodes 4a and 4b are formed as to cross the longitudinal direction of the groove 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fast light receiving element used in a high-speed optical communication field or the like.

[0002]

2. Description of the Related Art Since a horizontal light receiving element can be basically manufactured only by forming a pair of electrodes on a semiconductor surface, it can be manufactured in comparison with a vertical light receiving element which requires a technique of doping impurities.
The manufacturing process is simple. Also, since the parasitic capacitance of the horizontal light receiving element is smaller than that of the vertical light receiving element of the same size,
It can be said that the horizontal light receiving element is excellent also from the viewpoint of high speed. For this reason, recent reports on optoelectronic integrated circuits at academic conferences and the like employ a horizontal light receiving element in consideration of speeding up.

[0003] MSM (meta
l-semiconductor-metal) type photodiodes
EE Trans. Electron Device, vol37, no.1, pp.31-35,1
990 "etc. Conventionally, in a horizontal light receiving element, the electric field becomes weaker as it gets deeper from the semiconductor surface (that is, the electrode), so that the carrier generated in a deep part has a slower traveling speed. Dominated the response speed of the light receiving element, and various measures have been attempted to control this carrier.

For example, as shown in FIG. 8, a semiconductor formed of a material having a large band gap is formed on a semiconductor substrate 101 in order to block carriers generated in a deep part of the semiconductor due to light incidence from reaching the electrodes 104a and 104b. A structure in which one semiconductor layer 102 and a second semiconductor layer 103 serving as a light receiving layer are sequentially laminated has been proposed in the document “J. Appl. Phys. 70 (4), 15, pp. 2435-2448, 1991”. I have. Further, as shown in FIG. 9 (here, the element portion in front of the figure is cut out to show a cross section), the electrode 10
By forming 4a, 104b in the groove 105 formed in the semiconductor layer 103, the electric field in the carrier movement direction is increased even in the deep part of the semiconductor,
A structure that allows holes to run at high speed in deep semiconductors is described in the document “Appl. Phys. Lett. 69 (2), 8, pp. 245-247, 1996”.
It is introduced in.

[0005]

However, these measures still have problems in response speed, reliability, and quantum efficiency (light receiving efficiency) from the viewpoint of practical use.

For example, in a structure in which the electrodes 104a and 104b are formed in the semiconductor layer 103 (FIG. 9), a multilayer structure (typically Au /
When a Ti) electrode is used, the electrode material diffuses into the semiconductor layer from the side of the electrode that contacts the semiconductor (particularly, the side of Au),
The element will be degraded. Furthermore, in the present element structure, unless the electrodes 104a and 104b are formed thickly, a high electric field for causing carriers to travel at high speed cannot be generated in a region from the semiconductor surface to a deep portion, which is practical. Absent.

In order to suppress the injection of carriers generated in the deep part of the semiconductor, in a structure in which a barrier layer 102 having a large band gap is inserted under the light receiving layer 103 (FIG. 8), the thickness of the light receiving layer 103 is substantially reduced. Since the thickness is reduced, there is a problem that the quantum efficiency decreases. Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a horizontal light receiving element having a high response speed.

[0008]

In order to achieve the above object, in the horizontal light receiving element of the present invention, a groove is formed in a light receiving layer, and a pair of electrodes are formed on the upper surface and side surfaces thereof to form a light receiving layer. The response speed of the element is improved by increasing the electric field in the deep part.

That is, in the present invention, at least one groove is formed in a semiconductor layer which is a light absorbing layer, and a pair of electrodes are formed on the semiconductor layer so as to intersect in a longitudinal direction of the groove. It is characterized in that it has a structure in which a groove is formed in the light receiving layer, which is a generation region, and an electrode is formed on the side surface.

In this manner, as shown by the arrow in FIG. 2, by forming an electrode on the side surface of the groove, the electric field along the side surface of the groove can be applied between the adjacent electrodes in the light-receiving layer which has become a protruding portion other than the portion where the groove is formed. Can be generated. Thereby, a high electric field can be obtained in the deep part of the light receiving layer, and the carrier speed can be improved.

On the other hand, if a barrier layer made of a material having a large energy band gap is formed under the light-receiving layer in the groove forming portion, only a carrier having a high traveling speed generated in a shallow region between the barrier layer and the bottom of the groove from the bottom of the groove can be used. Not involved in the operation. Therefore, by adjusting the thickness between the groove bottom and the barrier layer depending on the amount of etching at the time of forming the groove and the thickness of the light receiving layer,
It is possible to suppress the influence of a carrier having a low traveling speed.

As described above, by handling only carriers having a high traveling speed in the groove forming portion and other portions, a lateral light receiving element having a high response speed is realized.

Here, the barrier layer below the light receiving layer may be a semiconductor multilayer mirror made of a material having a large band gap. As a result, not only the effect of preventing the injection of carriers from the substrate to the electrode portion, but also the improvement of quantum efficiency can be achieved.

The present light receiving element is also excellent in the following points in addition to the improvement of the response speed. In this structure, a high electric field can be obtained in a deep portion of the light-receiving layer regardless of the thickness of the light-receiving layer other than where the groove is formed. Therefore, by optimizing the depth, width, and spacing of the grooves in consideration of the process and quantum efficiency, compared to a conventional structure in which only a barrier layer is inserted,
High quantum efficiency can be obtained. Further, in this structure, the electrode side surface does not come into contact with the semiconductor, so that the electrode material does not diffuse in the lateral direction. Therefore, the reliability is higher than the light receiving element having the conventional embedded electrode structure.

Further, the horizontal light receiving element of the present invention can also take the following forms. Typically, a third substrate formed on a semiconductor substrate
The semiconductor device includes one semiconductor layer and a second semiconductor layer which is the light absorbing layer formed on the first semiconductor layer. Typically, the groove is formed with a plurality of linear grooves, and the pair of electrodes is a comb-shaped electrode. These forms are easy to manufacture and have excellent response speed, reliability, and quantum efficiency.

[0016] By forming a pair of Schottky electrodes on the semiconductor layer serving as the light absorbing layer, the semiconductor layer having the MSM structure or the groove having the light absorbing layer formed on the semiconductor layer. By forming a Schottky junction adjustment layer made of a material having a large energy band gap and forming a pair of Schottky electrodes on the Schottky junction adjustment layer, an MSM structure can be obtained.

Further, an n-type and a p-type impurity region are formed in a surface layer of a predetermined portion of the semiconductor layer which is the light absorbing layer in which the groove is formed, and an n-type ohmic electrode and a p-type impurity region are formed in the n-type impurity region. By forming a p-type ohmic electrode in the impurity region, it is possible to have a pin-type structure.

In order to further improve the quantum efficiency, a structure in which a metal mirror layer is formed on a surface of the semiconductor layer, which is the light absorption layer, on a surface opposite to a surface on which the pair of electrodes are formed may be employed. . This can be manufactured by, for example, forming a semiconductor layer or the like as the light absorbing layer on a substrate, removing the substrate, and forming a metal film there.

Further, in order to further improve the quantum efficiency, the pair of electrodes may be made of a material having a high transmittance to the received light.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 Embodiment 1 of the present invention will be described with reference to FIGS. The proportions of the dimensions of the parts in the drawings do not always match those described below.

As shown in the perspective view of FIG. 1, an AlGaAs semiconductor layer 2 and a GaAs semiconductor layer 3 are sequentially stacked on a semi-insulating GaAs substrate 1 using a usual metal organic chemical vapor deposition method. I have. Ga
In the As semiconductor layer 3, a plurality of linear grooves 5 are formed in parallel using a usual wet etching method. The AlGaAs semiconductor layer 2 having a relatively large band gap, which is a carrier blocking layer, has a layer thickness of about 500 nm, and the GaAs semiconductor layer 3, which is a light absorbing layer, has a layer thickness of about 1.5 μm. The groove 5 formed on the GaAs semiconductor layer 3 has a width of 2 μm, a depth of 1 μm, and an adjacent space.
4 μm.

A pair of Schottky electrodes 4a and 4b are formed on the surface of the GaAs semiconductor layer 3 by using a normal vacuum deposition method. The electrodes 4a and 4b are made of Ti / Pt / Au, and have a layer thickness of about 20 nm, about 20 nm, and about 100 nm in the Ti region, the Pt region, and the Au region, respectively. The electrodes 4a and 4b are formed in a comb shape with a mutual electrode spacing and width of about 2 μm. Also,
The length direction of the comb portions of the electrodes 4a and 4b is perpendicular to the length direction of the groove 5, and the length direction of the comb portions of the electrodes 4a and 4b is
5 is formed so as to crawl on the mesa surface. here,
The plane orientation of the substrate and the like are set so that the protruding portions between the grooves 5 have a forward mesa shape. Thus, the electrodes 4a and 4b can be smoothly formed through the grooves 5 and the protrusions by the grooves 5 being slightly opened upward.

In the above structure, the AlGaAs semiconductor layer 2 is formed on the GaAs substrate 1, but instead of the AlGaAs semiconductor layer 2,
A semiconductor multilayer reflector composed of a plurality of pairs of AlGaAs having different compositions may be formed, whereby the quantum efficiency can be further improved. Furthermore, in order to further improve the quantum efficiency, the substrate 1 can be removed and a metal mirror can be formed on the exposed surface.

In the above structure, in order to control the depth of the groove 5, a thin semiconductor layer having a different etching rate is inserted at a predetermined position in the GaAs semiconductor layer 3 so that the depth of the groove is defined. It may be. Such layers, if very thin, have no adverse effect.

In the above structure, the length direction of the electrodes 4a and 4b and the length direction of the groove 5 may be oblique, not perpendicular. The shapes of the electrodes 4a, 4b and the groove 5 may be slightly modified from those shown.

Further, in the above structure, ITO (Indium Tin Oxide), which is a transparent electrode, may be adopted as a material of the electrodes 4a and 4b, whereby more light reaches the light receiving layer and quantum efficiency is improved.

According to the lateral light receiving element having such a structure,
As shown in FIG. 2, a high electric field strength can be obtained even in the depth direction of the groove 5 in the light receiving element. Therefore, the semiconductor layer 3
Since carriers generated in a deep part in the middle can move at high speed, a light receiving element with improved response speed is realized. Furthermore, since the side surfaces of the electrodes 4a and 4b (particularly, the side surfaces of Au of the Ti / Pt / Au electrode) are not in contact with the semiconductor layer, the diffusion of the electrode material into the semiconductor layer is small, and the reliability can be improved.

(Embodiment 2) Next, Embodiment 2 will be described with reference to FIG. Again, the proportions of the dimensions in the figures do not always correspond to those described.

As in the first embodiment, an AlGaAs semiconductor layer 2 is formed on a semi-insulating GaAs substrate 1 by using a usual metal organic chemical vapor deposition method.
And a GaAs semiconductor layer 3 are sequentially laminated. In the GaAs semiconductor layer 3,
A plurality of grooves 5 are formed using a usual wet etching method. AlGaAs semiconductor layer 2 has a thickness of about 500 nm and GaAs semiconductor layer 3
Has a layer thickness of about 1.5 μm. The groove 5 formed on the GaAs semiconductor layer 3 has a width of 2 μm, a depth of 1 μm, and an adjacent interval of 4 μm.

Next, after forming the groove 5, on the GaAs semiconductor layer 3,
The AlGaAs layer 6 is formed using a metal organic chemical vapor deposition method. Here, the thickness of the AlGaAs layer 6 was about 50 nm. Here is Example 1
And different.

On the surface of the regrown AlGaAs semiconductor layer 6, a pair of Schottky electrodes 4a and 4b are formed using a normal vacuum deposition method. Also in this case, the electrodes 4a and 4b are composed of Ti / Pt / Au, and have a layer thickness of about 20 in the Ti region, the Pt region, and the Au region.
nm, about 20 nm and about 100 nm, respectively. Electrodes 4a, 4b
The shape is a comb shape of about 2 μm in both electrode spacing and width. The length direction of the comb portions of the electrodes 4a and 4b and the groove 5
Is formed so that the length direction of the comb portions of the electrodes 4a and 4b crawls on the normal mesa surface of the groove 5. AlG
Since the electrodes 4a and 4b are formed by forming the aAs layer 6, a high Schottky barrier can be obtained, and dark current can be reduced.

In Example 2, the carrier blocking layer AlGaA
s Instead of a semiconductor layer, a semiconductor multilayer reflector made of AlGaAs with a different composition is formed, a thin semiconductor layer with a different etching rate to control the depth of the groove is inserted, The length direction may be inclined. Further, a transparent electrode IT0 may be employed as the electrode material.

[0034] Even in a horizontal light receiving element having such a structure,
As in the first embodiment, a high electric field strength can be obtained also in the depth direction of the groove in the light receiving element. Therefore, carriers generated in a deep portion in the semiconductor layer can move at a high speed, so that a light receiving element with an improved response speed is realized. Furthermore, since the electrode side surface is not in contact with the semiconductor layer,
The diffusion of the electrode material into the semiconductor layer is small, and the reliability can be improved.

Third Embodiment Next, a third embodiment will be described with reference to FIGS. FIG. 5 is a cross-sectional view of the groove 5 in FIG. 4 along the direction in which the groove 5 extends. Again, the proportions of the dimensions in the figures do not always correspond to those described.

In Example 3, an AlGaAs semiconductor layer 2 and a GaAs substrate 1 were formed on a semi-insulating GaAs substrate 1 by using a usual metal organic chemical vapor deposition method.
s semiconductor layers 3 are sequentially laminated. A plurality of trenches 5 are formed in the GaAs semiconductor layer 3 by using a usual wet etching method. AlGaAs semiconductor layer 2 is about 500n thick
m, the GaAs semiconductor layer 3 has a layer thickness of about 1.5 μm. The groove 5 formed on the GaAs semiconductor layer 3 has a width of 2 μm, a depth of 1 μm, and an adjacent space.
4 μm.

Further, as shown in FIG. 5, an n-type implanted region 7a is formed by ion-implanting Si, and a p-type implanted region 7b is formed by implanting Be in the electrode formation portion of the GaAs semiconductor layer 3. ing. Then, an n-type ohmic electrode 8a is formed on the n-type implanted region 7a, and a p-type ohmic electrode 8b is formed on the p-type implanted region 7b, using a normal vacuum deposition method. The n-type ohmic electrode 8a is made of AuGe / Ni, and the p-type ohmic electrode 8b is made of AuZn. This is a feature of this embodiment. The electrodes 8a and 8b are formed in a comb shape with a mutual electrode spacing and width of about 2 μm. Also, the electrodes 8a,
The length direction of the comb portion of 8b and the length direction of the groove 5 are perpendicular to each other, and the length direction of the comb portion of the electrodes 8a and 8b is formed so as to crawl on the forward mesa surface of the groove 5.

In the structure of the present embodiment, the A1 GaAs semiconductor layer 2 of the carrier block layer is formed on the GaAs substrate 1, but a semiconductor multilayer reflector made of AlGaAs having a different composition may be formed instead. Thereby, the quantum efficiency can be further improved. Further, in order to control the depth of the groove, a thin semiconductor layer having a different etching rate is inserted at a predetermined position in the GaAs semiconductor layer, or the length direction of the comb portion of the electrode is perpendicular to the length direction of the groove. Instead, it may be oblique.

Also in the lateral light receiving element having such a pin type structure, high electric field strength can be obtained in the depth direction of the groove in the light receiving element as in the first embodiment. Therefore, carriers generated in a deep portion in the semiconductor layer can move at a high speed, so that a light receiving element with an improved response speed is realized. Further, since the side surface of the electrode is not in contact with the semiconductor layer, diffusion of the electrode material into the semiconductor layer is small, and reliability can be improved.

Fourth Embodiment Next, a fourth embodiment will be described with reference to FIG. Again, the dimensions and proportions of the drawings do not always match those described.

In the fourth embodiment, an InP semiconductor layer 10 and a GaInA
s semiconductor layers 11 are sequentially laminated. GaInAs
A plurality of grooves 5 are formed in the semiconductor layer 11 by using a usual wet etching method. InP semiconductor layer 10 has a thickness of about 50
The GaInAs semiconductor layer 11 has a thickness of about 1.5 μm. GaInA
The groove 5 formed on the s semiconductor layer 11 has a width of 2 μm, a depth of 1 μm,
It has an adjacent distance of 4 μm. Further, a pair of Schottky electrodes is formed on the surface of the GaInAs semiconductor layer 11 by using a normal vacuum deposition method.
4a and 4b are formed. The electrodes 4a and 4b are made of Ti / Pt / Au, and have a layer thickness of about 20 nm, about 20 nm, and about 100 nm in the Ti region, the Pt region, and the Au region, respectively. Electrode 4
The shapes of a and 4b are formed in a comb shape with both electrode spacing and width being about 2 μm. The length direction of the comb portions of the electrodes 4a and 4b is perpendicular to the length direction of the groove, and the length direction of the comb portions of the electrodes 4a and 4b is formed so as to crawl on the forward mesa surface of the groove.

In the above structure, the InP semiconductor layer 10 which is a block layer is formed on the InP substrate 9, but instead, a semiconductor multilayer reflector made of AlInAs having a different composition may be formed. The quantum efficiency can be further improved. Further, in order to control the depth of the groove, a thin semiconductor layer having a different etching rate may be inserted at a predetermined position in the GaInAs semiconductor layer. The length direction of the electrode and the length direction of the groove may not be perpendicular but may be oblique. Also, IT0, which is a transparent electrode, may be employed as an electrode material, thereby improving quantum efficiency.

With the lateral light receiving element having such a material structure, high electric field strength can be obtained also in the depth direction of the groove in the light receiving element, as in the first embodiment. Therefore, carriers generated in a deep portion in the semiconductor layer can move at a high speed, so that a light receiving element with an improved response speed is realized. Further, since the side surface of the electrode is not in contact with the semiconductor layer, diffusion of the electrode material into the semiconductor layer is small, and reliability can be improved.

Fifth Embodiment Next, a fifth embodiment will be described with reference to FIG. Again, the proportions of the dimensions in the figures do not always correspond to those described.

In the same manner as in Example 4, a semi-insulating InP substrate 9 is formed on an InP semiconductor layer 10 and a G
aInAs semiconductor layers 11 are sequentially stacked. GaInAs semiconductor layer 11
Next, a plurality of grooves 5 are formed using a usual wet etching method. The InP semiconductor layer 10 has a thickness of about 500 nm, and the GaInAs semiconductor layer 11 has a thickness of about 1.5 μm. The groove 5 formed on the GaInAs semiconductor layer 11 has a width of 2 μm, a depth of 1 μm, and an adjacent interval of 4 μm. After the groove 5 is formed, InP 12 is formed on the GaInAs semiconductor layer 11 by using a metal organic chemical vapor deposition method. Where InP
The layer thickness of 12 was about 50 nm. Example 5 and Example 4 differ in this point. InP12 has the same function as the AlGaAs layer 6 of Example 2, and a high Schottky barrier can be obtained.

A pair of Schottky electrodes 4a and 4b are formed on the surface of the regrown InP semiconductor layer 12 using a normal vacuum deposition method. The electrodes 4a and 4b are made of Ti / Pt / Au, and have thicknesses of about 20 nm, about 20 nm, and about 100 nm, respectively, in the Ti region, the Pt region, and the Au region. The shape of the electrodes 4a and 4b is formed in a comb shape with both electrode spacing and width being about 2 μm. The length direction of the comb portions of the electrodes 4a and 4b is perpendicular to the length direction of the groove 5, and the length direction of the electrodes 4a and 4b is formed so as to crawl on the forward mesa surface of the groove 5.

In the structure of the present embodiment, the InP semiconductor layer 10 is formed on the InP substrate 9, but a semiconductor multilayer reflector made of AlInAs having a different composition may be formed instead. Can be further improved. In order to control the depth of the groove, a thin semiconductor layer having a different etching rate may be inserted at a predetermined position in the GaInAs semiconductor layer. The length direction of the electrode and the length direction of the groove may not be perpendicular but may be oblique. You may employ ITO which is a transparent electrode as an electrode material.

[0048] Even in a horizontal light receiving element having such a structure,
As in the first embodiment, a high electric field strength can be obtained also in the depth direction of the groove in the light receiving element. Therefore, carriers generated in a deep portion in the semiconductor layer can move at a high speed, so that a light receiving element with an improved response speed is realized. Furthermore, since the electrode side surface is not in contact with the semiconductor layer,
The diffusion of the electrode material into the semiconductor layer is small, and the reliability can be improved.

[0049]

As described above, the horizontal type light receiving device of the present invention has a structure in which a groove is formed in the light receiving layer which is a carrier generation region and an electrode is formed on the side surface thereof. A light-receiving element having high sensitivity, high reliability, and high response speed can be realized. Such a light receiving element exhibits an excellent effect in a high-speed optical communication field or the like.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view illustrating an MSM-type lateral light receiving element using a GaAs substrate according to a first embodiment.

FIG. 2 is a perspective view showing an electric field of the MSM type lateral light receiving element shown in FIG.

FIG. 3 is a partial cross-sectional view showing Example 2 which is an MSM-type lateral light receiving element using a GaAs substrate.

FIG. 4 is a partial cross-sectional view illustrating a pin-type lateral light receiving element using a GaAs substrate according to a third embodiment.

5 is a partial cross-sectional view of the horizontal light receiving element shown in FIG. 4 along a length direction of a groove.

FIG. 6 is a partial cross-sectional view showing Example 4 which is an MSM-type horizontal light receiving element using an InP substrate.

FIG. 7 is a partial cross-sectional view showing Example 5 which is an MSM-type lateral light receiving element using an InP substrate.

FIG. 8 is a diagram illustrating a conventional example of an MSM-type horizontal light receiving element.

FIG. 9 is a diagram showing another conventional example of an MSM-type horizontal light receiving element.

[Explanation of symbols]

 1 GaAs substrate 2 A1GaAs layer 3 GaAs light-receiving layer (light absorption layer) 4a, 4b Schottky electrode 5 groove 6 AlGaAs layer (Schottky junction adjustment layer) 7a n-type injection region 7b p-type injection region 8a n-type ohmic electrode 8b p Type ohmic electrode 9 InP substrate 10 InP layer 11 GaInAs light receiving layer (light absorption layer) 12 InP layer (Schottky junction adjustment layer)

Claims (11)

[Claims] A horizontal type wherein at least one groove is formed in a semiconductor layer which is a light absorbing layer, and a pair of electrodes are formed on the semiconductor layer so as to intersect in a longitudinal direction of the groove. Light receiving element. 2. The semiconductor device according to claim 1, further comprising a first semiconductor layer formed on the semiconductor substrate, and a second semiconductor layer serving as the light absorbing layer formed on the first semiconductor layer. The horizontal light receiving element as described in the above. 3. The horizontal light receiving element according to claim 1, wherein the groove has a plurality of linear grooves. 4. The horizontal light receiving element according to claim 1, wherein the pair of electrodes is a comb-shaped electrode. 5. The horizontal light receiving device according to claim 1, wherein a pair of Schottky electrodes are formed on the semiconductor layer serving as the light absorbing layer to have an MSM type structure. element. 6. A Schottky junction adjustment layer made of a material having a large energy band gap is formed on a semiconductor layer which is the light absorption layer in which the groove is formed,
5. The horizontal light receiving element according to claim 1, wherein a pair of Schottky electrodes are formed on the Schottky junction adjustment layer to have an MSM type structure. 7. An n-type and p-type impurity region is formed in a surface layer of a predetermined portion of the semiconductor layer which is the light absorption layer in which the groove is formed, and an n-type ohmic electrode and a p-type impurity region are formed in the n-type impurity region. By forming a p-type ohmic electrode in the impurity region,
5. The horizontal light-receiving element according to claim 1, having an in-type structure. 8. The horizontal light receiving device according to claim 2, wherein the first semiconductor layer is made of a material having an energy band gap larger than a material of the second semiconductor layer. element. 9. The horizontal light-receiving element according to claim 2, wherein the first semiconductor layer is constituted by a semiconductor multilayer mirror. 10. The semiconductor device according to claim 1, wherein a metal mirror layer is formed on a surface of the semiconductor layer, which is the light absorption layer, on a surface opposite to a surface on which the pair of electrodes are formed. Horizontal light receiving element. 11. The device according to claim 1, wherein the pair of electrodes are made of a material having a high transmittance to received light.
11. The horizontal light-receiving element according to any one of items 1 to 10.