Semiconductor light receiver element

Abstract

A semiconductor light-receiving element comprises: a front surface that receives incident light; a first semiconductor layer of a first conductivity type; a second semiconductor layer of the first conductivity type, stacked on the side of the front surface of the first semiconductor layer and having a bandgap energy greater than the bandgap energy of the first semiconductor layer; and a doped region extending from the front surface toward the second semiconductor layer and reaching at least part of the interior of the second semiconductor layer, and having a second conductivity type different from the first conductivity type. The thickness of the second semiconductor layer in a first direction intersecting the front surface is less than the thickness of the first semiconductor layer in a first direction.The doped region comprises several parts facing each other with a gap between them 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.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a semiconductor light receiving element. STATE OF THE ART

[0002] Patent Literature 1 describes a light-receiving element. This light-receiving element includes a light-absorption layer that absorbs incident light and converts the incident light into an electrical signal, a cover 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 cover layer. The contact layer is made of the same material as the light-absorption layer and is thicker than the cover layer. In addition, in this light-receiving element, a high-concentration impurity region is formed by the P +-Type formed by doping impurities in high concentration near the interface between the light absorption layer and the cover layer and in the cover layer and the contact layer. CITATION LISTPATENT LITERATURE

[0003] Patent Literature 1: Japanese Unexamined Patent Publication No. 2001 - 177142 SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0004] In the light-receiving element described in Patent Literature 1, it can be seen that the high-concentration impurity region is formed over the entire light-receiving surface of the light-absorbing layer and the cover layer. In this case, since light with a wavelength absorbed in the high-concentration impurity region cannot be extracted as a signal, a loss may occur, reducing the sensitivity.

[0005] It is an object of the present disclosure to provide a semiconductor light receiving element capable of suppressing a reduction in sensitivity. SOLUTION TO THE PROBLEM

[0006] A semiconductor light-receiving element according to the present disclosure is [1] “a semiconductor light-receiving element including: a front surface that receives incident light; a first semiconductor layer of a first conductivity type; a second semiconductor layer of the first conductivity type stacked on the first semiconductor layer on the front surface side of the first semiconductor layer and having a band gap energy larger than a band gap energy of the first semiconductor layer;and a doped region formed to extend from the front surface toward the second semiconductor layer side and reach at least the interior of the second semiconductor layer, and having a second conductivity type different from the first conductivity type, wherein a thickness of the second semiconductor layer in a first direction crossing the front surface is smaller than a thickness of the first semiconductor layer in the first direction, the doped region includes a plurality of parts facing each other with a gap therebetween when viewed from the first direction, and a width of the gap is larger than a thickness of the second semiconductor layer in the first direction.";

[0007] In the above semiconductor light-receiving element of [1], a second semiconductor layer of the first conductivity type having a large band gap energy is stacked on a first semiconductor layer of the first conductivity type, and a doped region of the second conductivity type is formed extending from the front surface that receives incident light to the second semiconductor layer side. Then, the doped region includes a plurality of parts facing each other with a gap therebetween when viewed from a first direction crossing the front surface. Therefore, light incident on the gap between the doped regions can be extracted as a signal without being absorbed in the doped regions. Therefore, the reduction in sensitivity is suppressed.In particular, according to the findings of the present inventors, the reduction in sensitivity can be further suppressed when the width of the gap is larger than the thickness of the second semiconductor layer.

[0008] The semiconductor light-receiving element according to the present disclosure may be [2] "the above semiconductor light-receiving element according to [1], wherein the plurality of parts of the doped region include at least a pair of extending portions extending in the same direction when viewed from the first direction, and the width of the gap is a distance between the pair of extending portions." According to the semiconductor light-receiving element described in [2], a structure capable of suppressing a reduction in sensitivity can be formed easily and reliably.

[0009] The semiconductor light-receiving element according to the present disclosure may be [3] "the above semiconductor light-receiving element according to [1] or [2], wherein the doped region extends from the second semiconductor layer to the first semiconductor layer side and reaches the inside of the first semiconductor layer." According to the semiconductor light-receiving element described in [3], the doped region may be formed in this manner.

[0010] The semiconductor light-receiving element according to the present disclosure may be [4] "the semiconductor light-receiving element according to any one of [1] to [3] above, wherein a recess is formed on the front surface, and a light-receiving portion is formed in a region overlapping a bottom surface of the recess when viewed from the first direction." According to the semiconductor light-receiving element described in [4], a region corresponding to the bottom surface of the recess is a light-receiving portion. This protects the light-receiving portion from contact and makes it less susceptible to damage.

[0011] The semiconductor light-receiving element according to the present disclosure may be [5] "the semiconductor light-receiving element according to [4] above, wherein the doped region is exposed on a side surface of the recess." According to the semiconductor light-receiving element described in [5], it is possible to extract as a signal even light incident on the gap between a part of the doped region exposed on the side surface of the recess and a part facing that part. As a result, the decrease in sensitivity can be more reliably suppressed. In addition, in this case, the doped region includes a part formed from the side surface of the recess to the top surface (a region defining the recess on the front surface) of the recess.This part has a portion on the front surface side that is thicker and has a higher impurity concentration than the portion formed on the lower surface side of the recess in the doped region. Therefore, it is possible to reduce the contact resistance by making contact with the electrode at this portion.

[0012] The semiconductor light-receiving element according to the present disclosure may be [6] "the semiconductor light-receiving element according to any one of [1] to [5] above, further including a third semiconductor layer of the first conductivity type stacked on the second semiconductor layer on the front surface side of the second semiconductor layer." According to the semiconductor light-receiving element described in [6], by using a material having a larger band gap energy than the first semiconductor layer and the third semiconductor layer than the second semiconductor layer, it is possible to reduce the dark current and absorption, thereby achieving a further reduction in loss.

[0013] The semiconductor light-receiving element according to the present disclosure may be [7] "the semiconductor light-receiving element according to [6] above, which further includes a fourth semiconductor layer of the first conductivity type stacked on the third semiconductor layer on the front surface side of the third semiconductor layer." According to the semiconductor light-receiving element described in [7], since the fourth semiconductor layer has a function of protecting the third semiconductor layer, a material of the third semiconductor layer containing a relatively easily oxidized material such as aluminum can be selected, thereby improving the freedom in material selection for the third semiconductor layer.

[0014] The semiconductor light receiving element according to the present disclosure may be [8] “the semiconductor light receiving element according to any one of the above [1] to [7], wherein the first semiconductor layer contains InGaAs, and the second semiconductor layer contains InP or InAsP”.

[0015] The semiconductor light-receiving element according to the present disclosure may be [9] “the semiconductor light-receiving element according to [6] or [7] above, wherein the first semiconductor layer contains InAsSb or InAs, the second semiconductor layer contains AlInAsSb, and the third semiconductor layer contains InAsSb or InPSb”.

[0016] The semiconductor light-receiving element according to the present disclosure may be

[10] “the semiconductor light-receiving element according to [7] above, wherein the first semiconductor layer contains InGaAs, the second semiconductor layer contains InP or InAsP, the third semiconductor layer contains InGaAs, and the fourth semiconductor layer contains InP or InAsP”. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0017] According to the present disclosure, it is possible to provide a semiconductor light receiving element capable of suppressing a decrease in sensitivity. SHORT DESCRIPTION OF THE FIGURES [ Fig. 1] Fig. 1 is a schematic drawing showing a semiconductor light receiving element according to the present embodiment. [ Fig. 2] Fig. 2 is a drawing showing the functionality of the Fig. 1 shows the semiconductor light receiving element. [ Fig. 3] Fig. 3 is a drawing showing a step of a method for manufacturing a semiconductor light-receiving element. [ Fig. 4] Fig. 4 is a drawing showing a step of the method for manufacturing a semiconductor light-receiving element. [ Fig. 5] Fig. 5 is a drawing showing a step of the method for manufacturing a semiconductor light-receiving element. [ Fig. 6] Fig. 6 is a schematic sectional view of a semiconductor light receiving element according to a modification example. [ Fig. 7] Fig. 7 is a schematic plan view of a semiconductor light receiving element according to a modification example. [ Fig. 8] Fig. 8 is a schematic plan view of a semiconductor light receiving element according to a modification example. DESCRIPTION OF EMBODIMENTS

[0018] A semiconductor light-receiving element according to an embodiment will be described below with reference to the drawings. In the description of each drawing, like or corresponding elements are denoted by the same reference numerals, and repeated descriptions thereof may be omitted. In addition, each drawing may show a Cartesian coordinate system defined by the X-axis, the Y-axis, and the Z-axis.

[0019] Fig. Fig. 1 is a schematic drawing showing a semiconductor light-receiving element according to the present embodiment. (a) in Fig. 1 is a plan view, and (b) in Fig. 1 is a sectional view along the line Ib-Ib in Fig. 1. As in Fig. As shown in Figure 1, a 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 rear surface 1b opposite the front surface 1a. In the semiconductor light-receiving element 1, for example, the front surface 1a is a light incident surface. The first semiconductor portion 10 includes the rear surface 1b, and the second semiconductor portion 20 includes the front surface 1a. That is, the second semiconductor portion 20 is stacked on the first semiconductor portion 10 on the front surface 1a side.

[0020] The first semiconductor portion 10 includes a plurality of semiconductor layers stacked along a first direction (here, the Z-axis direction) that crosses the front surface 1a. The plurality of semiconductor layers include, for example, a substrate (not shown), a buffer layer (not shown), and a light absorption layer (first semiconductor layer) 21, which are stacked in this order from the rear surface 1b side.

[0021] The substrate is made of InP of a first conductivity type (for example n + -type). The buffer layer is made of InP of the first conductivity type (for example, n +-type or n-type). For example, the buffer layer has a thickness of approximately 0.5 to 2.0 µm in the first direction. The light absorption layer 21 contains, for example, InGaAs (formed from InGaAs) of the first conductivity type. For example, the light absorption layer 21 has a thickness of approximately 1.5 to 5 µm in the first direction.

[0022] The second semiconductor portion 20 includes a first cladding layer (second semiconductor layer) 22, a semiconductor layer (third semiconductor layer) 23, and a second cladding layer (fourth semiconductor layer) 24, which are stacked in this order from the first semiconductor portion 10 side along the first direction. The first cladding layer 22 is stacked on the light absorption layer 21 on the front 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 cladding layer 22 on the front surface 1a side of the first cladding layer 22 and has an interface with the first cladding layer 22. The second cladding layer 24 is stacked on the semiconductor layer 23 on the front surface 1a side of the semiconductor layer 23 and has an interface with the semiconductor layer 23.

[0023] The first cladding layer 22 has a band gap energy that is greater than the band gap energies of the light absorption layer 21 and the semiconductor layer 23. The first cladding layer 22 contains, for example, InP (formed from InP) of the first conductivity type (for example, n-type). For example, the first cladding layer 22 has a thickness T22 of approximately 0.1 µm in the first direction. The thickness T22 of the first cladding layer 22 in the first direction is smaller than the thickness of the light absorption layer 21 in the first direction. The semiconductor layer 23 contains, for example, InGaAs (formed from InGaAs) of the first conductivity type (for example, n-type). For example, the semiconductor layer 23 has a thickness of approximately 0.05 to 0.3 µm in the first direction. The second cover layer 24 contains, for example, InP (is formed from InP) of the first conductivity type (for example, n-type).For example, the second cover layer 24 has a thickness of about 0.2 to 2.0 µm in the first direction.

[0024] Here, a recess 50 is formed on the front surface 1a. For example, the front surface 1a has a circular shape when viewed from the first direction (i.e., the external shape of the semiconductor light-receiving element 1 is circular), and the recess 50 has a circular shape concentric with the front 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 front surface 1a. The recess 50 penetrates the second cladding layer 24 and the semiconductor layer 23. Therefore, the first cladding layer 22 is exposed at the bottom surface 50i of the recess 50 (i.e., the front surface of the first cladding layer 22 forms the bottom surface 50i).

[0025] In other words, the first semiconductor portion 10 and the second semiconductor portion 20 include a first region A that overlaps the lower surface 50i of the recess 50 when viewed from the 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 light-receiving element 1, the first region A that overlaps the lower surface 50i of the recess 50 when viewed from the first direction is formed relatively thin and serves as a light-receiving portion 55 that receives incident light and generates an electrical signal.

[0026] The protective film F is provided to cover the front surface 1a, the side surface 50s of the recess 50, and the bottom surface 50i of the recess 50. The protective film F can function as an anti-reflection film. A through-hole Fh is formed in the protective film F at the second region B, and the second cap layer 24 is exposed from the through-hole Fh. The electrode 41 is formed on the rear surface 1b and is in contact with the first semiconductor portion 10 (for example, a substrate). The electrode 42 is formed on the protective film F and is in contact with the second cap layer 24 via the through-hole Fh.

[0027] The semiconductor light-receiving element 1 includes a doped region 30. The doped region 30 is a region of a second conductivity type (for example, p-type) formed by doping the second semiconductor portion 20 and the first semiconductor portion 10 with impurities (for example, Zn). The doped region 30 may be, for example, a diffusion region formed by doping impurities from the front surface 1a side through thermal diffusion. Alternatively, the doped region 30 may be formed by doping impurities using an ion implantation method. The doped region 30 is formed to extend from the front surface 1a toward the first cladding layer 22 side and to reach at least the interior of the first cladding layer 22.Here, the doped region 30 extends from the first cover layer 22 toward the side of the light absorption layer 21 and reaches the interior of the light absorption layer 21.

[0028] Specifically, in the first region A, the doped region 30 is formed in the first cladding layer 22 and a part of the light absorption layer 21 on the first cladding layer 22 side, and in the second region B, the doped region 30 is formed in the second cladding layer 24, the semiconductor layer 23, the first cladding layer 22, and a part of the light absorption layer 21 on the first cladding layer 22 side. The through-hole Fh of the protective film F is formed at the doped region 30, and the electrode 42 is in contact with the doped region 30 in the second cladding layer 24 (is electrically connected to the doped region 30).

[0029] The doped region 30 includes a plurality of parts 31 facing each other when viewed from the first direction. A gap 30g is arranged between the facing parts 31. The width G30 of the gap 30g is greater than the thickness T22 of the first cladding layer 22. The plurality of parts 31 includes a group (at least a pair) of first extending portions 31a extending in the same direction and another group (at least a pair) of second extending portions 31b extending in the same direction but in a different direction than the first extending portions 31a. Here, the first extending portion 31a extends along the X-axis direction, and the second extending portion 31b extends along the Y-axis direction.

[0030] The gap 30g is a gap between the first extending portions 31a, which are adjacent to each other, and a gap between the second extending portions 31b, which are adjacent to each other. In the present embodiment, 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. However, if they are different, the smaller one may be set as a width G30 and made larger than the thickness T22 of the first cover layer 22. In addition, if the width G30 changes along the extending direction of the first extending portion 31a or the second extending portion 31b, the minimum value or average value thereof may be made larger than the thickness T22.

[0031] The first extending portions 31a and the second extending portions 31b are arranged in a lattice-like structure / pattern by crossing each other. The first extending portion 31a and the second extending portion 31b are integrated by being connected at their two ends in the extending direction to the outer edge portion 32 of the doped region 30. Here, the electrode 42 is provided in contact with the outer edge portion 32, so that the first extending portion 31a and the second extending portion 31b are also electrically connected to the electrode 42.

[0032] The outer edge portion 32 is formed across the boundary between the first region A and the second region B. That is, the outer edge portion 32 includes a relatively thick part located outside the recess 50 and a relatively thin part located inside the recess 50. Therefore, the outer edge portion 32 is exposed on the side surface 50s of the recess 50 (forms the side surface 50s). That is, the doped region 30 is exposed on the side surface 50s of the recess 50.

[0033] In this way, in the semiconductor light-receiving element 1, since the doped region 30 has a plurality of second conductivity-type portions 31 facing each other with the gap 30g therebetween when viewed from the first direction, a PD (photodiode) is formed between each of the plurality of portions 31 and a first conductivity-type semiconductor region (mainly the light absorption layer 21 and the first clad layer 22) adjacent to each of the plurality of portions 31. Therefore, in the semiconductor light-receiving element 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 arranged in a distributed manner in a plane crossing the first direction.

[0034] In the semiconductor light receiving element 1 described above, as shown in Fig. As shown in Figure 2, when a voltage is applied to the electrodes 41 and 42, an electric field EF is generated in the first semiconductor portion 10 and the second semiconductor portion 20. In this state, when predetermined light L1 is incident on a part 31 of the doped region 30 and absorbed, the light L1 cannot be extracted as a signal because no electric field is applied to the doped region 30. On the other hand, when other light L2 is not absorbed in the doped region 30 but by the light absorption layer 21, the light L2 is extracted as a signal because an electric field is applied.

[0035] Furthermore, when another light L3 is incident between the portions 31 of the doped region 30 (for example, onto the gap 30g) and is absorbed by the first cladding layer 22, the light L3 is absorbed by the PD formed in a plane crossing the first direction through the portions 31 and the first cladding layer 22 and is extracted as a signal. Furthermore, when the light L3 is incident between the portions 31 of the doped region 30 and is absorbed by the light absorption layer 21, the light L3 is absorbed by the PD formed in the first direction through the portions 31 and the light absorption layer 21 and is extracted as a signal. Therefore, in the semiconductor light-receiving element 1 itself, light absorbed by the first cladding layer 22 but not extracted as a signal in the past can be extracted as a signal.

[0036] Next, a method for manufacturing the semiconductor light receiving element 1 will be described. Fig. 3 to 5 are drawings showing a step of the method for manufacturing a semiconductor light-receiving element. In this manufacturing method, as shown in (a) in Fig. 3, the doped region 30 is first formed in the first semiconductor portion 10 and the second semiconductor portion 20. In the formation of the doped region 30 by thermal diffusion, a first mask having an opening corresponding to the structure / pattern of the doped region 30 is first formed on the front surface 1a of the second semiconductor portion 20, and then impurities are doped to form the doped region 30 in the first semiconductor portion 10 and the second semiconductor portion 20. Thereafter, the first mask is removed.

[0037] Then, as in (b) in Fig. 3, a second mask M for etching is formed on the front surface 1a. Then, as shown in (a) in Fig. 4, the recess 50 is formed on the front surface 1a by etching using the second mask M. Specifically, first, the second cap layer 24 is removed by selective etching using the second mask M. Then, the semiconductor layer 23 is removed by selective etching using the second mask M.

[0038] As a result, the recess 50 is formed such that the first capping layer 22 is exposed in a region exposed by the second mask M, and the relatively thin part 31 of the doped region 30 is formed. In addition, the semiconductor layer 23, the second capping layer 24, and a part of the relatively thick outer edge portion 32 of the doped region 30 remain in a region covered by the second mask M. In this way, the semiconductor layer 23 can be selectively etched so that only the thin first capping layer 22 remains in the recess 50 as a capping layer on the light absorption layer 21. Thereafter, as in (b) in Fig. 4 shown, the second mask M removed.

[0039] Then, as in (a) in Fig. 5, the protective film F is formed to cover the front surface 1a, the side surface 50s of the recess 50 and the bottom surface 50i of the recess 50. Thereafter, as shown in (b) in Fig. 5, the through-hole Fh is formed in the protective film F, and the electrode 42 is provided so as to contact the doped region 30 through the through-hole Fh. At the same time, the electrode 41 is provided on the rear surface 1b. As a result, the semiconductor light-receiving element 1 is obtained.

[0040] As described above, in the semiconductor light-receiving element 1, the first cladding layer 22 of the first conductivity type, which has a large band gap energy, is stacked on the light-absorbing layer 21 of the first conductivity type, and the doped region 30 of the second conductivity type is formed on the side of the first cladding layer 22 from the front surface 1a that receives incident light. Then, the doped region 30 includes a plurality of parts 31 facing each other with the gap 30g interposed therebetween when viewed from the first direction crossing the front surface 1a. For this reason, light incident at the gap 30g of the doped region 30 can be extracted as a signal without being absorbed in the doped region 30. Therefore, the decrease in sensitivity is suppressed.In particular, according to the findings of the present inventors, the decrease in sensitivity can be further suppressed when the width of the gap 30g is larger than the thickness T22 of the first cover layer 22.

[0041] Moreover, the plurality of parts 31 of the doped region 30 in the semiconductor light-receiving element 1 include at least a pair of first extending portions 31a (and second extending portions 31b (the same as below)) extending in the same direction as viewed from the first direction, and the width of the gap 30g is a distance between the pair of first extending portions 31a. In this way, it is possible to simply and reliably design a structure capable of suppressing a decrease in sensitivity.

[0042] Furthermore, in the semiconductor light-receiving element 1, the doped region 30 extends from the first cladding layer 22 toward the light-absorbing layer 21 side and reaches the inside of the light-absorbing layer 21. In the semiconductor light-receiving element 1, the doped region 30 can be configured in this way.

[0043] Additionally, in the semiconductor light-receiving element 1, the recess 50 is formed on the front surface 1a, and the light-receiving portion 55 is formed in an area overlapping 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.

[0044] Furthermore, in the semiconductor light-receiving element 1, since the doped region 30 is exposed on the side surface 50s of the recess 50, even light incident on the gap between a part (here, the outer edge portion 32) of the doped region 30 exposed on the side surface 50s of the recess 50 and the part 31 facing the part can be extracted as a signal. As a result, the decrease in sensitivity can be more reliably suppressed. In addition, the doped region 30 includes a part (the above-described relatively thick part of the outer edge portion 32) formed from the side surface 50s of the recess 50 to the top surface (a region defining the recess 50 on the front surface 1a) of the recess 50.This part has a portion on the front surface 1a side that is thicker and has a higher impurity concentration than the portion 31 formed on the lower surface 50i side of the recess 50 in the doped region 30. Therefore, it is possible to reduce the contact resistance by making contact with the electrode 42 at this portion.

[0045] In addition, the semiconductor light-receiving element 1 includes the first conductivity type semiconductor layer 23 laminated / stacked on the first cladding layer 22 on the front surface 1a side of the first cladding layer 22. Therefore, by using a material having a larger band gap energy than the light absorption layer 21 and the semiconductor layer 23 as the first cladding layer 22, it is possible to reduce the dark current and absorption, thereby achieving a further reduction in loss.

[0046] Furthermore, the semiconductor light-receiving element 1 includes the second cap layer 24 of the first conductivity type, which is laminated / stacked on the semiconductor layer 23 on the front surface 1a side of the semiconductor layer 23. Therefore, since the second cap layer 24 has a function of protecting the semiconductor layer 23, it is possible to select a material for the semiconductor layer 23 that includes a material that is relatively easily oxidized, such as aluminum, thereby improving the freedom of material selection for the semiconductor layer 23.

[0047] In the above embodiment, one aspect of the present disclosure has been described. Therefore, the semiconductor light-receiving element according to the present disclosure may be any modified version of the semiconductor light-receiving element 1 described above. Modification examples will be described below. [First variation example]

[0048] (a) in Fig. Fig. 6 is a schematic cross-sectional view showing a semiconductor light-receiving element 1A according to a first modification example. The semiconductor light-receiving element 1A shown in (a) Fig. The semiconductor light-receiving element 1A shown in Figure 6 differs from the semiconductor light-receiving element 1 in that the semiconductor light-receiving element 1A has a second semiconductor portion 20A instead of the second semiconductor portion 20. The second semiconductor portion 20A differs from the second semiconductor portion 20 in that the second semiconductor portion 20A includes only a single cap layer (second semiconductor layer) 25.

[0049] The cap layer 25 is stacked on the light absorption layer 21 on the front surface 1a side of the light absorption layer 21 and has an interface with the light absorption layer 21. The cap layer 25 contains InP (formed of InP) of the first conductivity type (for example, n-type). Also in the semiconductor light-receiving element 1A, the doped region 30 is formed to extend from the front surface 1a toward the cap layer 25 side and reach at least the interior of the cap layer 25. Specifically, the doped region 30 extends from the cap layer 25 toward the light absorption layer 21 side and reaches the interior of the light absorption layer 21. Therefore, the semiconductor light-receiving element 1A does not need to have the semiconductor layer 23 and the second cap layer 24 on the light absorption layer 21.By such a semiconductor light-receiving element 1A, the same effects as those of the semiconductor light-receiving element 1 are also achieved, and the semiconductor layer structure at the light-absorbing layer 21 is simplified. In addition, according to the semiconductor light-receiving element 1A, etching can be performed even for materials that are difficult to selectively etch by performing time-controlled etching or the like. Therefore, it is possible to form thin films regardless of the material. Furthermore, in this case, the width G30 of the gap 30g can be made larger than the thickness of the relatively thin part of the cap layer 25 disposed within the recess 50. [Second variation example]

[0050] (am Fig. Fig. 6 is a schematic cross-sectional view showing a semiconductor light-receiving element 1B according to a second modification example. The semiconductor light-receiving element 1B shown in (b) Fig. The semiconductor light-receiving element 1B shown in FIG. 6 differs from the semiconductor light-receiving element 1 in that the semiconductor light-receiving element 1B has a second semiconductor portion 20B instead of the second semiconductor portion 20 and differs in the materials of each layer. The second semiconductor portion 20B differs from the second semiconductor portion 20 in that the second semiconductor portion 20B has a single cap layer (second semiconductor layer) 26 instead of the first cap layer 22 and has a semiconductor layer (third semiconductor layer) 27 instead of the semiconductor layer 23.

[0051] In the semiconductor light-receiving element 1B, the material of the first semiconductor section 10 contains InAsSb. Specifically, in the semiconductor light-receiving element 1B, at least the light absorption layer 21 contains InAsSb (formed of InAsSb) of the first conductivity type (for example, n-type and n +-type). The cap layer 26 is stacked on the light absorption layer 21 on the front surface 1a side and has an interface with the light absorption layer 21. The cap layer 26 contains AlInAsSb (formed of AlInAsSb) of the first conductivity type (for example, n-type). In addition, the semiconductor layer 27 contains InAsSb (formed of InAsSb) of the first conductivity type (for example, n-type).

[0052] Also, in the semiconductor light-receiving element 1B, the doped region 30 is formed so as to extend from the front surface 1a toward the cap layer 26 side and reach at least the inside of the cap layer 26. Specifically, the doped region 30 extends from the cap layer 26 toward the light-absorption layer 21 side and reaches the inside of the light-absorption layer 21. Therefore, the semiconductor light-receiving element 1B does not need to have the second cap layer 24 on the light-absorption layer 21. In this case, the same effects as those of the semiconductor light-receiving element 1 are achieved, and the semiconductor layer structure on the light-absorption layer 21 is simplified. By such a semiconductor light-receiving element 1B, the same effects as those of the semiconductor light-receiving element 1 are also achieved, and the semiconductor layer structure on the light-absorption layer 21 is simplified.Additionally, according to the semiconductor light-receiving element 1B, it is possible to eliminate the cap layer itself by using a material that can be selectively etched and has a wide band gap. Since it is possible to reduce the loss in the light-receiving portion, it is therefore possible to reduce the contact resistance by using a material with a narrow band gap for the contact portion of the cap layer. [Third variation example]

[0053] (a) in Fig. Fig. 7 is a schematic plan view showing a semiconductor light-receiving element 1C according to a third modification example. The semiconductor light-receiving element 1C shown in (a) Fig. The semiconductor light receiving element 1C shown in Fig. 7 differs from the semiconductor light receiving element 1 in the shape of the doped region 30 when viewed from the first direction.

[0054] In the semiconductor light-receiving element 1C, a plurality of parts 31 of the doped region 30 include a third extending portion 31c extending in an annular shape when viewed from the first direction. The third extending portion 31c has an annular shape concentric with the outer edge portion 32 when viewed from the first direction. Therefore, the third extending portion 31c and the outer edge portion 32 form a pair of extending portions extending along the same direction (circumferential direction). Therefore, the gap 30g is formed between the third extending portion 31c and the outer edge portion 32, and at least the width G30 (dimension in the radial direction) of the gap 30g is greater than the thickness T22 of the first cladding layer 22.

[0055] Additionally, in the semiconductor light-receiving element 1C, a plurality of parts 31 of the doped region 30 include a fourth extending portion 31d extending along one direction (here, the X-axis direction) that crosses the first direction, and a fifth extending portion 31e extending along another direction (here, the Y-axis direction) that crosses the first direction. The fourth extending portion 31d and the fifth extending portion 31e intersect each other. Here, the intersection point between the fourth extending portion 31d and the fifth extending portion 31e corresponds approximately to the midpoint / 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 the extending direction.In addition, the third extending portion 31c is connected to the fourth extending portion 31d and the fifth extending portion 31e, thereby being connected to the outer edge portion 32 via the fourth extending portion 31d and the fifth extending portion 31e.

[0056] The gap between the fourth extending portion 31d and the fifth extending portion 31e, that is, the width of a region surrounded by the fourth extending portion 31d, the fifth extending portion 31e, and the third extending portion 31c, differs at each position in a plane crossing the first direction, but, for example, its average value may be greater than the thickness T22. By such a semiconductor light-receiving element 1C, the same effects as those of the semiconductor light-receiving element 1 are also achieved. Moreover, according to the semiconductor light-receiving element 1C, it is possible to easily form a gap (gap 30g) even in a circular shape, and it is possible to design in such a manner that the ratio between the doped region 30 and the gap can be maximized depending on the combination. [Fourth variation example]

[0057] (am Fig. Fig. 7 is a schematic plan view showing a semiconductor light-receiving element 1D according to a fourth modification example. The semiconductor light-receiving element 1D shown in (b) Fig. The semiconductor light receiving element 1D shown in Fig. 7 differs from the semiconductor light receiving element 1 in that the semiconductor light receiving element 1D has a rectangular outer shape when viewed from the first direction and has the shape of the doped region 30 when viewed from the first direction.

[0058] In the semiconductor light-receiving element 1D, a plurality of parts 31 of the doped region 30 include a pair of sixth extending portions 31f extending along a direction (here, the Y-axis direction) that crosses the first direction. The sixth extending portions 31f extend in the same direction. Therefore, the gap 30g is formed between the sixth extending portions 31f, and at least the width G30 of the gap 30g is made larger than the thickness T22 of the first cladding layer 22. In addition, in the semiconductor light-receiving element 1D, a pair of outer edge portions 32 also extend in the same direction as the sixth extending portion 31f. Therefore, the gap between one outer edge portion 32 and the sixth extending portion 31f adjacent to the one outer edge portion 32 can be set as the gap 30g that is larger than the thickness T22.

[0059] In addition, the doped region 30 in the semiconductor light-receiving element 1D includes a single seventh extending portion 31h extending along a different direction (here, the X-axis direction). The seventh extending portion 31h is connected to the outer edge portion 32 at both ends in the extending direction. The sixth extending portion 31f is connected to the seventh extending portion 31h and thereby connected to the outer edge portion 32 via the seventh extending portion 31h. By such a semiconductor light-receiving element 1D, the same effects as by the semiconductor light-receiving element 1 are also achieved. In addition, in the semiconductor light-receiving element 1D, as shown in Fig. 8, a plurality of semiconductor light receiving elements 1D can be easily arranged in an array.

[0060] As in Fig. 8, when forming a structure in which a plurality of semiconductor light receiving elements 1D are arranged in an array, for example, when forming the recess 50 as shown in Fig. 4, after forming the doped region 30 as shown in Fig. 3, at a position corresponding to each of the semiconductor light-receiving elements 1D, etching can be performed simultaneously over the plurality of semiconductor light-receiving elements 1D (ie, it is not necessary to dispose the second mask M between the semiconductor light-receiving elements 1D that are adjacent to each other). In addition, the mutually facing recesses 50 are integrally formed between the adjacent semiconductor light-receiving elements 1D. In addition, in Fig. 8, the protective film F is not shown and the lower surface 50i of the recess 50 (the front surface of the first cover layer 22) is shown.

[0061] On the other hand, in the etching for forming the recesses 50, the second mask M may be provided between the adjacent semiconductor light-receiving elements 1D, so that the recesses 50 are individually formed between the plurality of semiconductor light-receiving elements 1D. In this case, between the adjacent semiconductor light-receiving elements 1D, the recesses 50 facing each other are spaced apart from each other by the front surface 1a (a relatively thick part of the second semiconductor portion 20) remaining unetched between them. [Further variation examples]

[0062] Although the embodiment and several modification examples have been described above, the semiconductor light-receiving element according to the present disclosure is not limited to the semiconductor light-receiving elements 1 to 1D described above, and further modifications may be applied. For example, in the embodiment and modification examples described above, the material of the light absorption layer 21 is not limited to InGaAs and InAsSb, but various other semiconductors including In, P, Al, As, Sb, and Ga, such as InAs, GaAs, GaN, and InGaN, may be used.

[0063] Furthermore, the materials or 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 various other semiconductors containing In, P, Al, As, Sb and G, such as InAsP, AlInP, AlnAsP, InPSb and GaN, may be used.

[0064] In addition, in the above embodiment, the case where the doped region 30 reaches the inside of the light absorption layer 21 has been described, but the doped region 30 may not reach the inside of the light absorption layer 21.

[0065] Additionally, in the semiconductor light-receiving element 1C according to the third modification example, the doped region 30 may include a plurality of third extending portions 31c having different diameters (concentric third extending portions 31c), and the gap 30g larger than the thickness T22 may be defined between them. Additionally, in the semiconductor light-receiving element 1C, an undoped region (in other words, a region other than the doped region 30 (the same hereinafter)) may be provided to divide the annular third extending portion 31c and the outer edge portion 32 into a plurality of arcuate parts.In this case, for example, the third extending portion 31c and the outer edge portion 32 may be equally divided into four arcuate parts by providing an undoped linear region extending to the fourth extending portion 31d and another undoped linear region extending to the fifth extending portion 31e.

[0066] Additionally, in the semiconductor light-receiving element 1D according to the fourth modification example, the doped region 30 may include three or more sixth extending portions 31f, or the number of the sixth extending portions 31f may be one. When the number of the sixth extending portions 31f is one, the gap 30g may be formed between the sixth extending portion 31f and the outer edge portion 32, and the width of the gap 30g may be made larger than the thickness T22. Additionally, in the semiconductor light-receiving element 1D, the doped region 30 may not include the sixth extending portion 31f. In this case, the gap between a pair of outer edge portions 32 may be defined as the gap 30g, and the width of the gap 30g may be set to be larger than the thickness T22.Additionally, the doped region 30 in the semiconductor light-receiving element 1D may include two or more seventh extending portions 31h. Additionally, only one outer edge portion 32 may be provided in the semiconductor light-receiving element 1D.

[0067] Then, in the semiconductor light-receiving element 1D, various modifications, including those described above, can be applied in any combination, and in this case, the positions of the sixth extending portion 31f and the seventh extending portion 31h can also be arbitrarily determined. For example, when the doped region 30 of the semiconductor light-receiving element 1D does not include the sixth extending portion 31f but has two seventh extending portions 31h, the two seventh extending portions 31h can be arranged so that their ends are connected to each other in the extending direction (here, the Y-axis direction) of the outer edge portion 32, so that the doped region 30 as a whole has a rectangular ring shape when viewed from the first direction.Alternatively, when the sixth extending portion 31f is not included but a seventh extending portion 31h is included, the seventh extending portion 31h may be arranged such that its centers are connected in the extending direction (here, the Y-axis direction) of the outer edge portion 32, so that the doped region 30 as a whole has an H-shape when viewed from the first direction.

[0068] In addition, the configuration of each of the semiconductor light-receiving elements 1 to 1D can be partially substituted for use. For example, the structure / pattern of the doped region 30 in the semiconductor light-receiving elements 1C and 1D can be adopted as the doped region 30 in the semiconductor light-receiving element 1A or the semiconductor light-receiving element 1B. LIST OF REFERENCE SYMBOLS 1, 1A, 1B, 1C, 1D semiconductor light receiving element, 1a front surface 21 Light absorption layer (first semiconductor layer) 22 first cover layer (second semiconductor layer) 23, 27 Semiconductor layer (third semiconductor layer) 24 second top layer (fourth 25, 26 Cover layer (second semiconductor layer) 30 semiconductor layer) doped area 30g gap 31 gap 31a first extending section (extending section), 31b second extending section (extending section) 31c third extending section (extending section) 31f sixth 50 extending section (extending section) 50i recess, lower 55 Surface, side surface, light receiving section. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2001 - 177142

[0003]

Claims

[1] A semiconductor light-receiving element comprising: a front surface that receives incident light; a first semiconductor layer of a first conductivity type; a second semiconductor layer of the first conductivity type stacked on the first semiconductor layer on the front surface side of the first semiconductor layer and having a band gap energy larger than a band gap energy of the first semiconductor layer; and a doped region formed to extend from the front surface toward the side of the second semiconductor layer and to reach at least the interior of the second semiconductor layer, and having a second conductivity type different from the first conductivity type, wherein a thickness of the second semiconductor layer in a first direction crossing the front surface is smaller than a thickness of the first semiconductor layer in the first direction, the doped region comprises a plurality of parts facing each other with a gap therebetween when viewed from the first direction, and a width of the gap is greater than a thickness of the second semiconductor layer in the first direction. [2] A semiconductor light-receiving element according to claim 1, wherein the plurality of parts of the doped region include at least a pair of extending portions extending in the same direction when viewed from the first direction, and the width of the gap is a distance between the pair of extending portions. [3] A semiconductor light receiving element according to claim 1, wherein the doped region extends from the second semiconductor layer toward the first semiconductor layer side and reaches the inside of the first semiconductor layer. [4] A semiconductor light-receiving element according to claim 1, wherein a recess is formed on the front surface, and a light receiving portion is formed in a region overlapping a lower surface of the recess when viewed from the first direction. [5] A semiconductor light receiving element according to claim 4, wherein the doped region is exposed on a side surface of the recess. [6] A semiconductor light-receiving element according to claim 1, further comprising: a third semiconductor layer of the first conductivity type stacked on the second semiconductor layer on the front surface side of the second semiconductor layer. [7] A semiconductor light-receiving element according to claim 6, further comprising: a fourth semiconductor layer of the first conductivity type stacked on the third semiconductor layer on the side of the front surface of the third semiconductor layer. [8] A semiconductor light-receiving element according to claim 1, wherein the first semiconductor layer contains InGaAs, and the second semiconductor layer contains InP or InAsP. [9] A semiconductor light-receiving element according to claim 6, wherein the first semiconductor layer contains InAsSb or InAs, the second semiconductor layer contains AlInAsSb, and the third semiconductor layer contains InAsSb or InPSb. [10] A semiconductor light-receiving element according to claim 7, wherein the first semiconductor layer contains InGaAs, the second semiconductor layer contains InP or InAsP, the third semiconductor layer contains InGaAs, and the fourth semiconductor layer contains InP or InAsP.

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