Semiconductor photodetector

Abstract

To provide a semiconductor light-receiving element that can suppress deterioration in sensitivity.SOLUTION: A semiconductor light-receiving element 1 comprises a top surface 1a, a light absorption film 21 of a first conductivity type, a first cap layer 22 of the first conductivity type which is laminated on the light absorption film 21 and has larger band gap energy than the light absorption film 21, and a doping region 30 which is formed extending from the top surface 1a toward the first cap layer 22, and has a second conductivity type. The doping region 30 includes a plurality of parts 31 which are opposed across a gap 30g when viewed from a first direction crossing the top surface 1a, and the gap 30g has a width G30 larger than a thickness T22 of the first cap layer 22 in the first direction.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 describes a light receiving element. This light receiving element includes a light absorption layer that absorbs incident light and converts it into an electrical signal, a cap layer formed on the light incident side of the light absorption layer and having a larger energy band gap than the light absorption layer, and a contact layer formed around the light receiving surface of the cap layer, made of the same material as the light absorption layer and thicker than the cap layer. Further, in this light receiving element, impurities are doped at a high concentration near the interface between the light absorption layer and the cap layer, and in the cap layer and the contact layer, whereby a P + type high-concentration impurity region is formed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the light receiving element described in Patent Document 1, it is considered that a high-concentration impurity region is formed over the entire light receiving surface in the light absorption layer and the cap layer. In this case, since light of a wavelength absorbed in the high-concentration impurity region is not signaled and extracted, there is a risk of loss and a decrease in sensitivity.

[0005] An object of the present disclosure is to provide a semiconductor light receiving element capable of suppressing a decrease in sensitivity.

Means for Solving the Problems

[0006] The semiconductor photodetector according to this disclosure is [1] "a semiconductor photodetector comprising: a surface that receives incident light; a first semiconductor layer having a first conductivity type; a second semiconductor layer having a first conductivity type and laminated on the first semiconductor layer on the surface side of the first semiconductor layer, having a bandgap energy greater than the bandgap energy of the first semiconductor layer; and a doping region having a second conductivity type different from the first conductivity type and extending from the surface toward the second semiconductor layer and reaching at least into the interior of the second semiconductor layer, wherein the thickness of the second semiconductor layer in a first direction intersecting the surface is thinner than the thickness of the first semiconductor layer in the first direction, and the doping region includes a plurality of portions facing each other with a gap between them when viewed from the first direction, and the width of the gap is greater than the thickness of the second semiconductor layer in the first direction."

[0007] In the semiconductor photodetector described in [1] above, a second semiconductor layer of the first conductivity type with a large bandgap energy is stacked on a first semiconductor layer of the first conductivity type, forming a doping region of the second conductivity type that extends from the surface receiving incident light towards the second semiconductor layer. The doping region includes multiple portions that face each other across a gap when viewed from a first direction intersecting the surface. Therefore, light incident on the gap in the doping region can be extracted as a signal without undergoing absorption in the doping region. Thus, a decrease in sensitivity is suppressed. In particular, according to the inventor's findings, if the width of the gap is greater than the thickness of the second semiconductor layer, the decrease in sensitivity can be suppressed even more effectively.

[0008] The semiconductor photodetector according to this disclosure may also be [2] "the semiconductor photodetector according to [1] above, wherein the plurality of portions of the doping region include at least one pair of extending portions that extend in the same direction when viewed from the first direction, and the width of the gap is the distance between the pair of extending portions." According to the semiconductor photodetector according to [2], a structure capable of suppressing a decrease in sensitivity can be easily and reliably constructed.

[0009] The semiconductor photodetector according to this disclosure may also be [3] "the semiconductor photodetector according to [1] or [2] above, wherein the doping region extends from the second semiconductor layer toward the first semiconductor layer and reaches the interior of the first semiconductor layer." According to the semiconductor photodetector according to [3], the doping region may be configured in this manner.

[0010] The semiconductor photodetector relating to this disclosure may also be [4] "a semiconductor photodetector according to any of [1] to [3] above, wherein a recess is formed on the surface, and a light-receiving portion is formed in a region that overlaps with the bottom surface of the recess when viewed from a first direction." According to the semiconductor photodetector relating to [4], the region corresponding to the bottom surface of the recess is used as the light-receiving portion. This protects the light-receiving portion from contact and makes it less susceptible to damage.

[0011] The semiconductor photodetector relating to this disclosure may also be [5] "the semiconductor photodetector according to [4] above, wherein the doping region is exposed on the side surface of the recess." According to the semiconductor photodetector relating to [5], it is possible to extract as a signal light light incident on the gap between the portion of the doping region exposed on the side surface of the recess and the portion opposite to that portion. As a result, a decrease in sensitivity can be suppressed more reliably. In this case, the doping region includes a portion formed from the side surface of the recess to the top surface of the recess (the region defining the recess on the surface). This portion is thicker and has a higher impurity concentration on the surface side compared to the portion formed on the bottom side of the recess in the doping region. Therefore, it is possible to reduce the contact resistance by making contact with the electrode in this portion.

[0012] The semiconductor photodetector according to this disclosure may also be [6] "a semiconductor photodetector according to any one of [1] to [5] above, comprising a third semiconductor layer of the first conductivity type laminated on the second semiconductor layer on the surface side of the second semiconductor layer." According to the semiconductor photodetector according to [6], by using a material with a larger bandgap energy than the first and third semiconductor layers as the second semiconductor layer, it is possible to further reduce losses by reducing dark current and absorption.

[0013] The semiconductor photodetector according to this disclosure may also be [7] "the semiconductor photodetector according to [6] above, comprising a fourth semiconductor layer of the first conductivity type laminated on the third semiconductor layer on the surface side of the third semiconductor layer." According to the semiconductor photodetector according to [7], since the fourth semiconductor layer has the function of protecting the third semiconductor layer, it becomes possible to select a material for the third semiconductor layer that includes a relatively easily oxidized material such as aluminum, thereby improving the freedom of material selection for the third semiconductor layer.

[0014] The semiconductor photodetector relating to this disclosure may also be [8] "a semiconductor photodetector according to any of [1] to [7] above, wherein the first semiconductor layer comprises InGaAs and the second semiconductor layer comprises InP or InAsP."

[0015] The semiconductor photodetector relating to this disclosure may also be [9] "the semiconductor photodetector according to [6] or [7] above, wherein the first semiconductor layer comprises InAsSb or InAs, the second semiconductor layer comprises AlInAsSb, and the third semiconductor layer comprises InAsSb or InPSb."

[0016] The semiconductor photodetector relating to this disclosure may be

[10] "the semiconductor photodetector according to [7] above, wherein the first semiconductor layer comprises InGaAs, the second semiconductor layer comprises InP or InAsP, the third semiconductor layer comprises InGaAs, and the fourth semiconductor layer comprises InP or InAsP." [Effects of the Invention]

[0017] According to this disclosure, it is possible to provide a semiconductor photodetector that can suppress a decrease in sensitivity. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic diagram showing a semiconductor photodetector according to this embodiment. [Figure 2]FIG. 2 is a diagram showing the operation of the semiconductor light receiving element shown in FIG. 1. [Figure 3] FIG. 3 is a diagram showing a step of a method for manufacturing a semiconductor light receiving element. [Figure 4] FIG. 4 is a diagram showing a step of a method for manufacturing a semiconductor light receiving element. [Figure 5] FIG. 5 is a diagram showing a step of a method for manufacturing a semiconductor light receiving element. [Figure 6] FIG. 6 is a schematic cross-sectional view of a semiconductor light receiving element according to a modified example. [Figure 7] FIG. 7 is a schematic plan view of a semiconductor light receiving element according to a modified example. [Figure 8] FIG. 8 is a schematic plan view of a semiconductor light receiving element according to a modified example.

MODE FOR CARRYING OUT THE INVENTION

[0019] Hereinafter, a semiconductor light receiving element according to an embodiment will be described with reference to the drawings. In the description of each figure, elements that are the same or equivalent to each other may be denoted by the same reference numerals, and redundant descriptions may be omitted. In addition, each figure may illustrate an orthogonal coordinate system defined by the X-axis, the Y-axis, and the Z-axis.

[0020] FIG. 1 is a schematic diagram showing the semiconductor light receiving element according to the present embodiment. (a) of FIG. 1 is a plan view, and (b) of FIG. 1 is a cross-sectional view taken along line Ib-Ib of FIG. 1. As shown in FIG. 1, the semiconductor light receiving element 1 includes a first semiconductor portion 10, a second semiconductor portion 20, electrodes 41 and 42, and a protective film F. The semiconductor light receiving element 1 has a front surface 1a and a back surface 1b on the side opposite to the front surface 1a. In the semiconductor light receiving element 1, for example, the front surface 1a is used as a light incident surface. The first semiconductor portion 10 includes the back surface 1b, and the second semiconductor portion 20 includes the front surface 1a. That is, the second semiconductor portion 20 is laminated on the first semiconductor portion 10 on the front surface 1a side.

[0021] The first semiconductor section 10 includes a plurality of semiconductor layers stacked along a first direction (in this case, the Z-axis direction) intersecting the surface 1a. The plurality of semiconductor layers include, for example, a substrate (not shown), a buffer layer (not shown), and a light-absorbing layer (first semiconductor layer) 21 stacked in order from the back surface 1b side.

[0022] The substrate is, for example, a first conductivity type (e.g., n + It consists of InP of type (e.g., n). The buffer layer is, for example, a first conductivity type (e.g., n + It consists of InP of type 1 or type n. For example, the buffer layer has a thickness of about 0.5 μm to 2.0 μm in the first direction. The light absorption layer 21 contains, for example, first conductivity type InGaAs (consisting of InGaAs). For example, the light absorption layer 21 has a thickness of about 1.5 μm to 5 μm in the first direction.

[0023] The second semiconductor section 20 includes a first cap layer (second semiconductor layer) 22, a semiconductor layer (third semiconductor layer) 23, and a second cap layer (fourth semiconductor layer) 24, which are stacked in order from the first semiconductor section 10 side along the first direction. The first cap layer 22 is stacked on the light absorption layer 21 on the surface 1a side of the light absorption layer 21 and has an interface with the light absorption layer 21. The semiconductor layer 23 is stacked on the first cap layer 22 on the surface 1a side of the first cap layer 22 and has an interface with the first cap layer 22. The second cap layer 24 is stacked on the semiconductor layer 23 on the surface 1a side of the semiconductor layer 23 and has an interface with the semiconductor layer 23.

[0024] The first capping layer 22 has a bandgap energy greater than that of the light-absorbing layer 21 and the semiconductor layer 23. The first capping layer 22 contains, for example, InP of a first conductivity type (e.g., n-type). As an example, the first capping layer 22 has a thickness T22 of about 0.1 μm in the first direction. The thickness T22 of the first capping layer 22 in the first direction is thinner than the thickness of the light-absorbing layer 21 in the first direction. The semiconductor layer 23 contains, for example, InGaAs of a first conductivity type (e.g., n-type). As an example, the semiconductor layer 23 has a thickness of about 0.05 μm to 0.3 μm in the first direction. The second capping layer 24 contains, for example, InP of a first conductivity type (e.g., n-type). As an example, the second capping layer 24 has a thickness of about 0.2 μm to 2.0 μm in the first direction.

[0025] Here, a recess 50 is formed on the surface 1a. For example, the surface 1a is circular when viewed from a first direction (i.e., the outer shape of the semiconductor photodetector 1 is circular), and the recess 50 is circular and concentric with the surface 1a when viewed from the first direction. The recess 50 includes a bottom surface 50i and a side surface 50s connecting the bottom surface 50i and the surface 1a. The recess 50 penetrates the second cap layer 24 and the semiconductor layer 23. Therefore, the first cap layer 22 is exposed on the bottom surface 50i of the recess 50 (i.e., the surface of the first cap layer 22 constitutes the bottom surface 50i).

[0026] In other words, the first semiconductor portion 10 and the second semiconductor portion 20 include a first region A that overlaps the bottom surface 50i of the recess 50 when viewed from a first direction, and a second region B outside the first region A, and the semiconductor layer 23 and the second cap layer 24 are formed only in the second region B outside the recess 50. In the semiconductor photodetector 1, the first region A that overlaps the bottom surface 50i of the recess 50 when viewed from a first direction is mainly configured to be relatively thin and is a photodetector 55 that receives incident light and generates an electrical signal.

[0027] The protective film F is provided so as to cover the surface 1a, the side surface 50s of the recess 50, and the bottom surface 50i of the recess 50. The protective film F may also function as an anti-reflective film. Through holes Fh are formed in the protective film F on the second region B, and the second cap layer 24 is exposed through these through holes Fh. The electrode 41 is formed on the back surface 1b and is in contact with the first semiconductor portion 10 (e.g., substrate). The electrode 42 is formed on the protective film F and is in contact with the second cap layer 24 via the through holes Fh.

[0028] The semiconductor photodetector 1 includes a doping region 30. The doping region 30 is a region of second conductivity type (e.g., p-type) by doping the second semiconductor portion 20 and the first semiconductor portion 10 with an impurity (e.g., Zn). The doping region 30 may be a diffusion region formed by doping impurities from the surface 1a side by thermal diffusion. Alternatively, the doping region 30 may be formed by doping impurities by ion implantation. The doping region 30 is formed to extend from the surface 1a toward the first cap layer 22 and reach at least the interior of the first cap layer 22. Here, the doping region 30 extends from the first cap layer 22 toward the light absorption layer 21 and reaches the interior of the light absorption layer 21.

[0029] More specifically, the doping region 30 is formed in the first region A on the first cap layer 22 and a portion of the light absorption layer 21 on the first cap layer 22 side, and in the second region B on the second cap layer 24, semiconductor layer 23, first cap layer 22, and a portion of the light absorption layer 21 on the first cap layer 22 side. The through-holes Fh of the protective film F are formed on the doping region 30, and the electrode 42 is in contact with the doping region 30 at the second cap layer 24 (electrically connected to the doping region 30).

[0030] The doping region 30 includes a plurality of portions 31 that face each other when viewed from a first direction. A gap 30g is interposed between the opposing portions 31. The width G30 of the gap 30g is greater than the thickness T22 of the first cap layer 22. The plurality of portions 31 include a group (at least one pair) of first extending portions 31a that extend in the same direction from each other, and another group (at least one pair) of second extending portions 31b that extend in the same direction but in a different direction from the first extending portions 31a. Here, the first extending portions 31a extend along the X-axis direction, and the second extending portions 31b extend along the Y-axis direction.

[0031] The gap 30g is the gap between adjacent first extending portions 31a and the gap between adjacent second extending portions 31b. Here, the width of the gap between the first extending portions 31a and the width of the gap between the second extending portions 31b are approximately the same, but if they are different, the smaller of the two can be used as the width G30 and may be greater than the thickness T22 of the first cap layer 22. Furthermore, if the width G30 changes along the extending direction of the first extending portion 31a or the second extending portion 31b, its minimum or average value may be greater than the thickness T22.

[0032] The first extending portion 31a and the second extending portion 31b are arranged in a grid pattern by intersecting each other. The first extending portion 31a and the second extending portion 31b are connected to and integrated with the outer edge 32 of the doping region 30 at both ends in their respective extending directions. Here, the electrode 42 is provided in contact with the outer edge 32, so that each of the first extending portion 31a and the second extending portion 31b is also electrically connected to the electrode 42.

[0033] The outer edge 32 is formed straddling the boundary between the first region A and the second region B. That is, the outer edge 32 includes a relatively thick portion located outside the recess 50 and a relatively thin portion located inside the recess 50. As a result, the outer edge 32 is exposed to the side surface 50s of the recess 50 (constituting the side surface 50s). In other words, the doping region 30 is exposed to the side surface 50s of the recess 50.

[0034] Thus, in the semiconductor photodetector 1, the doping region 30 includes a plurality of second conductivity type portions 31 that face each other with a gap 30g between them when viewed from a first direction. As a result, a photodiode (PD) is formed between each of the plurality of portions 31 and the first conductivity type semiconductor region (mainly the light absorption layer 21 and the first cap layer 22) adjacent to each of the plurality of portions 31. Therefore, in the semiconductor photodetector 1, a PD is formed in the first direction for each of the plurality of portions 31, and a plurality of PDs are also formed and dispersed in a plane intersecting the first direction.

[0035] In the semiconductor photodetector 1 described above, as shown in Figure 2, when a voltage is applied to electrodes 41 and 42, an electric field EF is formed within the first semiconductor portion 10 and the second semiconductor portion 20. In this state, if a certain light L1 is incident on and absorbed by one portion 31 of the doping region 30, the light L1 cannot be extracted as a signal because there is no electric field in the doping region 30. On the other hand, if another light L2 is absorbed by the light absorption layer 21 without being absorbed by the doping region 30, it can be extracted as a signal because there is an electric field.

[0036] Furthermore, if another light L3 is incident between portions 31 of the doping region 30 (for example, in the gap 30g) and is absorbed by the first cap layer 22, it is absorbed in the PD formed in a plane intersecting the portion 31 and the first cap layer 22 in the first direction and extracted as a signal. Also, if the light L3 is incident between portions 31 of the doping region 30 and is absorbed by the light absorption layer 21, it is absorbed in the PD formed in the first direction by the portion 31 and the light absorption layer 21 and extracted as a signal. In this way, the semiconductor photodetector 1 makes it possible to extract as a signal even light absorbed by the first cap layer 22, which was not previously extracted as a signal.

[0037] Next, the method for manufacturing the semiconductor photodetector 1 will be described. Figures 3 to 5 show one step in the manufacturing method of the semiconductor photodetector. In this manufacturing method, as shown in Figure 3(a), first, doping regions 30 are formed in the first semiconductor portion 10 and the second semiconductor portion 20. When the doping regions 30 are formed by thermal diffusion, first, a first mask having openings corresponding to the pattern of the doping regions 30 is formed on the surface 1a of the second semiconductor portion 20, and then impurity doping is performed to form the doping regions 30 in the first semiconductor portion 10 and the second semiconductor portion 20. After that, the first mask is removed.

[0038] Next, as shown in Figure 3(b), a second mask M for etching is formed on the surface 1a. Subsequently, as shown in Figure 4(a), recesses 50 are formed on the surface 1a by etching using the second mask M. More specifically, first, the second cap layer 24 is selectively etched and removed using the second mask M. Subsequently, the semiconductor layer 23 is selectively etched and removed using the second mask M.

[0039] As a result, recesses 50 are formed so that the first cap layer 22 is exposed in the region exposed from the second mask M, and a relatively thin portion 31 of the doping region 30 is formed. In addition, in the region covered by the second mask M, the semiconductor layer 23, the second cap layer 24, and a portion of the relatively thick outer edge 32 of the doping region 30 are left intact. In this way, the semiconductor layer 23, as a cap layer on the light absorption layer 21, is selectively etched so that only the thin first cap layer 22 remains in the recesses 50. Subsequently, the second mask M is removed as shown in Figure 4(b).

[0040] Next, as shown in Figure 5(a), a protective film F is formed to cover the surface 1a, the side surface 50s of the recess 50, and the bottom surface 50i of the recess 50. Then, as shown in Figure 5(b), through holes Fh are formed in the protective film F, and electrodes 42 are provided so as to contact the doping region 30 through these through holes Fh. At the same time, electrodes 41 are provided on the back surface 1b. This gives rise to the semiconductor photodetector 1.

[0041] As described above, in the semiconductor photodetector 1, a first cap layer 22 of the first conductivity type with a large bandgap energy is laminated on a first conductivity type light absorption layer 21, and a doping region 30 of the second conductivity type is formed on the side of the first cap layer 22 from the surface 1a that receives incident light. The doping region 30 includes a plurality of portions 31 that face each other across a gap 30g when viewed from a first direction intersecting the surface 1a. Therefore, light incident on the gap 30g of the doping region 30 can be extracted as a signal without undergoing absorption in the doping region 30. Thus, a decrease in sensitivity is suppressed. In particular, according to the inventor's findings, if the width of the gap 30g is greater than the thickness T22 of the first cap layer 22, the decrease in sensitivity can be suppressed even more effectively.

[0042] Furthermore, in the semiconductor photodetector 1, the multiple portions 31 of the doping region 30 include at least one pair of first extending portions 31a (and second extending portions 31b (hereinafter the same)) that extend in the same direction when viewed from the first direction, and the width of the gap 30g is the distance between the pair of first extending portions 31a. This makes it possible to easily and reliably construct a structure that can suppress a decrease in sensitivity.

[0043] Furthermore, in the semiconductor photodetector 1, the doping region 30 extends from the first cap layer 22 towards the light absorption layer 21 and reaches the interior of the light absorption layer 21. The semiconductor photodetector 1 may also have the doping region 30 configured in this way.

[0044] Furthermore, in the semiconductor photodetector 1, a recess 50 is formed on the surface 1a, and a light-receiving portion 55 is formed in the region that overlaps with the bottom surface 50i of the recess 50 when viewed from the first direction. This protects the light-receiving portion 55 from contact and makes it less susceptible to damage.

[0045] Furthermore, in the semiconductor photodetector 1, the doping region 30 is exposed on the side surface 50s of the recess 50. Therefore, light incident on the gap between the portion of the doping region 30 exposed on the side surface 50s of the recess 50 (in this case, the outer edge 32) and the portion 31 opposite to that portion can also be extracted as a signal. As a result, the decrease in sensitivity can be suppressed more reliably. In addition, the doping region 30 includes a portion formed from the side surface 50s of the recess 50 to the top surface of the recess 50 (the region defining the recess 50 on the surface 1a) (the relatively thick portion of the outer edge 32). This portion is thicker and has a higher impurity concentration on the surface 1a side compared to the portion 31 formed on the bottom surface 50i side of the recess 50 in the doping region 30. Therefore, contact resistance can be reduced by making contact with the electrode 42 in this portion.

[0046] Furthermore, the semiconductor photodetector 1 includes a first conductivity type semiconductor layer 23 laminated on the surface 1a side of the first cap layer 22. Therefore, by using a material with a larger bandgap energy than the light absorption layer 21 and the semiconductor layer 23 as the first cap layer 22, it is possible to further reduce losses by reducing dark current and absorption.

[0047] Furthermore, the semiconductor photodetector 1 includes a second cap layer 24 of a first conductivity type laminated on the semiconductor layer 23 on the surface 1a side of the semiconductor layer 23. As a result, since the second cap layer 24 has the function of protecting the semiconductor layer 23, it becomes possible to select a material for the semiconductor layer 23 that includes a relatively easily oxidized material such as aluminum, thereby improving the freedom of material selection for the semiconductor layer 23.

[0048] The embodiments described above illustrate one aspect of the present disclosure. Therefore, the semiconductor photodetector according to the present disclosure may be any modification of the semiconductor photodetector 1 described above. Modifications will be described next. [First variation]

[0049] Figure 6(a) is a schematic cross-sectional view showing a semiconductor photodetector 1A according to the first modified example. The semiconductor photodetector 1A shown in Figure 6(a) differs from the semiconductor photodetector 1 in that it includes a second semiconductor section 20A instead of the second semiconductor section 20. The second semiconductor section 20A differs from the second semiconductor section 20 in that it includes only a single cap layer (second semiconductor layer) 25.

[0050] The cap layer 25 is laminated on the light absorption layer 21 on the surface 1a side of the light absorption layer 21 and has an interface with the light absorption layer 21. The cap layer 25 contains (consists of) InP of a first conductivity type (e.g., n-type). In the semiconductor photodetector 1A as well, the doping region 30 is formed to extend from the surface 1a toward the cap layer 25 and reach at least into the interior of the cap layer 25. More specifically, the doping region 30 extends from the cap layer 25 toward the light absorption layer 21 and reaches into the interior of the light absorption layer 21. Thus, the semiconductor photodetector 1A does not need to have a semiconductor layer 23 and a second cap layer 24 on the light absorption layer 21. Such a semiconductor photodetector 1A can achieve the same effects as the semiconductor photodetector 1, while simplifying the semiconductor laminated structure on the light absorption layer 21. Furthermore, with the semiconductor photodetector 1A, etching becomes possible even for materials that are difficult to selectively etch by time control, enabling thin-film formation regardless of the material. In this case, the width G30 of the gap 30g can be made larger than the thickness of the relatively thin portion of the cap layer 25 located within the recess 50. [Second variation]

[0051] Figure 6(b) is a schematic cross-sectional view showing a semiconductor photodetector 1B according to a second modified example. The semiconductor photodetector 1B shown in Figure 6(b) differs from the semiconductor photodetector 1 in that it includes a second semiconductor section 20B instead of the second semiconductor section 20, and in the materials of each layer. The second semiconductor section 20B differs from the second semiconductor section 20 in that it has a single cap layer (second semiconductor layer) 26 instead of the first cap layer 22, and a semiconductor layer (third semiconductor layer) 27 instead of the semiconductor layer 23.

[0052] In the semiconductor photodetector 1B, the material of the first semiconductor part 10 includes InAsSb. More specifically, in the semiconductor photodetector 1B, at least the light absorption layer 21 is a first conductivity type (e.g., n-type and n-type). + The cap layer 26 contains (or is made of) AlInAsSb of the first conductivity type (e.g., n-type). The cap layer 26 is laminated on the light absorption layer 21 on the surface 1a side and has an interface with the light absorption layer 21. The cap layer 26 contains (or is made of) AlInAsSb of the first conductivity type (e.g., n-type). The semiconductor layer 27 also contains (or is made of) AlInAsSb of the first conductivity type (e.g., n-type).

[0053] In the semiconductor photodetector 1B, the doping region 30 is formed to extend from the surface 1a toward the cap layer 26 and reach at least the interior of the cap layer 26. More specifically, the doping region 30 extends from the cap layer 26 toward the light absorption layer 21 and reaches the interior of the light absorption layer 21. Thus, the semiconductor photodetector 1B does not need to have a second cap layer 24 on the light absorption layer 21. In this case, the same effects as the semiconductor photodetector 1 are achieved, and the semiconductor stacked structure on the light absorption layer 21 is simplified. With such a semiconductor photodetector 1B, the same effects as the semiconductor photodetector 1 are achieved, and the semiconductor stacked structure on the light absorption layer 21 is simplified. Furthermore, with the semiconductor photodetector 1B, if a material that is selectively etchable and has a wide band gap is available, the cap layer itself can be eliminated. This makes it possible to reduce losses in the light-receiving portion, and the contact resistance of the contact portion of the cap layer can be reduced by using a material with a narrow band gap. [Third variation]

[0054] Figure 7(a) is a schematic plan view showing a semiconductor photodetector 1C according to the third modified example. The semiconductor photodetector 1C shown in Figure 7(a) differs from the semiconductor photodetector 1 in the shape of the doping region 30 when viewed from the first direction.

[0055] In the semiconductor photodetector 1C, multiple portions 31 of the doping region 30 include a third extending portion 31c that extends in an annular shape when viewed from a first direction. The third extending portion 31c exhibits an annular shape concentric with the outer edge portion 32 when viewed from a first direction. Therefore, the third extending portion 31c and the outer edge portion 32 constitute a pair of extending portions that extend along the same direction (circumferential direction). Consequently, a gap 30g is formed between the third extending portion 31c and the outer edge portion 32, and at least the width G30 (radial dimension) of this gap 30g is greater than the thickness T22 of the first cap layer 22.

[0056] Furthermore, in the semiconductor photodetector 1C, multiple portions 31 of the doping region 30 are directed in the first direction. Intersecting directions It includes a fourth extending portion 31d extending along the X-axis direction and a fifth extending portion 31e extending along another direction intersecting the first direction (in this case, the Y-axis direction). The fourth extending portion 31d and the fifth extending portion 31e intersect each other. The intersection of the fourth extending portion 31d and the fifth extending portion 31e here substantially coincides with the center of the third extending portion 31c and the outer edge portion 32. The fourth extending portion 31d and the fifth extending portion 31e are connected to the outer edge portion 32 at both ends in their respective extending directions. The third extending portion 31c is also connected to the outer edge portion 32 by being connected to the fourth extending portion 31d and the fifth extending portion 31e.

[0057] The gap between the fourth extending portion 31d and the fifth extending portion 31e, that is, the width of the region enclosed by the fourth extending portion 31d, the fifth extending portion 31e, and the third extending portion 31c, differs at each position in the plane intersecting the first direction, but as an example, its average value may be greater than the thickness T22. Such a semiconductor photodetector 1C can also produce the same effects as the semiconductor photodetector 1. Furthermore, with the semiconductor photodetector 1C, it is possible to easily design a gap (gap 30g) even in a circular shape, and it is also possible to design a combination that maximizes the relationship between the doping region 30 and the gap. [Fourth variation]

[0058] Figure 7(b) is a schematic plan view showing a semiconductor photodetector 1D according to the fourth modified example. The semiconductor photodetector 1D shown in Figure 7(b) differs from the semiconductor photodetector 1 in that it has a rectangular outer shape when viewed from the first direction, and in the shape of the doping region 30 when viewed from the first direction.

[0059] In the semiconductor photodetector 1D, multiple portions 31 of the doping region 30 include a pair of sixth extending portions 31f extending along a direction (in this case, the Y-axis direction) that intersects the first direction. The sixth extending portions 31f extend along the same direction as each other. Therefore, a gap 30g is formed between the sixth extending portions 31f, and at least the width G30 of this gap 30g is greater than the thickness T22 of the first cap layer 22. In addition, in the semiconductor photodetector 1D, a pair of outer edge portions 32 also extend along the same direction as the sixth extending portions 31f. Therefore, the gap between one outer edge portion 32 and the sixth extending portion 31f adjacent to that outer edge portion 32 may be larger than the thickness T22 as the gap 30g.

[0060] Furthermore, in the semiconductor photodetector 1D, the doping region 30 includes a single seventh extending portion 31h that extends along another direction (in this case, the X-axis direction). The seventh extending portion 31h is connected to the outer edge portion 32 at both ends in its extending direction. The sixth extending portion 31f is connected to the seventh extending portion 31h, and thus connected to the outer edge portion 32 via the seventh extending portion 31h. Such a semiconductor photodetector 1D can also achieve the same effects as the semiconductor photodetector 1. Moreover, as shown in Figure 8, the semiconductor photodetector 1D can be easily provided in multiple arrays.

[0061] As shown in Figure 8, when forming a structure in which multiple semiconductor photodetectors 1D are arranged in an array, for example, after forming doping regions 30 at positions corresponding to each semiconductor photodetector 1D as shown in Figure 3, and then forming recesses 50 as shown in Figure 4, etching can be performed integrally across the multiple semiconductor photodetectors 1D (i.e., it is not necessary to place a second mask M between adjacent semiconductor photodetectors 1D). In this case, mutually opposing recesses 50 are integrally formed between adjacent semiconductor photodetectors 1D. Note that in Figure 8, the protective film F is not shown, and the bottom surface 50i of the recess 50 (the surface of the first cap layer 22) is shown.

[0062] On the other hand, when etching to form the recesses 50, a second mask M may be provided between adjacent semiconductor photodetectors 1D to individually form the recesses 50 between multiple semiconductor photodetectors 1D. In this case, between adjacent semiconductor photodetectors 1D, the recesses 50 facing each other will be separated by the surface 1a (a relatively thick portion of the second semiconductor portion 20) that remains unetched between them. [Other variations]

[0063] Although embodiments and several modifications have been described above, the semiconductor photodetectors according to this disclosure are not limited to the semiconductor photodetectors 1 to 1D described above, and further modifications may be applied. For example, in the above embodiments and modifications, the material for the light absorption layer 21 is not limited to InGaAs and InAsSb, but various semiconductors including InAs, GaAs, GaN, InGaN, etc., containing In, P, Al, As, Sb, and Ga can be used.

[0064] Furthermore, the materials for the first cap layer 22, the second cap layer 24, and the cap layers 25 and 26 are not limited to InP and AlInAsSb, but can also be various semiconductors containing In, P, Al, As, Sb, and G, such as InAsP, AlInP, AllnAsP, InPSb, and GaN.

[0065] Furthermore, although the above embodiment described a case in which the doping region 30 extends into the interior of the light-absorbing layer 21, the doping region 30 does not necessarily have to extend into the interior of the light-absorbing layer 21.

[0066] Furthermore, in the semiconductor photodetector 1C according to the third modified example, the doping region 30 may include a plurality of third extending portions 31c having different diameters (concentric), and a gap 30g larger than the thickness T22 may be defined between them. In addition, in the semiconductor photodetector 1C, an undoped region (in other words, a region other than the doping region 30 (hereinafter the same)) may be provided so as to divide the annular third extending portion 31c and the outer edge portion 32 into a plurality of arc-shaped portions. In this case, as an example, the third extending portion 31c and the outer edge portion 32 may be equally divided into four arc-shaped portions by providing one undoped linear region extending on the fourth extending portion 31d and another undoped linear region extending on the fifth extending portion 31e.

[0067] Furthermore, in the semiconductor photodetector 1D according to the fourth modified example, the doping region 30 may include three or more sixth extensions 31f, or the number of sixth extensions 31f may be one. If there is one sixth extension, a gap 30g is formed between the sixth extension 31f and the outer edge 32, and its width should be greater than the thickness T22. Also, in the semiconductor photodetector 1D, the doping region 30 does not have to include the sixth extension 31f. In this case, the gap 30g is defined as the gap between a pair of outer edge portions 32, and its width should be greater than the thickness T22. Moreover, in the semiconductor photodetector 1D, the doping region 30 may include two or more seventh extensions 31h. Note that in the semiconductor photodetector 1D, there may be only one outer edge 32.

[0068] Furthermore, in the semiconductor photodetector 1D, various deformations, including the above deformations, can be arbitrarily combined and applied, and in such cases, the positions of the sixth extension portion 31f and the seventh extension portion 31h can also be arbitrarily set. For example, if the doping region 30 of the semiconductor photodetector 1D does not include the sixth extension portion 31f but includes two seventh extension portions 31h, each of the two seventh extension portions 31h may be arranged to connect the ends of the outer edge portion 32 in the extending direction (here, the Y-axis direction), thereby forming a rectangular annular doping region 30 when viewed from the first direction. Alternatively, if the sixth extension portion 31f is not included but includes one seventh extension portion 31h, the one seventh extension portion 31h may be arranged to connect the centers of the outer edge portion 32 in the extending direction, thereby forming an H-shaped doping region 30 when viewed from the first direction.

[0069] Furthermore, the configurations of the semiconductor photodetectors 1 to 1D can be partially replaced. For example, the doping region 30 pattern of semiconductor photodetectors 1C and 1D may be used as the doping region 30 of semiconductor photodetectors 1A and 1B. [Explanation of Symbols]

[0070] 1,1A,1B,1C,1D… Semiconductor light-receiving element, 1a… Surface, 21… Light-absorbing layer (first semiconductor layer), 22… First cap layer (second semiconductor layer), 23,27… Semiconductor layer (third semiconductor layer), 24… Second cap layer (fourth semiconductor layer), 25,26… Cap layer (second semiconductor layer), 30… Doping area, 30g… Gap, 31… Part, 31a… First extension part (extension part), 31b… Second extension part (extension part), 31c… Third extension part (extension part), 31f… Sixth extension part (extension part), 50… Recess, 50i… Bottom surface, 50s… Side surface, 55… Light-receiving part.

Claims

1. The surface that receives the incident light, A first semiconductor layer of the first conductivity type, A second semiconductor layer of a first conductivity type is laminated on the surface side of the first semiconductor layer and has a bandgap energy larger than the bandgap energy of the first semiconductor layer, A doping region is formed extending from the surface toward the second semiconductor layer and reaching at least into the interior of the second semiconductor layer, and having a second conductivity type different from the first conductivity type, Equipped with, The thickness of the second semiconductor layer in the first direction intersecting the surface is thinner than the thickness of the first semiconductor layer in the first direction. The doping region includes at least one pair of portions that face each other across a gap when viewed from the first direction, The width of the gap is greater than the thickness of the second semiconductor layer in the first direction. The doping region has a connecting portion that connects the pair of parts to each other, and the pair of parts are integrated via the connecting portion. Semiconductor photodetector.

2. The pair of portions of the doping region extend in the same direction when viewed from the first direction. The semiconductor photodetector according to claim 1.

3. The doping region extends from the second semiconductor layer toward the first semiconductor layer and into the interior of the first semiconductor layer. The semiconductor photodetector according to claim 1.

4. The aforementioned surface has a recess formed therein. A light-receiving portion is formed in the region that overlaps with the bottom surface of the recess when viewed from the first direction. The semiconductor photodetector according to claim 1.

5. The doping region is exposed on the side surface of the recess. The semiconductor photodetector according to claim 4.

6. The second semiconductor layer comprises a third semiconductor layer of the first conductivity type laminated on the second semiconductor layer on the surface side of the second semiconductor layer. The semiconductor photodetector according to claim 1.

7. The third semiconductor layer comprises a fourth semiconductor layer of the first conductivity type laminated on the third semiconductor layer on the surface side of the third semiconductor layer, The semiconductor photodetector according to claim 6.

8. The first semiconductor layer comprises InGaAs, The second semiconductor layer includes InP or InAsP. The semiconductor photodetector according to claim 1.

9. The first semiconductor layer comprises InAsSb or InAs. The second semiconductor layer comprises AlInAsSb, The third semiconductor layer includes InAsSb or InPSb. The semiconductor photodetector according to claim 6.

10. The first semiconductor layer comprises InGaAs, The second semiconductor layer comprises InP or InAsP. The third semiconductor layer comprises InGaAs, The fourth semiconductor layer includes InP or InAsP. The semiconductor photodetector according to claim 7.

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