TWI794398B - Semiconductor light receiving element - Google Patents

Abstract

[Problem] To provide a semiconductor light-receiving element capable of increasing the response speed. [Solution] A back-illuminated semiconductor light-receiving element, comprising a light-absorbing portion near the front surface of a semiconductor substrate transparent to incident light, and having a diameter larger than the light-absorbing portion on the back surface of the semiconductor substrate facing the front surface. And the radius of curvature is the convex lens part of R1, the center of the aforementioned light absorbing part is located on the optical axis of the aforementioned convex lens part, wherein, there is a concave lens part in the central part of the aforementioned convex lens part, and the aforementioned concave lens part and the aforementioned convex lens part share the optical axis, The diameter is smaller than that of the light absorbing portion and the radius of curvature R2 is larger than the radius of curvature R1, and the concave lens portion diffuses incident light toward the light absorbing portion.

Description

Semiconductor light receiving element

The invention relates to a semiconductor light-receiving element that converts received incident light into an electrical signal and outputs it, in particular to a semiconductor light-receiving element that can improve response speed.

In the field of optical communication, in order to cope with the rapid increase in the amount of communication, development to increase the transmission speed is underway. Optical communication is to send optical signals from the sending side through optical fiber cables, etc., and convert the optical signals received by semiconductor light-receiving elements into electrical signals at the receiving side.

The increase in the transmission speed on the receiving side can be achieved by increasing the response speed of the semiconductor light-receiving element, but for this purpose, it is necessary to increase the upper limit of the response speed defined by the element capacitance and element resistance. The smaller the area of the light-receiving part of the semiconductor light-receiving element, that is, the diameter of the light-absorbing part that converts light into electricity (charge), the smaller the capacitance of the element. For example, when realizing a semiconductor light-receiving element with a response frequency band of about 20 GHz , if the diameter of the light absorbing portion is set to be about 20 μm, the element capacitance becomes considerably small.

On the other hand, the semiconductor light receiving element receives incident light, and the incident light is emitted from the end of the optical fiber cable and travels while being diffused at a predetermined spread angle (divergence angle). Accordingly, as the diameter of the light absorbing portion is reduced to reduce the element capacitance, the amount of received light decreases and the receiving efficiency (sensitivity) decreases. Therefore, as described in Patent Documents 1 and 2, for example, there is known a back-illuminated semiconductor light-receiving element in which a convex lens capable of condensing incident light on a small-diameter light-absorbing portion is formed on a semiconductor substrate in order to suppress a decrease in the amount of received light.

[Prior art literature] [Patent Document] Patent Document 1: Japanese Patent No. 2989996 Patent Document 2: Japanese Patent No. 3031238

[Problems to be Solved by the Invention] However, when the convex lens part focuses light on the light absorbing part, charges are concentrated near the focal point, and the movement of the charges is restricted through the space charge effect caused by excessive charge concentration, thereby hindering the improvement of the response speed. High speed. In addition, when the divergence angle of the incident light is small, even if the convex lens part is not focused on the light-absorbing part, the charge generated by the incident light being concentrated on the local part of the light-absorbing part through the light-condensing effect of the convex lens will be excessively concentrated, so there is a problem. There is a possibility that the speed of the response speed will be hindered by the space charge effect.

Even if the divergence angle of the incident light is large, usually in the vertical plane of the central optical axis, the light intensity distribution in the direction of the incident light path is regarded as a Gaussian beam with a Gaussian distribution, and the closer the incident light is to the optical axis, the stronger the intensity. Therefore, the generation of local charges in the light absorbing portion incident on the central portion where the incident light intensity is strong through the light-condensing action of the convex lens portion is excessively concentrated, and the response speed may be hindered by the space charge effect.

An object of the present invention is to provide a semiconductor light-receiving element capable of increasing the response speed.

[Technical means to solve the problem] The invention of claim 1 is a back-illuminated semiconductor light-receiving element, comprising a light-absorbing portion near the front surface of a semiconductor substrate that is transparent to incident light, and having a light-absorbing portion having a diameter ratio of the light-absorbing portion on the back surface of the semiconductor substrate facing the front surface. A convex lens portion with a large portion and a radius of curvature R1, the center of the light absorbing portion is located on the optical axis of the convex lens portion, wherein a concave lens portion is provided at the center of the convex lens portion, and the concave lens portion and the convex lens portion are on the optical axis Commonly, the diameter is smaller than the light absorbing portion and the radius of curvature R2 is larger than the radius of curvature R1, and the concave lens portion diffuses incident light toward the light absorbing portion.

According to the above configuration, the semiconductor light receiving element can condense the light entering the convex lens portion toward the light absorbing portion out of the incident light entering from the rear surface along the optical axis of the convex lens portion, and make it enter the central portion of the convex lens portion. The light in the concave lens portion diffuses toward the light absorbing portion. Therefore, while ensuring the amount of light received by the light absorbing part through light collection, and avoiding the space charge effect caused by the concentration of incident light in the light absorbing part through diffusion, the response speed of the semiconductor light receiving element can be increased. .

The invention of claim 2 is based on the distance L from the exit point of the incident light to the concave lens part, the divergence angle θ of the incident light, the diameter D of the light absorbing part, and the relationship between the concave lens part and the light absorbing part in claim 1. The distance H between them is set to the curvature radius R2 of the concave lens portion so that all the incident light entering the concave lens portion is diffused by the concave lens portion and enters the light absorbing portion.

According to the above configuration, all the light in the central portion where the light intensity of the incident light is strong is diffused and enters the light absorbing portion reliably. Therefore, while ensuring the amount of light received by the light-absorbing portion, avoiding the space charge effect, it is possible to increase the response speed of the semiconductor light-receiving element.

In the invention of claim 3, in claim 2, when the refractive index of the semiconductor substrate relative to air is n, the radius of curvature R1 of the convex lens portion satisfies the following formula: (n-1)/(1/L+n/ H)<R1<(n-1)/(n/H).

According to the above structure, since the light can be collected through the convex lens part without being focused on the light absorbing part, the amount of light received by the light absorbing part can be ensured, and the space charge effect can be avoided, so that the response speed of the semiconductor light receiving element can be increased. change.

According to the invention of claim 4, in claims 1 to 3, the semiconductor substrate is an InP substrate.

According to the above configuration, since infrared light of a wavelength used in optical communication can be efficiently received, the response speed of the semiconductor light receiving element for optical communication can be increased.

[Efficacy of the invention] According to the semiconductor light-receiving element of the present invention, it is possible to increase the response speed.

Hereinafter, the form for implementing this invention is demonstrated based on an Example.

[Example] First, the overall structure of the semiconductor light receiving element 1 will be described based on FIG. 1 . The semiconductor light-receiving element 1 has a semiconductor substrate 2 transparent to incident light, a light-receiving portion 4 disposed near the front surface 3 of the semiconductor substrate 2, a p-electrode 5 on the light-receiving portion 4, and an n electrode 5 on the front surface 3 side of the semiconductor substrate 2. Electrode 6. In addition, the back surface 7 of the semiconductor substrate 2 facing the front surface 3 of the semiconductor substrate 2 is provided with a convex lens portion 8, a concave lens portion 9 having a diameter smaller than the convex lens portion 8 at the central portion of the convex lens portion 8, and at least one covering convex lens portion. The anti-reflection film 10 of the part 8 and the concave lens part 9. Then, a back-illuminated semiconductor light-receiving element 1 is configured, which guides light incident on the convex lens portion 8 and the concave lens portion 9 from the back surface 7 side of the semiconductor substrate 2 into the light-receiving portion 4 and converts it into charges. As the semiconductor substrate 2, an n-InP substrate is used as a light receiving element for receiving infrared light with a wavelength of 1.3 μm or 1.5 μm for optical communication, but an appropriate substrate material can be selected depending on the application.

The front side 3 of the semiconductor substrate 2 is covered, for example, by a buffer layer 11 composed of an n-type InP layer. The light receiving part 4 is composed of a PIN photodiode, and the PIN photodiode is sequentially stacked with a first semiconductor layer composed of, for example, an n-type InP layer on the side of the buffer layer 11 opposite to the semiconductor substrate 2 from the side of the buffer layer 11. 12. A light absorbing part 13 composed of, for example, an n-type InGaAs layer, and a second semiconductor layer 14 composed of, for example, a p-type InP layer. The thicknesses of the buffer layer 11 , the first semiconductor layer 12 , the light absorbing portion 13 , and the second semiconductor layer 14 in this order are, for example, 5 μm, 2 μm, 1 μm, and 2 μm. When obtaining a response frequency band of about 20 GHz, a cylindrical or truncated cone-shaped light receiving part 4 is formed, and the diameter D of the light absorbing part 13 thereof is about 20 μm. In addition, in order to increase the response speed, it is preferable to set the doping concentration of the first and second semiconductor layers 12 and 14 to 1×10 ¹⁸ cm ⁻³ or higher so as to have low resistance.

The p-electrode 5 is arranged to be electrically connected to the second semiconductor layer 14 , and the n-electrode 6 is arranged to be electrically connected to the buffer layer 11 . Areas other than the p-electrode 5 and n-electrode 6 on the front side 3 of the semiconductor substrate 2 may be covered with a protective film (for example, a silicon nitride film with a thickness of about 100 nm, etc.). The electric current generated by the charges generated by the transmitted incident light in the light receiving unit 4 is output to the outside through the p-electrode 5 and the n-electrode 6 .

The convex lens portion 8 on the back surface 7 of the semiconductor substrate 2 is formed into a partial spherical shape with a radius of curvature R1 of 100 μm, and its diameter is larger than that of the light absorbing portion 13, for example, the diameter (width) is 60 μm, and the light of the convex lens portion 8 is arranged. The axis Z passes through the center of the light absorbing portion 13 . A concave lens portion 9 is arranged at the center of the convex lens portion 8 . It has an optical axis Z shared with the convex lens portion 8 and has a partial spherical shape with a curvature radius R2 larger than the curvature radius R1. For example, the concave lens portion 9 has a radius of curvature R2 of 150 μm and a diameter (width) of 5 μm, which are smaller than the diameter of the light absorbing portion 13 , and the distance H between the concave lens portion 13 and the light absorbing portion 13 is 150 μm. Then, on the back surface 7 of the semiconductor substrate 2 , an antireflection film 10 having a thickness of, for example, 100 nm and composed of a silicon nitride film is disposed so as to cover at least the convex lens portion 8 and the concave lens portion 9 . In addition, in FIG. 1 , the concave shape of the concave lens portion 9 is exaggerated for easy viewing.

As shown in FIG. 2 , the incident light entering along the optical axis Z from the back surface 7 side of the semiconductor light receiving element 1 is refracted by the convex lens portion 8 or the concave lens portion 9 and reaches the light absorbing portion 13 . For example, when incident light with a divergence angle 2θ (full angle) of 5° is emitted from a position 50 μm away from the concave lens portion 9 on the optical axis Z, almost all of the incident light enters the concave lens portion 9 . The incident light then travels in such a manner that the concave lens portion 9 is more diffused to reach the light absorbing portion 13 . In addition, as shown by the dotted line, when the divergence angle 2θ of the incident light emitted from the same exit position is larger than 5°, the central part of the incident light near the optical axis Z enters the concave lens 9 and reaches the light absorber in a diffused manner. Section 13. Then, the incident light on the outer side enters the convex lens portion 8 and can pass through the light-condensing effect of the convex lens portion 8 to reach the light absorbing portion 13 .

FIG. 3 shows the simulation results of the arrival position of the light absorbing portion 13 for the incident light having a divergence angle 2θ of 5° emitted from the emission position in FIG. 2 for the semiconductor light receiving element 1 . FIG. 4 shows the simulation results of the arrival position of the same incident light at the light absorbing portion 13 for a conventional semiconductor light receiving element equivalent to the semiconductor light receiving element 1 except for the concave lens portion 9 . The circles in the figure represent the light absorbing portion 13 , and the dots represent the arrival positions of the 500 light rays included in the randomly extracted incident light at the light absorbing portion 13 . It can be seen that in FIG. 4 without the concave lens portion 9, although the light is concentrated at the center of the light absorbing portion 13, the arrival position is not concentrated at the center of the light absorbing portion 13 through the concave lens portion 9 in FIG. Even wider range.

The relationship between the average value and the standard deviation between the divergence angle 2θ of the incident light incident on the semiconductor light receiving element 1 and the distance u between the arrival position of the incident light and the center of the light absorbing portion 13 is shown in FIG. 5 . The squares (□) in the figure represent the average value of the conventional semiconductor light receiving element without the concave lens portion 9, and the circles (○) represent the average value of the semiconductor light receiving element 1 with the concave lens portion 9. Among these average values Arrows extending up and down indicate each standard deviation. When there is no concave lens portion 9 , the smaller the divergence angle 2θ is, the smaller the average value of the distance u is, and the smaller the standard deviation indicating the variation is. On the other hand, in the semiconductor light-receiving element 1 having the concave lens portion 9, the smaller the divergence angle 2θ, the average value of the distance u tends to be larger than that without the concave lens portion 9, and the standard deviation does not become smaller and the deviation larger. Therefore, it can be seen that the incident light diffuses through the concave lens portion 9 and reaches the light absorbing portion 13 .

The setting of the radius of curvature R1 of the convex lens portion 8 will be described based on FIG. 6 . The arc 8a of the radius R1 centered on the point O is a partial spherical surface of the convex lens part 8 representing the radius of curvature R1. On the optical axis Z, the point A of the distance L1 from the arc 8a is used as the exit point, and the arc along the optical axis Z The way to emit light with a divergence angle of 2θ. Let the point where the optical axis Z intersects the arc 8a be set as point B, the point where the outermost ray of the incident light intersects the arc 8a is set as point P, and the point where the incident light is focused on the optical axis Z is set as point C, Then the distance from point B to point C is set as H1. In addition, the incident light is emitted in the air, and the refractive index of air is n1, and the refractive index of the convex lens part 8 is n2, so the refractive index n2 of the convex lens part 8 relative to the refractive index of air n1 is defined as the refractive index n (=n2/n1 ). At this time, the paraxial ray is approximated, and the relationship between the radius of curvature R1 , the distances L1 , H1 , and the refractive index n is expressed by the following formula (1). (1/L1)+(n/H1)=(n-1)/R1...(1)

When the light absorbing part 13 is arranged at point C, if the radius of curvature is set to be greater than the radius of curvature R1 obtained from formula (1) given the refractive index n and the distances L1 and H1, the light-condensing effect of the convex lens part 8 will Therefore, the incident light can be focused so as not to be focused on the light absorbing portion 13 at point C. Therefore, the curvature radius R1 is set so as to satisfy the following expression (2) obtained by modifying the expression (1). R1>(n-1)/(1/L1+n/H1) ... (2)

Similarly, when the light absorbing part 13 is arranged at point C, the incident light is regarded as a bundle of rays parallel to the optical axis Z and the distance L1→∞ is set in formula (1), if the set radius of curvature is smaller than the given refractive index The radius of curvature R1 obtained from n and the distance H1 enhances the light-condensing effect of the convex lens portion 8 , so that incident light that diffuses and travels can be focused on the light-absorbing portion 13 . Therefore, the radius of curvature R1 is set so as to satisfy the following expression (3) obtained by modifying the expression (1). R1<(n-1)/(n/H1) …(3)

Next, setting of the radius of curvature R2 of the concave lens portion 9 will be described based on FIG. 7 . The arc 9a of the radius R2 is a partial spherical surface of the concave lens portion 9 representing the radius of curvature R2. On the optical axis Z of the concave lens portion 9, at a point P0 at a distance L from the arc 9a, the light of the divergence angle 2θ is along the optical axis Z. Way to shoot.

The optical axis Z is set as the x-axis, and the y-axis perpendicular to the x-axis is set with the center of the arc 9a as the origin, and the point at which the light ray IL1 on the outermost side of the incident light enters the concave lens portion 9 at the incident angle α is set to be Point P1, let the refraction angle at point P1 be β. In addition, when the refractive index n2 of the concave lens portion 9 relative to the air refractive index n1 is defined as the refractive index n, the refractive index n=sinα/sinβ according to Senel's law. A point (x2, 0) on the x-axis at a distance H from the concave lens portion 9 in the traveling direction of the incident light is set as a straight line with the length D of the light-absorbing portion 13 representing the diameter D perpendicular to the x-axis centered on this point, The traveling ray IL2 is refracted at the refraction angle β at the point P1, and the point where it crosses the straight line indicating the light absorbing portion 13 is defined as a point P2. The intersection angle between this ray IL2 and the x-axis is set to γ.

When the coordinates of points P0, P1, and P2 are set to P0 (x0, 0), P1 (x1, y1), and P2 (x2, y2), based on the straight line y=(x-x0)tanθ representing the ray IL1 and the ray The straight line y-y1=(x-x1)tanγ of IL2, and these relationships are shown in the following formulas (4) to (11). [mathematical formula 1]

In the equations (4) to (11), if the distance L from the exit point of the incident light to the concave lens part 9, the divergence angle θ (half angle) of the incident light, the diameter D of the light absorbing part 13, and the distance between the concave lens part 9 and the The distance H between the light absorbing parts 13 can be set such that the radius of curvature R2 of the concave lens part 9 is set to be |y2|=D/2 at the point P2 where the light beam IL2 enters the light absorbing part 13 . For example, when L=50 μm, 2θ=5° (θ=2.5°), D=20 μm, and H=150 μm, set R2=150 μm. The concave lens portion 9 with the radius of curvature R2 set in this way diffuses all the light incident on the concave lens portion 9 to the light absorbing portion 13 , thereby reducing the concentration of incident light on the light absorbing portion 13 . Therefore, since the space charge effect due to the concentration of charges generated in the light absorbing portion 13 can be suppressed through the concave lens portion 9 , it is possible to increase the response speed.

Here, the distance L1 between the exit point of the incident light and the convex lens portion 8 is approximately equal to the distance L between the exit point of the incident light and the concave lens portion 9 . In addition, the distance H1 between the convex lens portion 8 and the light absorbing portion 13 is approximately equal to the distance H between the concave lens portion 9 and the light absorbing portion 13 . Accordingly, L1 and H1 in the formulas (2) and (3) can also be regarded as L and H, respectively, and the radius of curvature R1 of the convex lens portion 8 can be set. that is. The curvature radius R1 is set to satisfy the following formula (12), whereby the convex lens portion 8 can focus light on the light absorbing portion 13 without focusing on the light absorbing portion 13 . For example, when L=50 μm, H=150 μm, and n=3.2, set R1=100 μm. (n-1)/(1/L+n/H)<R1<(n-1)/(n/H) ...(12)

Next, a method for forming the semiconductor light-receiving element 1 will be described. As shown in FIG. 8 , on the front side 3 of the cleaned semiconductor substrate 2 , the buffer layer 11 , the first semiconductor layer 12 , the light absorbing portion 13 , and the second semiconductor layer 14 are sequentially formed from the front side 3 side through the vapor phase growth method or the like. film forming. Then, an etching mask 15 is formed on the surface of the second semiconductor layer 14 to cover a predetermined region where the light receiving unit 4 is to be formed. The etching mask 15 is formed by removing, for example, a silicon nitride film formed on the surface of the second semiconductor layer 14 by a selective etching method or the like so that only a predetermined region remains.

Next, as shown in FIG. 9, the second semiconductor layer 14, the light absorbing portion 13, and the first semiconductor layer 12 are removed by selective etching in such a manner that a predetermined portion covered by the etching mask 15 remains and the buffer layer 11 is exposed. After forming the light receiving portion 4 having the light absorbing portion 13 having a diameter D of, for example, 20 μm, the etching mask 15 is removed. In the case of chemical etching, the commonly used etching solution is a mixed solution of hydrogen bromide (HBr) and methanol, but not limited thereto, and a known etching solution can be used. The light receiving portion 4 may also be formed by dry etching.

After removing the etching mask 15 , in order to protect the front side 3 of the semiconductor substrate 2 having the light receiving portion 4 , it is covered, for example, with a protective film (not shown) composed of photoresist or the like. Then, an etching mask 16 is formed on the back surface 7 of the semiconductor substrate 2 to cover a predetermined region where the convex lens portion 8 is to be formed, for example, with a diameter of 80 μm. The etching mask 16 is formed by removing, for example, a silicon nitride film formed on the back surface 7 of the semiconductor substrate 2 by a selective etching method or the like so that only a predetermined region remains.

Next, as shown in FIG. 10 , on the back surface 7 of the semiconductor substrate 2 , a substantially cylindrical region 17 on which the convex lens portion 8 is formed is formed by selective etching so as to protrude from the semiconductor substrate 2 , and then the etching mask 16 is removed. At this time, the above-mentioned etching solution may be used, or the region 17 may be formed by dry etching.

Next, as shown in FIG. 11 , the entire surface of the back surface 7 of the semiconductor substrate 2 is etched through the above-mentioned etching solution to form a partially spherical convex lens portion 8 . At this time, in the corner portion of the substantially cylindrical region 17 that becomes the convex lens portion 8, since it is etched by the two planes (the circular plane and the peripheral surface of the cylinder) that form the corner portion, compared with the plane portion, the etching process is accelerated. Etched and rounded. The part-spherical convex lens portion 8 having a radius of curvature R1 is formed by rounding the corners of the region 17 .

Next, an etching mask 19 covering the back surface 7 of the semiconductor substrate 2 is formed except on the top of the convex lens portion 8 where the concave lens portion 9 is formed. Then, the concave lens portion 9 is formed on the back surface 7 side of the semiconductor substrate 2 by selective etching. The etching mask 19 is formed by removing, for example, a silicon nitride film formed on the back surface 7 of the semiconductor substrate 2 by selective etching or the like, only the top of the convex lens portion 8 , for example, a region with a diameter of 15 μm. Then, the area where the convex lens portion 8 is exposed is etched through the etching solution.

At this time, the etching of the region where the convex lens portion 8 is exposed is also etched in the lateral direction of the convex lens portion 8 covered by the etching mask 19 . At this time, since the central portion of the region where the convex lens portion 8 is exposed is more likely to be supplied with fresh etching solution than the peripheral portion, etching is promoted and rounded. Utilizing this phenomenon, a partially spherical concave lens portion 9 having a set curvature radius R2 is formed (see FIG. 12 ).

Although not shown, an antireflection film 10 made of a silicon nitride film is formed by plasma CVD or the like so as to cover at least the convex lens portion 8 and the concave lens portion 9, and the unillustrated portion on the front surface 3 side of the semiconductor substrate 2 is removed. Protective film, and through a metal film with a laminated structure such as a chromium film, a nickel film, etc. as an adhesive layer, selectively form the p-electrode 5 and the n-electrode 6, and then cut into a predetermined size to obtain the semiconductor light-receiving element 1 of FIG. 1 .

The operation and effect of the semiconductor light-receiving element 1 according to the embodiment will be described. As shown in FIG. 2 , the semiconductor light receiving element 1 can condense the light incident on the convex lens portion 8 to the light absorbing portion 13 , and diffuse the light entering the concave lens portion 9 toward the light absorbing portion 13 to enter the light absorbing portion 13 . Therefore, while ensuring the amount of light received by the light absorbing portion 13 , excessive concentration of charges generated in the light absorbing portion 13 can be suppressed, space charge effects can be avoided, and the response speed of the semiconductor light receiving element 1 can be increased.

In addition, based on the distance L from the exit point of the incident light to the concave lens part 9, the divergence angle θ (half angle) of the incident light, the diameter D of the light absorbing part 13, and the distance H between the concave lens part 9 and the light absorbing part 13, using The relationship of expressions (4) to (11) sets the radius of curvature R2 of the concave lens portion 9 so that all the light entering the concave lens portion 9 is diffused and enters the light absorbing portion 13 reliably. Therefore, the space charge effect can be avoided while securing the amount of light received, and further, the response speed of the semiconductor light receiving element 1 can be increased.

In addition, the convex lens is set based on the distance H between the concave lens portion 9 and the light absorbing portion 13, which is approximately equal to the distance H1 between the convex lens portion 8 and the light absorbing portion 13, and based on the refractive index n of the semiconductor substrate 2 relative to air. The curvature radius R1 of the portion 8 satisfies Expression (12). Therefore, incident light that has not entered the concave lens portion 9 passes through the convex lens portion 8 and is focused on the light absorbing portion 13 , thereby ensuring a received light amount. Furthermore, since the semiconductor substrate 2 is an InP substrate, the response speed of the semiconductor light-receiving element 1 for optical communication can be increased.

The divergence angle and the length of each part mentioned above are examples, but are not limited thereto, and can be appropriately set depending on required performance and the like. In addition, those skilled in the art can implement various modifications to the above-described embodiments without departing from the gist of the present invention, and the present invention also includes such modifications.

1‧‧‧Semiconductor light receiving element 2‧‧‧Semiconductor substrate 3‧‧‧Front 4‧‧‧light receiving part 5‧‧‧p electrode 6‧‧‧n electrode 7‧‧‧Back 8‧‧‧Convex lens part 9‧‧‧Concave lens part 10‧‧‧anti-reflection film 13‧‧‧light absorbing part

FIG. 1 is a cross-sectional view of a semiconductor light-receiving element according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of incident light incident on the semiconductor light receiving element of FIG. 1 . FIG. 3 is a graph showing simulation results of arrival positions of light absorbing portions when incident light with a divergence angle of 5° enters the semiconductor light receiving element of FIG. 1 . FIG. 4 is a graph showing simulation results of the arrival position of the light absorbing portion when incident light with a divergence angle of 5° enters a semiconductor light receiving element having a conventional convex lens. 5 is a graph showing the relationship between the divergence angle of incident light and the distance from the incident position of the light absorbing part to the center of the light absorbing part, the average value and the standard deviation thereof. FIG. 6 is a diagram illustrating the curvature radius R1 of the convex lens portion. FIG. 7 is a diagram illustrating the radius of curvature R2 of the concave lens portion. Fig. 8 is a cross-sectional view showing steps of forming a semiconductor layer in a semiconductor light-receiving element. Fig. 9 is a cross-sectional view showing steps of forming a light receiving portion in a semiconductor light receiving element. Fig. 10 is a cross-sectional view showing a step of forming a convex portion serving as a convex lens in the semiconductor light receiving element. Fig. 11 is a cross-sectional view showing a step of forming a convex lens portion in a semiconductor light-receiving element. Fig. 12 is a cross-sectional view showing a step of forming a concave lens portion in a semiconductor light-receiving element.

1‧‧‧Semiconductor light receiving element

4‧‧‧light receiving part

7‧‧‧Back

8‧‧‧Convex lens part

9‧‧‧Concave lens part

13‧‧‧light absorbing part

Z‧‧‧optical axis

2θ‧‧‧Divergence angle (full angle)

Claims (4)

A semiconductor light-receiving element, which is a back-illuminated semiconductor light-receiving element, has a light-absorbing portion near the front surface of a semiconductor substrate that is transparent to incident light, and ensures the amount of light received by the light-absorbing portion in order to condense the incident light. The back surface of the above-mentioned semiconductor substrate facing the above-mentioned front is equipped with a convex lens part having a diameter larger than the above-mentioned light-absorbing part and a radius of curvature R1, and the center of the above-mentioned light-absorbing part is located on the optical axis of the above-mentioned convex lens part. The central part of the part has a concave lens part, and the above-mentioned concave lens part and the above-mentioned convex lens part share the optical axis, and the diameter is smaller than the above-mentioned light absorbing part, and the curvature radius R2 is larger than the above-mentioned curvature radius R1. Concentration of the incident light in the light-absorbing portion caused by the action causes the incident light to diffuse toward the light-absorbing portion, thereby suppressing the space charge effect caused by the light-condensing action. The semiconductor light-receiving element described in item 1 of the scope of the patent application, wherein, based on the distance L from the exit point of the incident light to the aforementioned concave lens part, the divergence angle θ of the incident light, the diameter D of the aforementioned light-absorbing part, and the relationship between the aforementioned concave lens part and The distance H between the light absorbing parts is set to the curvature radius R2 of the concave lens part so that all the incident light entering the concave lens part is diffused by the concave lens part and enters the light absorbing part. The semiconductor light-receiving element described in claim 2 of the scope of the patent application, wherein when the refractive index of the semiconductor substrate relative to air is n, the radius of curvature R1 of the convex lens portion satisfies the following formula: (n-1)/( 1/L+n/H)<R1<(n-1)/(n/H). The semiconductor light-receiving element according to any one of claims 1 to 3 of the patent claims, wherein the aforementioned semiconductor substrate is an InP substrate.

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