Semiconductor photodetector

Abstract

To ensure the coverage of an insulating film.SOLUTION: A semiconductor photodetector includes a substrate 10, a mesa structure 14 on the substrate 10, which is composed of multiple layers including an upper layer and a lower layer, in which the upper layer is a light absorbing layer 16, and the lower layer is a wide band gap layer 18 with a band gap wide enough not to absorb light, and an insulating film 26 covering the side surface of the mesa structure 14, and each of the multiple layers is composed of a single crystal of a III-V group semiconductor, the upper surface is the (100) plane, and the upper surface of the wide band gap layer 18 is shaped to include a pair of vertices V in the [0-11] direction and the [01-1] direction on the circumference of the smallest inclusive circle C.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD

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

BACKGROUND ART

[0002] The transmission speed in optical communication is increasing, and high-speed responsiveness of optical modules is required. A semiconductor light-receiving element with excellent high-speed responsiveness includes a frustoconical mesa structure (Patent Document 1). The mesa structure is composed of a plurality of stacked semiconductor layers and is covered with an insulating film (Patent Document 2).

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0003]

PATENT DOCUMENT 1

PATENT DOCUMENT 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] When crystal anisotropic etching is applied in the formation process of the mesa structure, the mesa structure may have an inverted frustoconical shape. In such a case, since the side surface is a reverse tapered surface, the coverage of the insulating film is lowered, which may lead to deterioration in reliability and characteristics.

[0005] The present invention aims to ensure the coverage of the insulating film.

MEANS FOR SOLVING THE PROBLEMS

[0006] The semiconductor photodetector comprises a substrate, a mesa structure on the substrate consisting of multiple layers including an upper layer and a lower layer, the upper layer being a light absorption layer and the lower layer being a wide-bandgap layer with a bandgap wide enough not to absorb light, and an insulating film covering the sides of the mesa structure, each of the multiple layers being made of a single crystal of a III-V semiconductor with the (100) plane as the upper surface, and the upper surface of the wide-bandgap layer having a pair of vertices in the [0-11] direction and the [01-1] direction, with the minimum encapsulation comprising It is a shape that lies within the circumference of a circle. [Brief explanation of the drawing]

[0007] [FIG. 1] This is a plan view of a semiconductor photodetector according to the first embodiment. [FIG. 2] Figure 1 is an enlarged cross-sectional view of the semiconductor photodetector along line II-II. [FIG. 3] Figure 1 is an enlarged cross-sectional view of the semiconductor photodetector along line III-III. [FIG. 4] This is a plan view of a semiconductor photodetector according to a modified example of the first embodiment. [FIG. 5] This is a plan view of a semiconductor photodetector according to the second embodiment. [FIG. 6] Figure 5 is an enlarged cross-sectional view of the semiconductor photodetector along the line VI-VI. [FIG. 7] Figure 5 is an enlarged cross-sectional view of the semiconductor photodetector along line VII-VII. [FIG. 8] This is a plan view of a semiconductor photodetector according to a modified example of the second embodiment. [FIG. 9] This is a plan view of a semiconductor photodetector according to the third embodiment. [FIG. 10] Figure 9 is an enlarged cross-sectional view of the semiconductor photodetector along line XX. [FIG. 11] Figure 9 is an enlarged cross-sectional view of the semiconductor photodetector along the XI-XI line. [FIG. 12] This is a plan view of a semiconductor photodetector according to the fourth embodiment. [FIG. 13] Figure 12 is an enlarged cross-sectional view of the semiconductor photodetector along line XIII-XIII. [FIG. 14] Figure 2 is an enlarged cross-sectional view of the semiconductor photodetector along the XIV-XIV line. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described specifically and in detail below with reference to the drawings. Components denoted by the same reference numerals in all figures have the same or equivalent function, and repeated explanations will be omitted. Note that the size of the figures does not necessarily correspond to the magnification.

[0009] [First Embodiment] Figure 1 is a plan view of a semiconductor photodetector according to the first embodiment. Figure 2 is an enlarged cross-sectional view of the semiconductor photodetector of Figure 1 taken along line II-II. Figure 3 is an enlarged cross-sectional view of the semiconductor photodetector of Figure 1 taken along line III-III.

[0010] Semiconductor photodetectors correspond to wavelength bands used in optical communications and the like. These semiconductor photodetectors are surface-incident semiconductor photodetectors where signal light is incident from the front. For example, they may be PIN-type photodetectors with an intrinsic semiconductor layer inserted between a p-type and an n-type semiconductor layer, but they may also be avalanche photodiodes (APDs).

[0011] [substrate] The semiconductor photodetector has a substrate 10. The substrate 10 is made of a single crystal of a III-V semiconductor (e.g., Fe-doped InP) and has a (100) plane, represented by Miller indices, as its upper surface. A first contact layer 12 is provided on the substrate 10. The first contact layer 12 is a semiconductor layer of a first conductivity type (e.g., n-type).

[0012] [Mesa structure] The semiconductor light-receiving element has a mesa structure 14 on a substrate 10. Signal light is adapted to enter from the top surface of the mesa structure 14. The mesa structure 14 is arranged on the substrate 10 (specifically, on the first contact layer 12). The mesa structure 14 is in contact with and electrically connected to the first contact layer 12.

[0013] The mesa structure 14 is composed of a plurality of layers. Each of the plurality of layers is made of a single crystal of a III-V group semiconductor, with the (100) plane as the top surface. The plurality of layers includes an upper layer and a lower layer. The upper layer is not the uppermost layer, but may be the uppermost layer.

[0014] [Upper layer] The upper layer of the mesa structure 14 is a light absorption layer 16. The absorption layer 16 is made of InGaAs. Light incident on the mesa structure 14 enters the absorption layer 16, is absorbed, and is converted into electricity. The absorption layer 16 is adapted to convert signal light into an electric signal. The absorption layer 16 may be either an intrinsic semiconductor layer or a conductive-type semiconductor layer, or may be a combination of both. The intrinsic semiconductor may be not only a semiconductor having no polarity at all, but also a semiconductor that does not intentionally contain additives for imparting polarity, that is, a semiconductor containing a trace amount of additives at the background level.

[0015] The top surface of the absorption layer 16 has a shape that includes a pair of vertices V in the [0-11] direction and the [01-1] direction (opposite to each other along the first direction D1) on the circumference of the smallest enclosing comprising circle C. The angle of each of the pair of vertices V is 135 degrees or less. The vertex V includes not only a point where the ends of two straight lines meet, but also a point where two curves meet.

[0016] The top surface of the absorption layer 16 has a shape that includes a pair of tips in the

[0011] direction and the [0-1-1] direction (opposite to each other along the second direction D2 orthogonal to the first direction D1) inside the smallest enclosing comprising circle C. The top surface of the absorption layer 16 has a shape including a pair of arcs that are convex in the

[0011] direction and the [0-1-1] direction (the second direction D2), respectively.

[0017] [Lower layer] The layer beneath the mesa structure 14 is a wide-bandgap layer 18, which has a bandgap wide enough not to absorb light. The wide-bandgap layer 18 has a wider bandgap than the absorption layer 16 and does not absorb light that has passed through the absorption layer 16 (i.e., incoming light). The wide-bandgap layer 18 is an intrinsic semiconductor and is composed of one of InAlGaAs, InAlAs, or InP.

[0018] The wide bandgap layer 18 is thicker than the absorption layer 16. When a voltage is applied, the wide bandgap layer 18 and the absorption layer 16 become depleted, forming a depletion layer. The presence of the wide bandgap layer 18 allows for a thicker depletion layer, thereby reducing parasitic capacitance and enabling high-speed operation.

[0019] The upper surface of the wide bandgap layer 18 has a pair of vertices V in the [0-11] direction and the [01-1] direction (first direction D1), which are minimally encapsulated. comprising The shape is contained within the circumference of circle C. The angles of each of the pair of vertices V are 135 degrees or less.

[0020] In the formation process of the mesa structure 14, a semiconductor layer is grown as a crystal and etched through a mask. Since etching is dependent on the crystal orientation, crystal planes appear, and the side surface in the first direction D1 becomes an inverse tapered surface. If the planar shape of the mask is circular, the side surface also becomes an inverse tapered surface in a direction slightly deviated from the first direction D1, and the inverse tapered surface becomes wider.

[0021] In this embodiment, since the planar shape has a vertex V in the first direction D1, even the side surface slightly offset from the first direction D1 becomes a forward tapered surface or a vertical surface. Due to this influence, the side surface in the first direction D1 does not become an inverse tapered surface but is a vertical shape or a forward tapered surface. Even if vertex V is the intersection point of two curves, an inverse tapered surface does not appear because the side surface in the first direction D1 is small.

[0022] The upper surface of the wide bandgap layer 18 has a pair of tips in the

[0011] direction and the [0-1-1] direction (second direction D2), which is minimally encapsulated.comprising This shape is contained within circle C. Since the capacitance of a semiconductor photodetector is proportional to the area of ​​the depleted layer, reducing the area of ​​the mesa structure 14 in a plan view suppresses the increase in parasitic capacitance and enables high-speed operation.

[0023] The upper surface of the wide bandgap layer 18 has a shape that includes a pair of convex arcs in the

[0011] direction and the [0-1-1] direction (second direction D2), respectively. The upper surface of the wide bandgap layer 18 coincides with the lower surface of the absorption layer 16 in terms of its outer shape.

[0024] [Top layer] The uppermost layer of the multi-layer structure is the second contact layer 20, which has a band gap wide enough not to absorb incident light and is a semiconductor layer (e.g., an InGaAs layer) of the second conductivity type (e.g., p-type).

[0025] The upper surface of the second contact layer 20 has a pair of vertices V in the [0-11] direction and the [01-1] direction (first direction D1) that are minimally encapsulated. comprising The shape is contained within the circumference of circle C. The angles of each of the pair of vertices V are 135 degrees or less.

[0026] The upper surface of the second contact layer 20 has a pair of tips in the

[0011] direction and the [0-1-1] direction (second direction D2), which is minimally encapsulated. comprising The shape is contained within circle C. The upper surface of the second contact layer 20 has a shape that includes a pair of convex arcs in the

[0011] direction and the [0-1-1] direction (second direction D2), respectively. The lower surface of the second contact layer 20 coincides with the upper surface of the absorption layer 16 in its outer shape.

[0027] In this embodiment, the multiple layers included in the mesa structure 14 consist only of the minimum necessary elements, but other layers may also be included. For example, the multiple layers may include an etch stop layer between the first contact layer 12 and the wide bandgap layer 18, or an InAlGaAs cap layer between the absorption layer 16 and the second contact layer 20.

[0028] [Convex structure] A first convex structure 22 is provided above the substrate 10. The first convex structure 22 consists of multiple layers and has the same layer structure as the mesa structure 14, except that the bottom layer is the same layer as the first contact layer 12. However, the planar shape is different.

[0029] A second convex structure 24 is provided above the substrate 10. The second convex structure 24 has the same layer structure as the first convex structure 22. The mesa structure 14, the first convex structure 22, and the second convex structure 24 can be formed by growing the above-described layer structures using an MBE (Molecular Beam Epitaxy) apparatus, and then separating them using lithography techniques.

[0030] [Insulated film] The semiconductor photodetector has an insulating film 26 covering the sides of the mesa structure 14. The insulating film 26 covers and protects the mesa structure 14, the first convex structure 22, the second convex structure 24, and the exposed surface (e.g., the entire surface) of the substrate 10. The insulating film 26 is a passivation film, such as an oxide film or a nitride film, for example, a silicon oxide film or a silicon nitride film. The insulating film 26 is formed on a portion of the upper surface of the first contact layer 12, forming a first through-hole 28. The insulating film 26 is not formed on a portion of the upper surface of the mesa structure 14, thereby forming a second through-hole 30.

[0031] The insulating film 26 (passivation film) protects the semiconductor constituting the mesa structure 14 and reduces leakage current. In this embodiment, since the side surface of the mesa structure 14 is not an inverse tapered surface, the insulating film 26 has good coverage, resulting in high reliability and characteristics of the semiconductor photodetector.

[0032] [Electrode Pattern] The semiconductor photodetector has an electrode pattern 32. The electrode pattern 32 includes a first electrode 34. The first electrode 34 is located on one side of the substrate 10. Multiple portions of the first electrode 34 are integral.

[0033] The first electrode 34 includes a mesa electrode 36 located on the upper surface of the mesa structure 14. The outer shape of the upper surface of the mesa electrode 36 is circular, but it may also be shaped to conform to the shape of the mesa structure 14. The mesa electrode 36 and the second contact layer 20 are connected by a second through-hole 30 in the insulating film 26. The mesa electrode 36 is in contact (physically and electrically connected) with the upper surface of the second contact layer 20. The mesa electrode 36 has an aperture 38 in plan view. The aperture 38 is shaped so that signal light can enter it. The aperture 38 is circular. The mesa electrode 36 is ring-shaped in plan view, but it may also be C-shaped with a part that is not connected.

[0034] The first electrode 34 includes a first external electrode 40 (e.g., a pad). The first external electrode 40 is positioned to cover the upper surface of the first convex structure 22 and is bonded to a wire (not shown) to provide an electrical connection with an external device (e.g., a transimpedance amplifier). The first external electrode 40 is located on an insulating film 26.

[0035] The first electrode 34 includes a first connecting electrode 42 that connects the first external electrode 40 and the mesa electrode 36. The width of the first connecting electrode 42 perpendicular to the direction of extension is narrower than the width of either the first external electrode 40 or the mesa electrode 36. The first connecting electrode 42 extends from the mesa electrode 36 in the

[0011] direction or the [0-1-1] direction (second direction D2). Since the side surface of the mesa structure 14 is a forward tapered surface in this direction, the first connecting electrode 42 does not break.

[0036] The electrode pattern 32 includes a second electrode 44. The second electrode 44 is located on one side of the substrate 10. Multiple portions of the second electrode 44 are integral. The second electrode 44 includes a pair of second external electrodes 46. The first external electrode 40 is located between the pair of second external electrodes 46. The second external electrode 46 includes a region (e.g., a pad) located on the upper surface of the second convex structure 24 and a region on the side of the second convex structure 24. The second electrode 44 includes a second connecting electrode 48 that connects the pair of second external electrodes 46. The second connecting electrode 48 contacts the first contact layer 12 inside the first through-hole 28 of the insulating film 26. By applying a voltage between the first electrode 34 and the second electrode 44, light (optical signal) entering the mesa structure 14 is absorbed, and an electrical signal is obtained.

[0037] [Modified version of the first embodiment] Figure 4 is a plan view of a semiconductor photodetector according to a modification of the first embodiment. The upper surface of the wide bandgap layer 18 has a minimum encapsulation of a pair of vertices V' in the

[0011] direction and the [0-1-1] direction (second direction D2). comprising The shape is contained within the circumference of circle C'. The upper surface of the wide bandgap layer 18 is polygonal (for example, a regular octagon).

[0038] Thus, the top surface may be a shape composed solely of straight lines. The angle θ of the vertex V' (the angle between the two straight lines) is preferably 135 degrees or less. If the angle is larger than this, the shape of the top surface will become closer to a circle, and there is a risk of an inverse tapered surface appearing.

[0039] The upper surfaces of the layers above the wide bandgap layer 18 (the uppermost layer and the absorption layer 16) have a pair of vertices V' in the [0-11] direction and the [01-1] direction (first direction D1) that are minimally encapsulated. comprising The shape is contained within the circumference of circle C'. The upper surface of the wide bandgap layer 18 coincides with the lower surface of the absorption layer 16 in terms of its outer shape.

[0040] [Second Embodiment] Figure 5 is a plan view of a semiconductor photodetector according to the second embodiment. Figure 6 is an enlarged cross-sectional view of the semiconductor photodetector of Figure 5 taken along line VI-VI. Figure 7 is an enlarged cross-sectional view of the semiconductor photodetector of Figure 5 taken along line VII-VII.

[0041] The mesa structure 214 has a two-stage structure including an upper mesa structure 250 and a lower mesa structure 252. The upper mesa structure 250 includes an absorption layer 216 and a second contact layer 220. The lower mesa structure 252 includes a wide bandgap layer 218.

[0042] The upper surface of the upper mesa structure 250 is circular. That is, the upper surfaces of the layers above the wide bandgap layer 218 (the uppermost layer and the absorption layer 216) are circular. Therefore, the sides of the upper mesa structure 250 include an inverse tapered surface. The upper surface of the wide bandgap layer 218 protrudes from the absorption layer 216.

[0043] The capacitance of a semiconductor photodetector is proportional to the area of ​​the depleted layer, and the beam shape of the incident light is generally circular. Therefore, in order to ensure light detection efficiency without adding unnecessary capacitance, the area of ​​the depleted layer should be circular. The depleted layers are the absorption layer 216 and the wide bandgap layer 218, which are included in the upper mesa structure 250 and the lower mesa structure 252, respectively.

[0044] However, if the upper surfaces of both the upper mesa structure 250 and the lower mesa structure 252 are made circular, both sides become inversely tapered surfaces, which has a significant impact on the coverage of the insulating film 226. The first embodiment solves this problem, but the upper surface becomes larger than the beam shape of the incident light, which is disadvantageous in terms of capacitance.

[0045] Therefore, in this embodiment, the upper surface of the lower mesa structure 252 has the same shape as the upper surface of the wide bandgap layer 218 in the first embodiment, while the upper surface of the upper mesa structure 250 is circular in order to suppress an increase in capacitance. As a result, an inverse tapered surface appears, but no inverse tapered surface appears on the side surface of the lower mesa structure 252, thereby reducing the possibility of a decrease in the coverage of the insulating film 226.

[0046] The wide bandgap layer 218 is a layer placed to reduce capacitance and tends to be thicker than other layers (e.g., the absorption layer 216). If the sides of the thick layer become inversely tapered, the coverage of the insulating film 226 will decrease significantly, so the upper surface of the lower mesa structure 252, which includes the wide bandgap layer 218, is not circular in shape.

[0047] The thickness of the depletion layer is limited by the concentration of impurities it contains; the lower the impurity concentration, the thicker the depletion layer. In other words, if a certain concentration of impurities is present, the thickness of the depletion layer is effectively limited, no matter how thick the layer itself becomes.

[0048] Since the impurity concentration can be lower with InP than with InAlGaAs, the depletion layer of a layer formed with InP can be effectively thicker than that of a layer formed with InAlGaAs. Therefore, if the wide bandgap layer 218 is formed thicker with InP, the region that is depleted can be widened accordingly. Forming a thick wide bandgap layer 218 widens the inverse tapered surface and reduces the coverage of the insulating film 226, but according to this embodiment, the coverage of the insulating film 226 can also be ensured. The contents described in the first embodiment can be applied to other points.

[0049] [Modified version of the second embodiment] Figure 8 is a plan view of a semiconductor photodetector according to a modified example of the second embodiment. The upper surface of the wide bandgap layer 218 has a minimum encapsulation of a pair of vertices V' in the

[0011] direction and the [0-1-1] direction (second direction D2). comprising The shape is contained within the circumference of circle C'. The upper surface of the wide bandgap layer 218 is polygonal (e.g., rhombus or regular octagon).

[0050] Other aspects are the same as in the second embodiment. The upper surface of the wide bandgap layer 218 has a pair of vertices V' in the [0-11] direction and the [01-1] direction (first direction D1) that are minimally encapsulated. comprisingThe shape is contained within the circumference of circle C'. The upper surfaces of the layers above the wide bandgap layer 218 (the uppermost layer and the absorption layer 216) are circular. The upper surface of the wide bandgap layer 218 protrudes from the absorption layer 216.

[0051] [Third Embodiment] Figure 9 is a plan view of a semiconductor photodetector according to the third embodiment. Figure 10 is an enlarged cross-sectional view of the semiconductor photodetector of Figure 9 along line XX. Figure 11 is an enlarged cross-sectional view of the semiconductor photodetector of Figure 9 along line XI-XI.

[0052] The mesa structure 314 has a two-tiered structure including an upper mesa structure 350 and a lower mesa structure 352. The upper surface of the wide bandgap layer 318 protrudes from the absorption layer 316. The upper surfaces of the upper mesa structure 350 and the lower mesa structure 352 are similar in shape, although they differ in size. Alternatively, the upper surface of the upper mesa structure 350 may be rhomboid and the upper surface of the lower mesa structure 352 may be octagonal, for example, and they may have different shapes.

[0053] The upper surface of the upper mesa structure 350 is not circular, but has a structure with vertices V in the first direction D1. More specifically, the upper surfaces of the layers above the wide bandgap layer 318 (the uppermost layer and the absorption layer 316) have a pair of vertices V1 in the [0-11] direction and the [01-1] direction (first direction D1), and are minimally encapsulated. comprising The shape is included on the circumference of circle C1. Therefore, since the side surface of the upper mesa structure 350 does not include an inverse tapered surface, the coverage of the insulating film 326 is excellent.

[0054] The provisions described in the first embodiment are applicable to other aspects. The upper surface of the wide bandgap layer 318 has a minimum encapsulation of a pair of vertices V2 in the [0-11] direction and the [01-1] direction (first direction D1). comprising This shape lies on the circumference of circle C2.

[0055] [Fourth Embodiment] Figure 12 is a plan view of a semiconductor photodetector according to the fourth embodiment. Figure 13 is an enlarged cross-sectional view of the semiconductor photodetector of Figure 12 taken along line XIII-XIII. Figure 14 is an enlarged cross-sectional view of the semiconductor photodetector of Figure 2 taken along line XIV-XIV.

[0056] The substrate 410 has a shape that allows signal light to be incident from the opposite side of the mesa structure 414. A lens 454 is formed on the back surface of the substrate 410. The lens 454 is designed to focus light incident from the outside. The semiconductor photodetector is a back-incident type semiconductor photodetector in which signal light is incident from the back. The other aspects can be applied as described in the first embodiment.

[0057] A first contact layer 412 is provided on the upper surface of the substrate 410. The first contact layer 412 is a semiconductor layer of first conductivity type (e.g., n-type). The mesa structure 414 is located on the upper surface of the substrate 410 (specifically on top of the first contact layer 412). The mesa structure 414 is in contact with the first contact layer 412 and is electrically connected to it.

[0058] Light entering the mesa structure 414 is incident on the absorption layer 416, absorbed, and converted into electricity. The absorption layer 416 may be an intrinsic semiconductor layer, a conductive semiconductor layer, or a combination of both. In this case, the absorption layer 416 is made of InGaAs.

[0059] The wide-bandgap layer 418 has a wider bandgap than the absorption layer 416 and is a semiconductor layer with a bandgap wide enough not to absorb incoming light. The wide-bandgap layer 418 is made of an intrinsic semiconductor, which is InAlGaAs, but may also be InP.

[0060] The second contact layer 420 is an InGaAs layer and is a semiconductor layer of the second conductivity type (e.g., p-type). A depletion layer forms in the wide bandgap layer 418 and the absorption layer 416 when a voltage is applied. The presence of the wide bandgap layer 418 increases the thickness of the depletion layer, reduces parasitic capacitance, and enables high-speed operation.

[0061] The convex structure 458 has the same layered structure as the mesa structure 414. The mesa structure 414 and the convex structure 458 can be formed by growing the above-described layered structure using an MBE (Molecular Beam Epitaxy) apparatus, and then separating them using lithography techniques.

[0062] The insulating film 426 covers and protects the exposed surfaces (e.g., the entire surface) of the mesa structure 414, the convex structure 458, and the first contact layer 412. The insulating film 426 is a passivation film, such as an oxide film or a nitride film, for example, a silicon oxide film or a silicon nitride film. The insulating film 426 has a first through-hole 428 in a portion of the upper surface of the first contact layer 412. The insulating film 426 has a second through-hole 430 in a portion of the upper surface of the mesa structure 414.

[0063] The semiconductor photodetector has an external electrode 456. The external electrode 456 is positioned to cover part of the top and side surfaces of the convex structure 458. The external electrode 456 and the first contact layer 412 are connected by a first through-hole 428 in the insulating film 426.

[0064] The semiconductor photodetector has a mesa electrode 436. The mesa electrode 436 is arranged in a circular shape on a portion of the upper surface of the mesa structure 414. The mesa electrode 436 and the second contact layer 420 are connected by a second through-hole 430 in the insulating film 426.

[0065] The mesa structure 414 has a shape with vertex V in the first direction D1 in plan view. The plane of the mesa structure 414 has a minimum encapsulation of a pair of vertices V in the [0-11] direction and the [01-1] direction. comprising The shape is contained within the circumference of circle C. The mesa structure 414 has no vertex V in the second direction D2 and has an arc shape.

[0066] In this embodiment as well, since no reverse tapered surface is formed on the side surface of the mesa structure 414, the coverage of the insulating film 426 covering the side surface of the mesa structure 414 is improved, and as a result, reliability can be ensured. Furthermore, because a thick wide bandgap layer 418 can be used, it becomes possible to support high-speed operation.

[0067] As a variation, the upper surfaces of the layers above the wide bandgap layer 418 (the uppermost layer and the absorption layer 416) may be made circular, creating a two-tiered mesa structure 414. Alternatively, the upper surface of the wide bandgap layer 418 may be a combination of straight lines and arcs, or a polygon such as an octagon or rhombus.

[0068] The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the configurations described in the embodiments can be replaced with substantially the same configuration, a configuration that produces the same effect, or a configuration that can achieve the same purpose.

[0069] [Summary of the Embodiment] (1) A substrate 10, a mesa structure 14 on the substrate 10 comprising multiple layers including an upper layer and a lower layer, wherein the upper layer is a light absorption layer 16 and the lower layer is a wide bandgap layer 18 with a bandgap wide enough not to absorb light, and an insulating film 26 covering the sides of the mesa structure 14, wherein each of the multiple layers is made of a single crystal of a III-V semiconductor, with the (100) plane as the upper surface, and the upper surface of the wide bandgap layer 18 has a pair of vertices V in the [0-11] direction and the [01-1] direction, with the minimum encapsulation comprising A semiconductor photodetector whose shape is contained within the circumference of circle C.

[0070] The presence of a pair of vertices V in the [0-11] and [01-1] directions makes it difficult for an inverse tapered surface to form, thus ensuring the coverage of the insulating film 26.

[0071] (2) A semiconductor photodetector as described in (1), wherein the angles of each of the pair of vertices V are 135 degrees or less.

[0072] (3) A semiconductor photodetector as described in (1) or (2), wherein the upper surface of the wide bandgap layer 18 has a pair of front ends in the

[0011] direction and the [0-1-1] direction, the minimum packaging comprising A semiconductor photodetector whose shape is contained within the circle C.

[0073] (4)(3) A semiconductor photodetector as described above, wherein the upper surface of the wide bandgap layer 18 has a shape that includes a pair of convex arcs in the

[0011] direction and the [0-1-1] direction, respectively.

[0074] (5) A semiconductor photodetector as described in (1) or (2), wherein the upper surface of the wide bandgap layer 18 has a pair of vertices V' in the

[0011] direction and the [0-1-1] direction, and the minimum encapsulation comprising A semiconductor photodetector whose shape is included on the circumference of circle C'.

[0075] A semiconductor photodetector as described in (6)(5), wherein the upper surface of the wide bandgap layer 18 is polygonal.

[0076] (7) A semiconductor photodetector as described in any one of (1) to (6), wherein the upper surface of the layer above the wide bandgap layer 18 has a pair of vertices V in the [0-11] direction and the [01-1] direction, and is minimally encapsulated. comprising A semiconductor photodetector whose shape is contained within the circumference of circle C.

[0077] (8) A semiconductor photodetector described in any one of (1) to (7), wherein the upper surface of the wide bandgap layer 18 coincides in shape with the lower surface of the absorption layer 16.

[0078] (9) A semiconductor photodetector as described in any one of (1) to (6), wherein the upper surface of the layer above the wide bandgap layer 218 is circular.

[0079] A semiconductor photodetector described in any one of items (10)(1) to (8), wherein the upper surface of the wide bandgap layer 218 protrudes from the absorption layer 216.

[0080] A semiconductor photodetector as described in any one of (1) to (10), further comprising an electrode pattern 32, wherein the electrode pattern 32 includes a mesa electrode 36 located on the upper surface of the mesa structure 14.

[0081] A semiconductor photodetector as described in (12)(11), wherein the electrode pattern 32 further includes a connecting electrode connected to the mesa electrode 36, and the connecting electrode extends in the

[0011] direction or the [0-1-1] direction.

[0082] A semiconductor photodetector as described in (13), (11), or (12), wherein the mesa electrode 36 is a semiconductor photodetector having an aperture 38 in a plan view.

[0083] A semiconductor photodetector as described in (14)(13), wherein the aperture 38 has a shape that allows signal light to be incident on it.

[0084] A semiconductor photodetector as described in (15)(14), wherein the aperture 38 is circular.

[0085] A semiconductor photodetector as described in (16)(15), wherein the mesa electrode 36 is ring-shaped in plan view.

[0086] A semiconductor photodetector as described in any one of paragraphs (1) to (12), wherein the substrate 410 has a shape that allows signal light to be incident from the side opposite to the mesa structure 414.

[0087] (18) A semiconductor photodetector described in any one of (1) to (17), wherein the wide bandgap layer 18 is thicker than the absorption layer 16.

[0088] A semiconductor photodetector described in any one of (1)(1) to (18), wherein the wide bandgap layer 18 is made of InAlGaAs, InAlAs, and InP.

[0089] A semiconductor photodetector described in any one of paragraphs (20)(1) to (19), wherein the absorption layer 16 is made of InGaAs. [Explanation of Symbols]

[0090] 10 Substrate, 12 First contact layer, 14 Mesa structure, 16 Absorption layer, 18 Wide bandgap layer, 20 Second contact layer, 22 First convex structure, 24 Second convex structure, 26 Insulating film, 28 First through-hole, 30 Second through-hole, 32 Electrode pattern, 34 First electrode, 36 Mesa electrode, 38 Aperture, 40 First external electrode, 42 First connecting electrode, 44 Second electrode, 46 Second external electrode, 48 Second connecting electrode, 214 Mesa structure, 216 Absorption layer, 218 Wide bandgap layer, 220 Second contact layer, 226 Insulating film, 250 Upper mesa structure, 252 Lower mesa structure, 314 Mesa structure, 316 Absorption layer, 318 Wide bandgap layer, 326 Insulating film, 350 Upper mesa structure, 352 Lower mesa structure, 410 Substrate, 412 414 First contact layer, 416 Mesa structure, 416 Absorption layer, 418 Wide bandgap layer, 420 Second contact layer, 426 Insulating film, 428 First through-hole, 430 Second through-hole, 436 Mesa electrode, 454 Lens, 456 External electrode, 458 Convex structure, C Minimum packaging comprising Yen, C1 minimum package comprising Yen, C2 minimum package comprising Circle, D1 first direction, D2 second direction, V vertex, V1 vertex, V2 vertex.

Claims

1. circuit board and A mesa structure is provided on the substrate, comprising multiple layers including an upper layer and a lower layer, wherein the upper layer is a light-absorbing layer and the lower layer is a wide-bandgap layer with a bandgap wide enough not to absorb the light. An insulating film covering the side surface of the mesa structure, Electrode pattern and, Equipped with, Each of the aforementioned multiple layers consists of a single crystal of a group III-V semiconductor, with the (100) plane facing upwards. The wide bandgap layer is an intrinsic semiconductor, The upper surface of the wide bandgap layer has a shape that includes a pair of vertices in the [0-11] direction and the [01-1] direction on the circumference of the smallest inclusion circle, The upper surface of the wide bandgap layer has a shape that includes a pair of convex arcs in the [011] direction and the [0-1-1] direction, and the pair of arcs are inside the minimum inclusion circle in the [011] direction and the [0-1-1] direction, The electrode pattern includes a mesa electrode on the upper surface of the mesa structure and a connecting electrode connected to the mesa electrode, wherein the connecting electrode is a semiconductor photodetector extending in the [011] direction or the [0-1-1] direction.

2. A semiconductor photodetector according to claim 1, A semiconductor photodetector in which the upper surface of the layer above the wide bandgap layer has a shape that includes a pair of vertices in the [0-11] direction and the [01-1] direction on the circumference of the smallest inclusion circle.

3. A semiconductor photodetector according to claim 1, A semiconductor photodetector in which the upper surface of the wide bandgap layer coincides in shape with the lower surface of the absorption layer.

4. A semiconductor photodetector according to claim 1, The upper surface of the layer above the wide bandgap layer is a circular semiconductor photodetector.

5. A semiconductor photodetector according to claim 1, The upper surface of the wide bandgap layer is a semiconductor photodetector protruding from the absorption layer.

6. A semiconductor photodetector according to claim 1, The mesa electrode is a semiconductor photodetector having an aperture in a plan view.

7. A semiconductor photodetector according to claim 6, The aperture is a circular semiconductor photodetector.

8. A semiconductor photodetector according to claim 7, The mesa electrode is a semiconductor photodetector that is ring-shaped in plan view.

9. A semiconductor photodetector according to claim 1, The substrate is a semiconductor photodetector having a lens formed on the side opposite to the mesa structure for focusing light incident from the outside.

10. A semiconductor photodetector according to claim 1, The wide bandgap layer is thicker than the absorption layer in the semiconductor photodetector.

11. A semiconductor photodetector according to claim 1, The wide bandgap layer is a semiconductor photodetector made of InAlGaAs, InAlAs, and InP.

12. A semiconductor photodetector according to claim 1, The absorption layer is a semiconductor photodetector made of InGaAs.

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