Optical semiconductor device

Abstract

To provide an optical semiconductor device capable of suppressing loss of optical elements.SOLUTION: An optical semiconductor device has: a first optical element formed on a silicon substrate having a first surface; and a second optical element containing a compound semiconductor, mounted on the first optical element, and having a second surface opposite to the first surface, wherein the first optical element has a first protrusion protruding toward the second surface, a part of the second surface contacts the first protrusion, and in plan view, the first protrusion is inside an outer edge of the second optical element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to optical semiconductor devices. [Background technology]

[0002] Due to the advantages of processing technology, industrial ripple effects, and miniaturization of elements, the development of silicon photonics, in which optical functional elements are formed on silicon substrates, is progressing. For example, optical integrated elements in which optical modulators or photodetectors are formed on silicon substrates are being studied.

[0003] However, silicon does not have a light-emitting mechanism, so signal light is input from an external source. Silicon also lacks the ability to amplify light. For this reason, an optical amplification mechanism separate from the silicon substrate is sometimes provided to amplify weak optical signals. For example, optical semiconductor devices are known in which optical elements such as semiconductor lasers (laser diodes: LDs) and semiconductor optical amplifiers (SOAs) are flip-chip mounted on a silicon substrate. In optical semiconductor devices with such a configuration, high-precision alignment, for example, on the submicron level, is required to achieve high coupling efficiency between the optical elements and the silicon substrate. A conventional technique has been proposed in which a structure with a pre-adjusted height is formed on a silicon substrate and this structure is used to align the optical elements in the vertical direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,816,740 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-182367 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-20180 [Non-patent literature]

[0005] [Non-Patent Document 1] Budd et al., Semiconductor Optical Amplifier (SOA) Packaging for Scalable and Gain-Integrated Silicon Photonic Switching Platforms, Electronic Components & Technology Conference 2015, p1280 Summary of the Invention [Problem to be solved by the invention]

[0006] Optical elements such as laser diodes and semiconductor optical amplifiers (SOA) are constructed using materials such as InP, which are more brittle than silicon. Therefore, with conventional technology, chipping can occur at the corners of optical elements when they come into contact with structures formed on silicon substrates. When chipping occurs at the corners, cracks can extend to key parts of the optical element, such as the waveguide, or the chipped portions can interfere with alignment. The extension of cracks and reduced alignment accuracy can lead to reduced yield and reliability.

[0007] An object of the present disclosure is to provide an optical semiconductor device that can suppress damage to optical elements. [Means for solving the problem]

[0008] According to one aspect of the present disclosure , Shi formed on a silicon substrate Has a first surface a first optical element; and a second optical element including a compound semiconductor, mounted on the first optical element, and having a second surface facing the first surface, wherein the first optical element has a first protrusion protruding toward the second surface, a part of the second surface contacting the first protrusion, and the first protrusion is located inside an outer edge of the second optical element in a plan view; the second optical element is a semiconductor optical amplifier, the second optical element has a planar shape with a first direction as a longitudinal direction, the second optical element has a second protruding portion that protrudes toward the first surface and contacts the first protruding portion, the first protruding portion has a planar shape with the first direction as a longitudinal direction, the second protruding portion has a planar shape with the first direction as a longitudinal direction, and both ends of the second protruding portion are located outside both ends of the first protruding portion in the first direction. An optical semiconductor device is provided. [Effects of the Invention]

[0009] According to the present disclosure, damage to optical elements can be suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an exploded perspective view showing an optical semiconductor device according to a first embodiment. [Figure 2] 1 is a schematic diagram showing the arrangement of each part in an optical semiconductor device according to a first embodiment. [Figure 3] 1 is a cross-sectional view (part 1) illustrating an optical semiconductor device according to a first embodiment. [Figure 4] FIG. 2 is a cross-sectional view (part 2) illustrating the optical semiconductor device according to the first embodiment. [Figure 5] FIG. 3 is a cross-sectional view (part 3) illustrating the optical semiconductor device according to the first embodiment. [Figure 6] 4A to 4C are cross-sectional views (part 1) illustrating a method for manufacturing an optical element according to the first embodiment. [Figure 7] 5A to 5C are cross-sectional views (part 2) illustrating the method for manufacturing the optical element according to the first embodiment. [Figure 8] 5A to 5C are cross-sectional views (part 3) illustrating the method for manufacturing the optical element according to the first embodiment. [Figure 9] 5A to 5C are cross-sectional views (part 4) illustrating the method for manufacturing the optical element according to the first embodiment. [Figure 10] 5 is a cross-sectional view (part 5) illustrating the method for manufacturing the optical element according to the first embodiment. [Figure 11] 6 is a cross-sectional view (part 6) illustrating the method for manufacturing the optical element according to the first embodiment. [Figure 12] 10 is a cross-sectional view (part 7) illustrating the method for manufacturing the optical element according to the first embodiment. [Figure 13] FIG. 1 is a cross-sectional view showing an optical semiconductor device according to a reference example. [Figure 14] FIG. 6 is a schematic diagram showing the arrangement of each part in an optical semiconductor device according to a second embodiment. [Figure 15] FIG. 10 is an exploded perspective view showing an optical semiconductor device according to a third embodiment. [Figure 16] FIG. 10 is a schematic diagram showing the arrangement of each part in an optical semiconductor device according to a third embodiment. [Figure 17]FIG. 10 is a cross-sectional view showing an optical semiconductor device according to a third embodiment. [Figure 18] FIG. 10 is an exploded perspective view showing an optical semiconductor device according to a fourth embodiment. [Figure 19] FIG. 10 is a schematic diagram showing the arrangement of each part in an optical semiconductor device according to a fourth embodiment. [Figure 20] FIG. 10 is a cross-sectional view showing an optical semiconductor device according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations may be designated by the same reference numerals to avoid redundant description. In the following description, an XYZ Cartesian coordinate system is used, but this coordinate system is defined for the purpose of explanation and does not limit the orientation of an optical semiconductor device or the like. An XY plane view is referred to as a planar view, and the +Z direction from an arbitrary point may be referred to as upward, upper side, or top, and the -Z direction may be referred to as downward, lower side, or bottom.

[0012] (First embodiment) A first embodiment will be described. The first embodiment relates to an optical semiconductor device. FIG. 1 is an exploded perspective view showing an optical semiconductor device according to the first embodiment. FIG. 2 is a schematic diagram showing the arrangement of each part in the optical semiconductor device according to the first embodiment. FIGS. 3 to 5 are cross-sectional views showing the optical semiconductor device according to the first embodiment. FIG. 3 corresponds to a cross-sectional view taken along line III-III in FIG. 2. FIG. 4 corresponds to a cross-sectional view taken along line IV-IV in FIG. 2. FIG. 5 corresponds to a cross-sectional view taken along line VV in FIG. 2.

[0013] 1 to 5, the optical semiconductor device 1 according to the first embodiment has a silicon photonics device 100 having a first surface 100A, and an optical element 200 having a second surface 200A. The optical element 200 includes a compound semiconductor and is mounted on the silicon photonics device 100. The second surface 200A faces the first surface 100A. In the first embodiment, the optical element 200 is a semiconductor laser (LD).

[0014] The silicon photonics device 100 has, for example, an SOI (silicon on insulator) substrate. The silicon photonics device 100 includes a silicon substrate 110, an insulating layer 120, and a silicon layer. The silicon layer has a waveguide 131 and an alignment mark 132. The waveguide 131 extends along the X-axis direction. The alignment marks 132 are provided, for example, at two locations, on the +Y side and the -Y side of the waveguide 131. The silicon layer may further include optical functional elements such as an optical modulator, an optical receiver, and a grating coupler. Modulation signal input / output electrodes, phase adjustment electrodes, etc. may be connected to the optical modulator and the optical receiver. The silicon photonics device 100 formed on the silicon substrate 110 is an example of a first optical element.

[0015] A trench 105 is formed in the SOI substrate, reaching partway through the thickness of the silicon substrate 110. The silicon photonics device 100 has an insulating layer 140 covering the SOI substrate. The insulating layer 140 also covers the sidewall and bottom surfaces of the trench 105. An electrode 150 is formed on the insulating layer 140 on the bottom surface of the trench 105. The electrode 150 has a rectangular planar shape with its longitudinal direction oriented in the X-axis direction and its lateral direction oriented in the Y-axis direction. The electrode 150 has, for example, a Ti layer 151 on the insulating layer 140, a Pt layer 152 on the Ti layer 151, and an Au layer 153 on the Pt layer 152.

[0016] The silicon substrate 110 has a protrusion 111 that protrudes from the bottom surface of the groove 105 toward the second surface 200A. The silicon photonics device 100 has a first protrusion 101 that protrudes toward the second surface 200A inside the groove 105. The first protrusion 101 includes the protrusion 111 of the silicon substrate 110 and a portion of the insulating layer 140 that covers the protrusion 111. The first protrusion 101 is provided, for example, at two locations on the +Y side and the -Y side of the electrode 150. The first protrusion 101 has a rectangular planar shape with the X-axis direction as the longitudinal direction and the Y-axis direction as the lateral direction. For example, the length of the first protrusion 101 in the X-axis direction is approximately 330 μm, and the length in the Y-axis direction is approximately 50 μm. The distance between the center of the electrode 150 in the Y-axis direction and the center of the first protrusion 101 in the Y-axis direction is approximately 167.5 μm.

[0017] The optical element 200 includes an InP substrate 210, a cladding layer 220, an active layer 230, an alignment mark 232, an insulating layer 240, an electrode 251, and an electrode 252. The cladding layer 220 is provided below the InP substrate 210, and the active layer 230 is formed within the cladding layer 220. The insulating layer 240 covers the cladding layer 220. The cladding layer 220 and the active layer 230 contain an InP-based material. The optical element 200 has a rectangular planar shape with its longitudinal direction along the X-axis and its lateral direction along the Y-axis. The cladding layer 220 includes a mesa structure 261 extending in the X-axis direction, and the active layer 230 is formed within the mesa structure 261. For example, the length of the optical element 200 in the X-axis direction is approximately 800 μm, and its length in the Y-axis direction is approximately 500 μm. The active layer 230 extends along the X-axis direction. The mesa structure 261 and the active layer 230 are provided at the center of the optical element 200 in the Y-axis direction. The active layer 230 is spaced apart from the waveguide 131 in the X-axis direction. The active layer 230 is also located at the same position as the waveguide 131 in both the Y-axis direction and the Z-axis direction. The X-axis direction is an example of a first direction. The optical element 200 is an example of a second optical element.

[0018] The cladding layer 220 has a protrusion 262 that protrudes from the surface surrounding the mesa structure 261 toward the first surface 100A. The optical element 200 has a second protrusion 202 that protrudes toward the first surface 100A. The second protrusion 202 includes the protrusion 262 of the cladding layer 220 and a portion of the insulating layer 240 that covers the protrusion 262. The second protrusion 202 is provided, for example, at two locations, one on the +Y side and one on the -Y side, of the mesa structure 261. The second protrusion 202 has a rectangular planar shape with its longitudinal direction in the X-axis direction and its lateral direction in the Y-axis direction. For example, the length of the second protrusion 202 in the X-axis direction is approximately 490 μm, and its length in the Y-axis direction is approximately 10 μm. The alignment marks 232 are provided, for example, near the +X-side end and the -X-side end of each second protrusion 202.

[0019] An opening exposing the lower surface of the cladding layer 220 is formed in the insulating layer 240, and an electrode 251 in contact with the lower surface of the cladding layer 220 is provided inside this opening. The electrode 251 is in ohmic contact with the cladding layer 220. The electrode 252 is in ohmic contact with the upper surface of the InP substrate 210. The electrode 252 is in ohmic contact with the InP substrate 210.

[0020] A portion of the second surface 200A of the optical element 200 contacts the first protrusion 101. Specifically, the surface of the second protrusion 202 facing the first protrusion 101 contacts the first protrusion 101. The width (dimension in the Y-axis direction) of the second protrusion 202 is smaller than the width (dimension in the Y-axis direction) of the first protrusion 101. As shown in FIG. 5 , in the Y-axis direction, the entire surface of the second protrusion 202 facing the first protrusion 101 contacts the first protrusion 101. On the other hand, the length (dimension in the X-axis direction) of the second protrusion 202 is greater than the length (dimension in the X-axis direction) of the first protrusion 101. 4, in the X-axis direction, a part of the surface of the second protrusion 202 facing the first protrusion 101 is in contact with the first protrusion 101, and another part of the surface of the second protrusion 202 facing the first protrusion 101 is not in contact with the first protrusion 101 and protrudes from the first protrusion 101. The second protrusion 202 protrudes from the first protrusion 101 by, for example, 80 μm on both the +X side and the −X side.

[0021] A conductive bonding material 10 is provided between the electrode 150 of the silicon photonics device 100 and the electrode 251 of the optical device 200. The electrode 150 and the electrode 251 are electrically connected via the conductive bonding material 10. The conductive bonding material 10 is, for example, AuSn solder.

[0022] In addition, in a plan view, each first protrusion 101 is located inside the outer edge of the optical element 200. That is, the +X side end of the first protrusion 101 is closer to the -X side than the +X side surface of the optical element 200, and the -X side end of the first protrusion 101 is closer to the +X side than the -X side surface of the optical element 200. In addition, the +Y side end of the first protrusion 101 is closer to the -Y side than the +Y side surface of the optical element 200, and the -Y side end of the first protrusion 101 is closer to the +Y side than the -Y side surface of the optical element 200.

[0023] Next, a method for manufacturing the optical element 200 will be described. Figures 6 to 12 are cross-sectional views showing the method for manufacturing the optical element in the first embodiment. Here, the description will be reversed from the previous description.

[0024] 6, InP-based semiconductor layers 221, 231, and 222 are formed on an InP substrate 210. The semiconductor layers 221 and 222 become part of the cladding layer 220, and the semiconductor layer 231 becomes the active layer 230. Next, insulating masks 281 and 282 are formed on the semiconductor layer 222. The mask 281 is formed in the region where the active layer 230 will be formed, and the mask 282 is formed in the region where the protrusion 262 will be formed.

[0025] 7, the semiconductor layers 221, 231, and 222 are etched using masks 281 and 282. This etching is stopped midway through the thickness of the semiconductor layer 221. As a result, the active layer 230 is formed from the semiconductor layer 231.

[0026] 8, semiconductor layers are regrown with the masks 281 and 282 remaining, to form a semiconductor layer 223 including the semiconductor layers 221 and 222. The position of the top surface of the semiconductor layer 223 is, for example, the same as the position of the top surface of the semiconductor layer 222 or close to the position of the top surface of the semiconductor layer 222.

[0027] 9, the masks 281 and 282 are removed, and further, semiconductor layers are regrown to form a semiconductor layer 224 including the semiconductor layer 223. The thickness of the semiconductor layer 224 is set to match the thickness of the cladding layer 220.

[0028] Thereafter, the semiconductor layer 224 is etched using a mask (not shown) to form a mesa structure 261, and also form a protruding portion 263 including the semiconductor layers 224 and 231 in the region where the protruding portion 262 is to be formed, as shown in Fig. 10. This etching may be performed in multiple steps.

[0029] Subsequently, the mask is removed, and etching of the protrusions 263 is performed using another mask (not shown), to form the protrusions 262 as shown in Fig. 11. In this etching, for example, the semiconductor layer 231 is removed.

[0030] Next, the mask is removed, and as shown in FIG. 12, an insulating layer 240, an electrode 251 and an electrode 252 are formed.

[0031] In this manner, the optical element 200 can be manufactured.

[0032] When the optical element 200 is flip-chip mounted on the silicon photonics element 100, the silicon photonics element 100 and the optical element 200 can be aligned in the height direction (Z-axis direction) with high precision by bringing the second protrusion 202 into contact with the first protrusion 101. Furthermore, the silicon photonics element 100 and the optical element 200 can be aligned in the XY plane with high precision by image recognition using the alignment marks 132 and 232. Therefore, the waveguide 131 and the active layer 230 can be aligned, for example, to the submicron level. During flip-chip mounting, a force is applied to the optical element 200 in a direction toward the silicon photonics element 100 until the optical element 200 is fixed to the silicon photonics element 100.

[0033] Furthermore, since the first protrusion 101 is located inside the outer edge of the optical element 200 in plan view, it is possible to suppress the occurrence of defects due to contact between the silicon photonics element 100 and the optical element 200. Here, a reference example will be described in which a part of the first protrusion is located outside the outer edge of the LD. Figure 13 is a cross-sectional view showing an optical semiconductor device according to the reference example.

[0034] The optical semiconductor device 1X according to the reference example has a silicon photonics element 100X having a first surface 100A, and an optical element 200X having a second surface 200A.

[0035] The optical element 200X does not have a second protrusion 202. The other configuration of the optical element 200X is similar to the configuration of the optical element 200. The silicon photonics element 100X has a first protrusion 101X instead of the first protrusion 101. The first protrusion 101X is provided at a position where it overlaps with the edge of the optical element 200X in a plan view, and has a height that reaches the optical element 200X. The other configuration of the silicon photonics element 100X is similar to the configuration of the silicon photonics element 100.

[0036] In the optical semiconductor device 1X, the corner where the lower surface and the side wall surface of the optical element 200X intersect is located on the first protrusion 101. For this reason, when a force is applied to the optical element 200X in a direction toward the silicon photonics element 100X during flip-chip mounting, stress tends to concentrate at the corner of the optical element 200X, and the corner is likely to be damaged.

[0037] In contrast, in the optical semiconductor device 1, the first protrusion 101 is located inside the outer edge of the optical element 200 in a plan view, so stress concentration like that in the reference example can be avoided. Although an upward force acts on the second protrusion 202, this force acts relatively uniformly, so stress concentration is unlikely to occur. Therefore, damage to the second protrusion 202 is also unlikely to occur.

[0038] As described above, according to the first embodiment, it is possible to suppress defects in the optical element 200. Therefore, it is possible to suppress cracks originating from defects from extending into the active layer 230, and to suppress a decrease in alignment accuracy. Therefore, it is possible to suppress a decrease in yield and reliability due to defects.

[0039] As described above, the semiconductor layer is regrown during the manufacture of the optical element 200 (FIG. 8). During this regrowth, abnormal growth of the semiconductor layer is likely to occur near the corner where two side surfaces of the portion that will become the protrusion 262 intersect, particularly near corners where the angle between the two side surfaces is 90°, and near side surfaces that have small dimensions parallel to the XY plane. For example, abnormal growth of the semiconductor layer is likely to occur near the end on the +X side and the end on the -X side. This is because various crystal planes exist near the portion where crystal growth occurs. Furthermore, in the portion where abnormal growth occurs, the semiconductor layer 223 is thicker than in the portion where normal crystal growth occurs. For example, the difference in thickness can be approximately 2 μm. Because this portion where abnormal growth occurs contains crystal planes that are difficult to remove by wet etching or the like, it cannot be completely removed in subsequent processes. Therefore, even after the optical element is completed, it may remain with a thickness of, for example, approximately 0.5 μm to 1 μm.

[0040] In the first embodiment, both ends of the second protrusion 202 are located outside both ends of the first protrusion 101 in the X-axis direction. Therefore, even if abnormal growth as described above occurs, the portion that has become thicker due to the abnormal growth does not come into contact with the first protrusion 101. Therefore, highly accurate alignment is possible.

[0041] In addition, in the X-axis direction, the end of the second protrusion 202 is preferably located at least 80 μm outside the end of the first protrusion 101, more preferably at least 100 μm outside, and even more preferably at least 120 μm outside.

[0042] (Second embodiment) A second embodiment will be described. The second embodiment differs from the first embodiment mainly in the shape of the end portions on both the +X side and the -Y side of the second protrusion. Fig. 14 is a schematic diagram showing the arrangement of each part in the optical semiconductor device according to the second embodiment.

[0043] As shown in FIG. 14 , in the optical semiconductor device 2 according to the second embodiment, the optical element 200 has a second protrusion 202A instead of the second protrusion 202. The end of the protrusion of the cladding layer 220 included in the second protrusion 202A on the +X side has two side surfaces inclined from both the YZ plane and the ZX plane in a planar view. These two side surfaces are crystal planes different from the (011) plane and the (0-1-1) plane. The end of the protrusion of the cladding layer 220 included in the second protrusion 202A on the -X side also has two side surfaces inclined from both the YZ plane and the ZX plane in a planar view. These two side surfaces are also crystal planes different from the (011) plane and the (0-1-1) plane. Note that, although a negative crystallographic index is usually represented by placing a "-" (bar) before the number, here a negative sign is placed before the number.

[0044] The other configurations are the same as those in the first embodiment.

[0045] The second embodiment can also achieve the same effects as the first embodiment. Furthermore, the end portions of the cladding layer 220 included in the second protrusion 202A on both the +X and -Y sides of the protrusion have two side surfaces inclined from both the YZ and ZX planes in plan view. Therefore, the angle formed by the two side surfaces at the corner is not 90°, and abnormal growth is more easily suppressed than when the angle is 90°. Furthermore, while abnormal growth is relatively likely to occur when the side surfaces are (011) or (0-1-1) planes, in the second embodiment, the side surfaces are crystal planes other than the (011) and (0-1-1) planes, which also makes it easier to suppress abnormal growth. Therefore, the second embodiment makes it easier to obtain an optical element 200 with higher dimensional accuracy.

[0046] In the present disclosure, when the planar shape of the second protrusion is a polygon, it is preferable that the angle of each vertex of the polygon is different from 90°.

[0047] (Third embodiment) A third embodiment will now be described. The third embodiment differs from the second embodiment mainly in the configuration of the optical element. FIG. 15 is an exploded perspective view showing an optical semiconductor device according to the third embodiment. FIG. 16 is a schematic diagram showing the arrangement of each part in the optical semiconductor device according to the third embodiment. FIG. 17 is a cross-sectional view showing the optical semiconductor device according to the first embodiment. FIG. 17 corresponds to a cross-sectional view taken along line XVII-XVII in FIG. 16.

[0048] In the optical semiconductor device 3 according to the third embodiment, the optical element 200 is a semiconductor optical amplifier (SOA). As shown in FIGS. 15 to 17, the optical element 200 has an active layer 330 instead of the active layer 230. The cladding layer 220 and the active layer 330 contain an InP-based material. The configuration of the cladding layer 220 may be different from that of the second embodiment. The active layer 330 extends in a direction tilted from the X-axis direction.

[0049] The silicon photonics device 100 has spot size converters (SSCs) 134 and 334. The SSC 134 is disposed near the end face on the emission side (+X side) of the active layer 330 of the optical device 200. The SSC 334 is disposed near the end face on the incidence side (-X side) of the active layer 330 of the optical device 200. The SSCs 134 and 334 are formed of, for example, a silicon nitride layer. The positions of the SSCs 134 and 334 in the Z-axis direction are the same as the position of the active layer 330 in the Z-axis direction. The silicon photonics device 100 has waveguides 133 and 333. The waveguide 133 is provided in place of the waveguide 131. The waveguides 133 and 333 are included in the silicon layer of the SOI substrate. The waveguide 133 is provided below the SSC 134. The waveguide 333 is provided below the SSC 334. In the Z-axis direction, the waveguide 133 is about 300 nm away from the SSC 134, and the waveguide 333 is about 300 nm away from the SSC 334. For example, the ends of the SSCs 134 and 334 farther from the optical element 200 are tapered to allow light to transition to the waveguides 133 and 333 with low loss. The SSCs 134 and 334 extend in a direction tilted from the X-axis direction by a larger amount than the active layer 330. The waveguides 133 and 333 extend in the same direction as the SSCs 134 and 334.

[0050] The other configurations are the same as those in the second embodiment.

[0051] The third embodiment can also provide the same effects as the second embodiment. That is, even when the optical element 200 is an SOA, effects such as suppression of damage to the optical element 200 can be obtained, similar to when the optical element 200 is an LD.

[0052] (Fourth embodiment) A fourth embodiment will be described. The fourth embodiment differs from the third embodiment in the configuration of the active layer of the SOA. FIG. 18 is an exploded perspective view showing an optical semiconductor device according to the fourth embodiment. FIG. 19 is a schematic diagram showing the arrangement of each part in the optical semiconductor device according to the fourth embodiment. FIG. 20 is a cross-sectional view showing the optical semiconductor device according to the fourth embodiment. FIG. 20 corresponds to a cross-sectional view taken along line XX-XX in FIG. 19.

[0053] As shown in FIGS. 18 to 20 , in the optical semiconductor device 4 according to the fourth embodiment, the optical element 200 has an active layer 430 instead of the active layer 330. The planar shape of the active layer 430 is U-shaped. In plan view, the active layer 430 has, for example, two linear portions extending in the X-axis direction and a semicircular portion connecting the −X-side ends of these two linear portions. For example, the distance between the two linear portions is approximately 250 μm. The optical element 200 is a so-called U-turn SOA (U-SOA). Light enters the active layer 430 and exits from the active layer 430 at the +X-side end face of the optical element 200.

[0054] The silicon photonics device 100 has an SSC 434 and a waveguide 433 instead of the SSC 334 and the waveguide 333. The SSC 434 is disposed near the end face on the incident side (+X side) of the active layer 330 of the optical device 200. The SSC 434 is formed of, for example, a silicon nitride layer. The positions of the SSCs 134 and 434 in the Z-axis direction are the same as the position of the active layer 430 in the Z-axis direction. The waveguide 433 is included in the silicon layer of the SOI substrate. The waveguide 433 is provided below the SSC 334. In the Z-axis direction, the waveguide 433 is spaced about 300 nm from the SSC 434. For example, the end of the SSC 434 farther from the optical device 200 has a tapered shape to allow light to transition to the waveguide 433 with low loss. The SSC 434 extends in a direction tilted from the X-axis direction by a larger amount than the active layer 330. The waveguide 433 extends in the same direction as the SSC 434 .

[0055] The other configurations are the same as those of the third embodiment.

[0056] The fourth embodiment can also achieve the same effects as the third embodiment. Moreover, since both SSCs 334 and 434 are located on the +X side of the optical element 200, it is possible to further suppress miscoupling due to a slight rotation or tilt of the optical element 200 compared to the third embodiment. Therefore, it is possible to reduce coupling loss more stably.

[0057] The compound semiconductor included in the second optical element is not limited to an InP-based semiconductor, and a GaAs-based semiconductor may be included in the second optical element. For example, the second optical element may have a GaAs substrate and a semiconductor layer including a GaAs-based semiconductor.

[0058] The above describes in detail preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0059] Various aspects of the present disclosure are summarized below as appendices.

[0060] (Appendix 1) a first optical element formed on a silicon substrate having a first surface; a second optical element including a compound semiconductor, mounted on the first optical element, and having a second surface opposite to the first surface; and the first optical element has a first protrusion that protrudes toward the second surface, a portion of the second surface contacts the first protrusion, 10. An optical semiconductor device, wherein, in a plan view, the first protrusion is located inside the outer edge of the second optical element. (Appendix 2) the second optical element has a planar shape with a first direction as a longitudinal direction, 2. The optical semiconductor device according to claim 1, wherein the first protrusion has a planar shape with the first direction as a longitudinal direction. (Appendix 3) 3. The optical semiconductor device according to claim 2, wherein the second optical element has an active layer extending in the first direction. (Appendix 4) the second optical element has a second protruding portion that protrudes toward the first surface and is in contact with the first protruding portion; the second protrusion has a planar shape with the first direction as a longitudinal direction, 3. The optical semiconductor device according to claim 2, wherein both ends of the second protrusion are located outside both ends of the first protrusion in the first direction. (Appendix 5) the second protrusion has a polygonal planar shape, 5. The optical semiconductor device according to claim 4, wherein the angle of each vertex of the polygon is deviated from 90°. (Appendix 6) 5. The optical semiconductor device according to claim 4, wherein the end of the second protrusion is positioned 80 μm or more outward from the end of the first protrusion in the first direction. (Appendix 7) 7. The optical semiconductor device according to claim 1, wherein the second optical element is flip-chip mounted on the first optical element. (Appendix 8) 7. The optical semiconductor device according to claim 1, wherein the second optical element is a semiconductor laser. (Appendix 9) 7. The optical semiconductor device according to claim 1, wherein the second optical element is a semiconductor optical amplifier. (Appendix 10) 10. The optical semiconductor device according to any one of claims 1 to 9, wherein the second optical element includes an InP-based material or a GaAs-based material. [Explanation of symbols]

[0061] 1, 2, 3, 4: Optical semiconductor device 100: Silicon photonics device 100A: Side 1 101:First protrusion 105: Groove 110: Silicon substrate 120: Insulating layer 131, 133, 333, 433: Waveguide 134, 334, 434: Spot size converter 140: Insulating layer 200: Optical element 200A: 2nd side 202, 202A: Second protrusion 210: InP substrate 220: Cladding layer 230, 330, 430: active layer 240: Insulating layer 261: Mesa structure 262:Protrusion

Claims

1. A first optical element having a first surface formed on a silicon substrate; a second optical element including a compound semiconductor, mounted on the first optical element, and having a second surface opposite to the first surface; and the first optical element has a first protrusion that protrudes toward the second surface, a portion of the second surface contacts the first protrusion; the first protrusion is located inside an outer edge of the second optical element in a plan view; the second optical element is a semiconductor optical amplifier; the second optical element has a planar shape with a first direction as a longitudinal direction, the second optical element has a second protruding portion that protrudes toward the first surface and is in contact with the first protruding portion; the first protrusion has a planar shape with the first direction as a longitudinal direction, the second protrusion has a planar shape with the first direction as a longitudinal direction, The optical semiconductor device according to claim 1, wherein both ends of the second protrusion are located outside both ends of the first protrusion in the first direction.

2. 2. The optical semiconductor device according to claim 1, wherein the second optical element is flip-chip mounted on the first optical element.

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