Light receiving element and method of manufacturing light receiving element

Abstract

To provide a light receiving element and a method of manufacturing the light receiving element, which can reduce the loss of light.SOLUTION: A light receiving element includes: a substrate including a silicon layer; and a photodiode formed of a III-V group compound semiconductor and bonded to the silicon layer. The silicon layer includes a waveguide, and the photodiode includes a first semiconductor layer, a light absorbing layer, and a second semiconductor layer. The first semiconductor layer is in contact with the silicon layer, and the light absorbing layer and the second semiconductor layer are stacked in this order on a surface, of the first semiconductor layer, opposite to the silicon layer. The first semiconductor layer has a first conductivity type, and the second semiconductor layer has a second conductivity type. The first semiconductor layer includes a projecting portion and a first slab portion, and the projecting portion is connected to the first slab portion and projects, from the first slab portion, to a position overlapping with the waveguide.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present disclosure relates to a light receiving element and a method for manufacturing the light receiving element. [Background technology]

[0002] A hybrid photodetector can be formed by bonding a photodiode made of a III-V compound semiconductor to a substrate such as an SOI (Silicon On Insulator) substrate (silicon photonics) on which a waveguide is formed (see, for example, Non-Patent Document 1). The photodiode absorbs light propagated through the waveguide and outputs an electrical signal. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Ye Wang,et al. “High-Power Photodiodes With 65 GHz Bandwidth Heterogeneously Integrated Onto Silicon-on-Insulator Nano-Waveguides” IEEE Journal of Selected Topics in Quantum Electronics,Vol.24,No.2,6000206,March / April,2018 Summary of the Invention [Problem to be solved by the invention]

[0004] Optical loss occurs between the waveguide of the substrate and the bonded photodiode. Reducing the optical loss can improve the light-receiving sensitivity. Therefore, the object of the present invention is to provide a light-receiving element capable of reducing optical loss and a method for manufacturing the light-receiving element. [Means for solving the problem]

[0005] A light-receiving element according to the present disclosure comprises a substrate having a silicon layer, and a photodiode formed of a III-V compound semiconductor and bonded to the silicon layer, the silicon layer having a waveguide, the photodiode including a first semiconductor layer, a light absorption layer, and a second semiconductor layer, the first semiconductor layer being in contact with the silicon layer, the light absorption layer and the second semiconductor layer being stacked in this order on a surface of the first semiconductor layer opposite the silicon layer, the first semiconductor layer having a first conductivity type, and the second semiconductor layer having a second conductivity type, the first semiconductor layer having a protrusion and a first slab portion, the protrusion being connected to the first slab portion and protruding from the first slab portion to a position overlapping with the waveguide. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide a light receiving element capable of reducing light loss and a method for manufacturing the light receiving element. [Brief explanation of the drawings]

[0007] [Figure 1A] FIG. 1A is a top view illustrating the light-receiving element according to the first embodiment. [Figure 1B] FIG. 1B is a perspective view illustrating an example of a light receiving element. [Figure 1C] FIG. 1C is an enlarged view of the protrusion. [Figure 2A] FIG. 2A is a cross-sectional view illustrating an example of a light receiving element. [Figure 2B] FIG. 2B is a cross-sectional view illustrating an example of a light receiving element. [Figure 3] FIG. 3 is a diagram illustrating the loss of light. [Figure 4A] FIG. 4A is a plan view illustrating a method for manufacturing a light-receiving element. [Figure 4B] FIG. 4B is a plan view illustrating a method for manufacturing the light-receiving element. [Figure 4C] FIG. 4C is a plan view illustrating a method for manufacturing the light-receiving element. [Figure 5A] FIG. 5A is a plan view illustrating a protrusion of a light receiving element according to Modification 1. FIG. [Figure 5B] FIG. 5B is a plan view illustrating a protruding portion of a light receiving element according to Modification 2. As shown in FIG. [Figure 5C] FIG. 5C is a plan view illustrating a protrusion of a light receiving element according to Modification 3. As shown in FIG. [Figure 5D] FIG. 5D is a plan view illustrating a protrusion of a light receiving element according to Modification 4. As shown in FIG. [Figure 6A] FIG. 6A is a perspective view illustrating a light-receiving element according to the second embodiment. [Figure 6B] FIG. 6B is a diagram illustrating the loss of light. [Figure 7] FIG. 7 is a perspective view illustrating a light-receiving element according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0009] One aspect of the present disclosure provides a light-receiving element (1) comprising: a substrate having a silicon layer; and a photodiode formed of a III-V compound semiconductor and bonded to the silicon layer, the silicon layer having a waveguide; the photodiode including a first semiconductor layer, a light-absorbing layer, and a second semiconductor layer, the first semiconductor layer contacting the silicon layer, the light-absorbing layer and the second semiconductor layer stacked in this order on a surface of the first semiconductor layer opposite the silicon layer, the first semiconductor layer having a first conductivity type, the second semiconductor layer having a second conductivity type, the first semiconductor layer having a protrusion and a first slab portion, the protrusion being connected to the first slab portion and protruding from the first slab portion to a position overlapping with the waveguide. Because the photodiode has the protrusion, light is less likely to be reflected and scattered at the interface between the waveguide and the photodiode, thereby reducing light loss. (2) In the above (1), the protrusion may have a first tapered portion, and the first tapered portion may have a shape tapered along the extension direction of the waveguide. Light gradually transitions from the waveguide to the photodiode. This can effectively reduce light loss. (3) In the above (1) or (2), the length of the protrusion may be 2 μm or more, which can reduce light loss. (4) In any of the above (1) to (3), the tip of the protrusion may be curved. Since light is less likely to be reflected, loss of light can be reduced. (5) In any one of (1) to (4) above, the photodiode may have a mesa, the mesa including the light absorption layer and the second semiconductor layer, located on the first slab portion, and facing the protrusion in the extension direction of the waveguide. Light propagates through the waveguide, transitions to the photodiode at the protrusion, and is absorbed in the light absorption layer of the mesa. The photodiode can detect the light. (6) In the above (5), the mesa may have a second tapered portion, and the second tapered portion may have a shape tapered along the extending direction of the waveguide. This can reduce optical loss. (7) In the above (6), the length of the second tapered portion may be 5 μm or more, which can reduce optical loss. (8) In the above (5), the silicon layer may have a recess and a second slab portion, the recess being recessed from the second slab portion and located on both sides of the waveguide, the waveguide being connected to an end of the second slab portion, and the first slab portion of the photodiode being bonded to the second slab portion. Light is absorbed by the photodiode on the second slab portion. Light can be detected. (9) In the above (8), the second slab portion may protrude outward from the first slab portion, and the waveguide may protrude outward from the protruding portion. Even if a liquid such as an etchant enters the recess, the bottom surface of the photodiode is unlikely to come into contact with the liquid. This makes it possible to prevent etching from the bottom surface. (10) A method for manufacturing a light-receiving element, comprising the steps of: bonding a photodiode formed of a III-V compound semiconductor to a silicon layer of a substrate; and forming a slab portion and a protrusion in the photodiode, wherein the silicon layer has a waveguide; the photodiode includes a first semiconductor layer, a light absorption layer, and a second semiconductor layer, the first semiconductor layer contacting the silicon layer, the light absorption layer and the second semiconductor layer being stacked in this order on the surface of the first semiconductor layer opposite the silicon layer, the first semiconductor layer having a first conductivity type, the second semiconductor layer having a second conductivity type, the first semiconductor layer having the protrusion and the slab portion, the protrusion being connected to the slab portion and protruding from the slab portion to a position overlapping with the waveguide. Because the photodiode has the protrusion, light is less likely to be reflected or scattered at the interface between the waveguide and the photodiode, thereby reducing light loss.

[0010] [Details of the embodiments of the present disclosure] Specific examples of a light-receiving element and a method for manufacturing a light-receiving element according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0011] First Embodiment (photodetector) FIG. 1A is a top view illustrating a light-receiving element 100 according to the first embodiment. FIG. 1B is a perspective view illustrating the light-receiving element 100. FIG. 1C is an enlarged view of a protrusion 50. Insulating films are omitted from FIGS. 1A to 1C. Electrodes are omitted from FIG. 1B. FIGS. 2A and 2B are cross-sectional views illustrating the light-receiving element 100. FIG. 2A illustrates a cross-section taken along line AA in FIG. 1A. FIG. 2B illustrates a cross-section taken along line BB in FIG. 1A.

[0012] As shown in FIGS. 1A and 1B, the light receiving element 100 is a hybrid light receiving element and includes a substrate 10 and a photodiode 30. The photodiode 30 is bonded to the upper surface of the substrate 10. The Z-axis direction is the normal direction to the upper surface of the substrate 10. The X-axis direction is parallel to the waveguide. The Y-axis direction is perpendicular to the X-axis and Z-axis directions.

[0013] The substrate 10 has a waveguide 20, a recess 22, a terrace 24, and a slab portion 26 (second slab portion). The waveguide 20 and the recess 22 are parallel to the X-axis direction. The recess 22 is provided on both sides of the waveguide 20 in the Y-axis direction. The terrace 24 is provided outside the recess 22.

[0014] In FIG. 1A, a waveguide 20, a recess 22, and a terrace 24 are provided on the left side. A slab portion 26 is provided on the right side. The terrace 24 and the slab portion 26 are planar. In the X-axis direction, the waveguide 20 and the recess 22 extend from one end of the substrate 10 to a position where they overlap with the photodiode 30. The waveguide 20 is connected to one end of the slab portion 26. In the Y-axis direction, the slab portion 26 has a width greater than that of the waveguide 20 and is connected to the waveguide 20 and the terrace 24.

[0015] As shown in FIGS. 2A and 2B, substrate 10 is an SOI (Silicon on Insulator) substrate and includes substrate 12, box layer 14, and silicon (Si) layer 16, which are stacked in this order in the Z-axis direction. Substrate 12 is made of, for example, Si. Box layer 14 is made of, for example, silicon oxide (SiO2). Box layer 14 has a thickness of, for example, 3 μm. Silicon layer 16 has a thickness of, for example, 220 nm. The upper surface of substrate 10 and the surface of photodiode 30 are covered with insulating film 11. Insulating film 11 is made of, for example, SiO2 with a thickness of 1 μm. Silicon layer 16 has a refractive index of 3.45. The refractive indexes of box layer 14 and insulating film 11 are 1.45, lower than that of silicon layer 16. These refractive indices are values ​​for light with a wavelength of 1.55 μm. Silicon layer 16 of substrate 10 is provided with waveguide 20, recess 22, terrace 24, and slab portion 26.

[0016] The waveguide 20, the terrace 24, and the slab portion 26 protrude in the Z-axis direction (upward) beyond the recess 22. The surfaces of the waveguide 20, the terrace 24, and the slab portion 26 are located at the same height. The recess 22 is recessed below the surfaces of the waveguide 20, the terrace 24, and the slab portion 26. The silicon layer 16 forms the bottom surface of the recess 22. The thickness of the silicon layer 16 in the recess 22 is, for example, 30 nm. The recess 22 may extend partway through the silicon layer 16 in the Z-axis direction, or may extend through the silicon layer 16 to the box layer 14. An insulating film 11 is buried in the recess 22.

[0017] The photodiode 30 is a semiconductor element made of a III-V compound semiconductor. The photodiode 30 is bonded to the terrace 24 and slab portion 26 of the silicon layer 16. As shown in FIGS. 1B and 2B , the photodiode 30 has a semiconductor layer 32 (first semiconductor layer), a light absorption layer 34, a semiconductor layer 36 (second semiconductor layer), and a contact layer 38. The semiconductor layer 32 is in contact with the silicon layer 16 of the substrate 10. The light absorption layer 34, the semiconductor layer 36, and the contact layer 38 are stacked in this order on the surface of the semiconductor layer 32 opposite the substrate 10.

[0018] The semiconductor layer 32 is formed of, for example, n-type (first conductivity type) indium phosphide (n-InP). The semiconductor layer 32 is doped with, for example, silicon (Si). The light absorption layer 34 is formed of, for example, undoped indium gallium arsenide (InGaAs). The semiconductor layer 36 is formed of, for example, p-type (second conductivity type) indium phosphide (p-InP). The contact layer 38 is formed of, for example, p+-type indium gallium arsenide ((p+)-InGaAs). The semiconductor layer 36 and the contact layer 38 are doped with, for example, zinc (Zn). The semiconductor layers of the photodiode 30 may be formed of III-V compound semiconductors other than those mentioned above.

[0019] 1A and 1B, the photodiode 30 has a protrusion 50, a slab 52 (first slab), and a mesa 54. As shown in FIG. 1B, the protrusion 50 and the slab 52 include a semiconductor layer 32. The mesa 54 includes a light absorption layer 34, a semiconductor layer 36, and a contact layer 38. As shown in FIG. 2A, the protrusion 50 is covered with an insulating film 11. As shown in FIG. 2B, the slab 52 and the mesa 54 are also covered with an insulating film 11.

[0020] As shown in FIGS. 1A and 1B, the slab portion 52 is provided over a wider area than the mesa 54 and is bonded to the terrace 24 and slab portion 26 of the silicon layer 16. The width of the slab portion 52 is greater than the width of the protruding portion 50. The protruding portion 50 is connected to one end of the slab portion 52 and protrudes from that end to a position overlapping with the waveguide 20. The entire protruding portion 50 is a tapered portion (first tapered portion) and has a tapered shape along the X-axis direction. The width of the protruding portion 50 increases toward the slab portion 52 and decreases away from the slab portion 52. As shown in FIG. 1C, the width W1 of the portion of the protruding portion 50 connected to the slab portion 52 is, for example, 2 μm. The length L1 of the protruding portion 50 in the X-axis direction is, for example, 2 μm or more and 100 μm or less. The tip of the protruding portion 50 is curved. The protruding portion 50 is symmetrical with respect to the X-axis direction.

[0021] The mesa 54 is located on the slab portion 52 and faces the protruding portion 50 in the X-axis direction. The mesa 54 has a rectangular parallelepiped shape. As shown in FIG. 1B, the length L2 of the mesa 54 is, for example, 5 μm or more and 50 μm or less, and is, for example, 30 μm. The width W2 of the mesa 54 is, for example, 0.5 μm or more and 6 μm or less, and is, for example, 2 μm. The waveguide 20 extends to the end of the mesa 54 opposite the protruding portion 50. The n-type semiconductor layer 32, the light absorption layer 34, and the p-type semiconductor layer 36 form a pin junction.

[0022] As shown in FIG. 1A, the light-receiving element 100 has electrodes 40 and 42, and pads 44 and 46. The electrodes and pads are made of metal. The two electrodes 40 are cathodes and are electrically connected to the semiconductor layer 32. The pad 44 is electrically connected to the electrode 40. The electrode 42 is an anode and is electrically connected to the contact layer 38. The pad 46 is electrically connected to the electrode 42.

[0023] The length L3 of pad 46 in the X-axis direction is, for example, not less than 50 μm and not more than 150 μm. The width W3 of pad 46 in the Y-axis direction is, for example, not less than 50 μm and not more than 100 μm. The size of pad 44 is, for example, the same as that of pad 46. The center-to-center distance D1 between pads 44 and 46 is, for example, not less than 100 μm and not more than 200 μm.

[0024] The light receiving element 100 detects light propagating through the waveguide 20. The wavelength of the light to be detected is, for example, 1.55 μm, but may be 1.26 μm or more and 1.63 μm or less. A reverse bias voltage is applied to the photodiode 30 using pads 44 and 46. The substrate 10 and the photodiode 30 are evanescently optically coupled. The light propagates through the waveguide 20 and transitions from the waveguide 20 to the photodiode 30. The light absorption layer 34 of the photodiode 30 absorbs the light and generates photocarriers (hole-electron pairs). The photocarriers are output as a photocurrent.

[0025] The photodiode 30 has a tapered protrusion 50. Light transits from the waveguide 20 to the photodiode 30 at the protrusion 50. The provision of the protrusion 50 reduces the reflection and scattering of light between the waveguide 20 and the photodiode 30, reducing light loss. The photodiode 30 absorbs high-power light, improving light-receiving sensitivity.

[0026] The mode of light propagating through the waveguide 20 is single mode. Higher-order modes may occur in the protrusion 50. The photodiode 30 can absorb light in single mode and higher-order modes and output an electrical signal.

[0027] FIG. 3 is a diagram illustrating optical loss. The horizontal axis represents the length L1 of the protrusion 50. 0 on the horizontal axis in FIG. 3 represents an example in which the photodiode 30 does not have the protrusion 50. When the length L1 is greater than 0, the photodiode 30 has the protrusion 50. The vertical axis represents the calculation results of the optical loss at the interface between the waveguide 20 and the photodiode 30. The wavelength of light used in the loss calculation is 1.55 μm in a vacuum. The approximate wavelength of light propagating through the silicon layer 16 is the wavelength in a vacuum divided by the refractive index of the silicon layer 16. The protrusion 50 has a tapered shape. The width W1 of the protrusion 50 is set to 2 μm.

[0028] When the length L1 is 0, the optical loss is 0.14 dB. The photodiode 30 has the protrusion 50, which reduces the optical loss. When the length L1 of the protrusion 50 is 2 μm or more, the optical loss is reduced to around 0.02 dB. When the length L1 of the protrusion 50 is longer than four times the wavelength of the light in the protrusion 50, the optical loss is small, at 0.02 dB or less. When the length L1 is in the range of 6 μm or more and 50 μm or less, the optical loss is 0.02 dB or less.

[0029] (Manufacturing method) The silicon layer 16 of the substrate 10 is subjected to, for example, dry etching. The portions exposed by the mask (not shown) are etched to form recesses 22. The portions covered by the mask (not shown) are not etched. The waveguide 20, the terrace 24, and the slab portion 26 are formed.

[0030] A contact layer 38, a semiconductor layer 36, a light absorption layer 34, and a semiconductor layer 32 are epitaxially grown in this order on an InP substrate separate from the SOI substrate (substrate 10) by metal organic chemical vapor deposition (MOCVD) or the like. This InP substrate is then diced to form the photodiode 30. The photodiode 30 immediately after dicing is a rectangular parallelepiped, and does not have the protrusion 50 or the mesa 54.

[0031] 4A to 4C are plan views illustrating a method for manufacturing a light-receiving element 100. As shown in FIG. 4A, a photodiode 30 is bonded to the upper surface of a substrate 10. In the bonding process, plasma is irradiated onto one surface of the silicon layer 16 and the surface of the semiconductor layer 32 of the photodiode 30 to activate these surfaces. The surface of the semiconductor layer 32 is brought into contact with the surface of the silicon layer 16, and the photodiode 30 is bonded to the silicon layer 16. For example, the photodiode 30 covers the entire upper surface of the silicon layer 16 and is located above the waveguide 20, recess 22, terrace 24, and slab portion 26. After bonding, wet etching is performed to remove the InP substrate from the photodiode 30. The contact layer 38 to the semiconductor layer 32 remain.

[0032] As shown in FIG. 4B, a mesa 54 is formed in the photodiode 30. Portions of the contact layer 38, the semiconductor layer 36, and the light absorption layer 34 that are exposed through a mask (not shown) are removed by dry etching. The mesa 54 is formed in the portion covered by the mask. For example, a chlorine-based etching gas is used in the dry etching. After the dry etching, the mask is removed. The semiconductor layer 32 of the photodiode 30 covers the upper surface of the substrate 10.

[0033] As shown in FIG. 4C, a slab portion 52 and a protrusion portion 50 are formed in the photodiode 30. The mesa 54 and a portion of the semiconductor layer 32 are covered with a mask (not shown). The portion of the semiconductor layer 32 exposed from the mask is removed by dry etching. The slab portion 52 and the protrusion portion 50 are formed by dry etching. After dry etching, the mask is removed.

[0034] The electrodes 40 and 42, and the pads 44 and 46 are provided by vacuum deposition and lift-off. The substrate 10 is cut to form the light-receiving elements 100.

[0035] According to the first embodiment, the photodiode 30 is bonded to the substrate 10. The semiconductor layer 32 of the photodiode 30 has a protrusion 50. The protrusion 50 protrudes toward the waveguide 20. Since the photodiode 30 has the protrusion 50, light is less likely to be reflected and scattered at the interface between the waveguide 20 and the photodiode 30. This reduces light loss. Since the photodiode 30 can absorb high-power light, the light-receiving sensitivity of the light-receiving element 100 is improved.

[0036] As shown in Figures 1A to 1C, the protrusion 50 is a tapered portion. The refractive index changes continuously along the X-axis direction. Light gradually transitions from the waveguide 20 to the photodiode 30. This can effectively reduce light loss.

[0037] As shown in FIG. 3, when the length L1 of the protrusion 50 is 2 μm or more, optical loss can be significantly reduced. When the length L1 is in the range of 6 μm or more and 50 μm or less, the optical loss is 0.02 dB or less. In the example of FIG. 3, even if the protrusion 50 is lengthened to 20 μm or more, the optical loss remains approximately the same. For example, the length L1 may be 2 μm or more and 20 μm or less. The length L1 may be 1.5 μm or more, 3 μm or more, 5 μm or more, or 10 μm or more, and 20 μm or less, or 30 μm or less.

[0038] As shown in FIG. 1C, the tip of the protrusion 50 is curved. In plan view, the tip is arc-shaped or elliptical arc-shaped. The tip of the protrusion 50 is not perpendicular to the direction of light propagation. Light is less likely to be reflected by the tip of the protrusion 50, and can more easily reach the photodiode 30. This reduces light loss.

[0039] In the waveguide 20, the optical mode is, for example, a single mode. The photodiode 30 can absorb both single mode and higher-order modes. Therefore, higher-order modes may be excited at the protrusion 50. Higher-order modes spread over a wider area in the cross section of the photodiode 30 than single mode. Light containing multiple higher-order modes is widely distributed in the cross section from the semiconductor layer 32 to the semiconductor layer 36. The optical intensity is not localized in the light absorption layer 34. Since the optical intensity is not localized, photocarriers are also not localized. The photodiode 30 has high responsiveness not only to low-frequency optical signals but also to high-frequency optical signals. For example, the photodetector 100 can effectively operate at high speeds of 50 GHz or more.

[0040] The semiconductor layer 32 of the photodiode 30 is in contact with the silicon layer 16 of the substrate 10. No layer such as a resin is provided between the photodiode 30 and the silicon layer 16. This can reduce light loss.

[0041] The photodiode 30 has a protrusion 50, a slab 52, and a mesa 54. The protrusion 50 overlaps the waveguide 20. The mesa 54 faces the protrusion 50 in the extension direction of the waveguide 20. Light propagating through the waveguide 20 transits to the photodiode 30 at the protrusion 50 and is absorbed by the light absorption layer 34 of the mesa 54. The photodiode 30 can detect light.

[0042] The protrusion 50 and the slab 52 are formed of an n-type semiconductor layer 32. The mesa 54 includes a light-absorbing layer 34, a p-type semiconductor layer 36, and a contact layer 38. A pin junction is formed in the photodiode 30. The light-absorbing layer 34 absorbs light and generates photocarriers. The photocarriers are output. The light can be detected by the photodetector 100.

[0043] Parasitic capacitance occurs in the mesa 54. The larger the mesa 54, the higher the parasitic capacitance. In a plan view, the area of ​​the mesa 54 is smaller than the area of ​​the slab portion 52. Because the mesa 54 is small, the parasitic capacitance is reduced. This reduces the impact on the operation of the light-receiving element 100.

[0044] The semiconductor layer 32 is formed of, for example, n-InP. The semiconductor layer 36 is formed of, for example, p-InP. The light absorption layer 34 is formed of, for example, InGaAs. The semiconductor layer 32, the semiconductor layer 36, and the light absorption layer 34 may contain compound semiconductors other than those mentioned above. The semiconductor layer 32 may be p-type, and the semiconductor layer 36 and the contact layer 38 may be n-type.

[0045] The silicon layer 16 of the substrate 10 has a waveguide 20, a recess 22, a terrace 24, and a slab portion 26. The waveguide 20 is connected to an end of the slab portion 26. A slab portion 52 of a photodiode 30 is bonded to the slab portion 26. Light propagating through the waveguide 20 is transferred to the photodiode 30 and absorbed by the photodiode 30 on the slab portion 26. The light receiving element 100 can detect the light.

[0046] (Modification 1 and Modification 2) FIG. 5A is a plan view illustrating a protrusion 50 of a light-receiving element according to Modification 1. FIG. 5B is a plan view illustrating a protrusion 50 of a light-receiving element according to Modification 2. Description of the same configuration as in the first embodiment will be omitted. As shown in FIG. 5A, in Modification 1, the tip of the protrusion 50 is a plane perpendicular to the X-axis. As shown in FIG. 5B, in Modification 2, the tip of the protrusion 50 is an inclined surface that is inclined with respect to the X-axis direction and the Y-axis direction. The protrusion 50 is asymmetric with respect to the X-axis direction.

[0047] In both Modifications 1 and 2, the photodiode 30 has the protrusion 50, which reduces light loss. If the surface at the tip of the protrusion 50 is perpendicular to the light propagation direction (X-axis direction) as in Fig. 5A, there is a risk that the light will be reflected from that surface. If the tip of the protrusion 50 is inclined with respect to the X-axis direction as in Fig. 5B, the light is less likely to be reflected.

[0048] (Modification 3 and Modification 4) FIG. 5C is a plan view illustrating a protrusion 50 of a light-receiving element according to Modification 3. FIG. 5D is a plan view illustrating a protrusion 50 of a light-receiving element according to Modification 4. Description of the same configuration as in the first embodiment will be omitted. As shown in FIG. 5C, in Modification 3, the protrusion 50 has a portion 53 and a tapered portion 55. The planar shape of portion 53 is linear. The tapered portion 55 is located at the tip of the protrusion 50 and has a tapered shape. As shown in FIG. 5D, in Modification 4, the entire protrusion 50 is linear.

[0049] In Modifications 3 and 4, the photodiode 30 also has the protrusion 50, which reduces light loss. If the entire protrusion 50 were linear, as in FIG. 5D, there is a risk of light loss. Furthermore, the tip surface is perpendicular to the light propagation direction, which may increase reflection. As in FIG. 5C, the protrusion 50 has a tapered portion 55, which allows the light to gradually transition from the waveguide 20 to the photodiode 30. This reduces light loss. As in FIG. 1C, the entire protrusion 50 may be tapered. It is sufficient that at least a portion of the protrusion 50 is tapered.

[0050] Second Embodiment FIG. 6A is a perspective view illustrating a light-receiving element 200 according to the second embodiment. Description of the same configuration as in the first embodiment will be omitted. As shown in FIG. 6A, the mesa 54 of the photodiode 30 has a tapered portion 56 (second tapered portion). The tapered portion 56 is located in a portion of the mesa 54 close to the waveguide 20, and tapers along the extension direction of the waveguide 20. In the X-axis direction, the portion of the waveguide 20 located outside the photodiode 30, the protrusion 50, and the tapered portion 56 are aligned in this order.

[0051] According to the second embodiment, the semiconductor layer 32 has a protruding portion 50. The mesa 54 has a tapered portion 56. The photodiode 30 has a two-step tapered structure, which can improve the optical coupling efficiency between the waveguide 20 and the light absorption layer 34. It can also reduce optical loss.

[0052] FIG. 6B is a diagram illustrating optical loss. The horizontal axis represents the length L1 of the protrusion 50. The vertical axis represents the calculation results of the optical loss at the interface between the waveguide 20 and the photodiode 30. The protrusion 50 has a tapered shape. The width W1 of the protrusion 50 is 2 μm. The length L1 of the protrusion 50 of the semiconductor layer 32 and the length L4 of the tapered portion 56 of the mesa 54 in the X-axis direction are varied. The black circles and solid lines represent an example where the length L4 is 0. The dashed lines and squares represent an example where the length L4 is 5 μm. The solid lines and diamonds represent an example where the length L4 is 10 μm. The dashed line and double circles represent an example where the length L4 is 15 μm. The dotted line and triangles represent an example where the length L4 is 20 μm.

[0053] As shown in FIG. 6B, by setting the length L4 of the tapered portion 56 to, for example, 5 μm or more and 20 μm or less, optical loss can be reduced compared to when the tapered portion 56 is not provided (L4 = 0). When comparing cases where the length L1 of the protrusion 50 is the same, the longer the tapered portion 56, the lower the optical loss. Regardless of the value of length L4, when the length L1 of the protrusion 50 is in the range of 7 μm or more and 50 μm or less, the optical loss is 0.02 dB or less. The length of the mesa 54 in the X-axis direction is 30 μm. If the length L4 of the tapered portion 56 is increased while keeping the length of the mesa 54 constant, the area of ​​the mesa 54 in plan view will be reduced. This will reduce the volume of the light absorption layer 34. This may result in insufficient optical absorption in the photodiode 30. The length L4 may be equal to or less than the length L2 of the mesa 54 so that the photodiode 30 can sufficiently absorb light.

[0054] Third Embodiment 7 is a perspective view illustrating a light receiving element 300 according to the third embodiment. Description of the same configuration as in the first or second embodiment will be omitted.

[0055] 7, the slab portion 26 of the substrate 10 is located over a wider area than the slab portion 52 of the photodiode 30, and protrudes outward from the slab portion 52 in the X-axis and Y-axis directions. The waveguide 20 and the recess 22 extend to the ends of the slab portion 52, but do not extend to a position where they overlap with the slab portion 26. In other words, the slab portion 52 is not exposed to the recess 22.

[0056] The waveguide 20 has a tapered portion 21. The width of the tapered portion 21 increases as it approaches the slab portion 26 and decreases as it moves away from the slab portion 26. The portion of the waveguide 20 other than the tapered portion 21 has a constant width. The protruding portion 50 of the photodiode 30 has a tapered shape and is joined to the tapered portion 21 of the waveguide 20. The width of the tapered portion 21 is greater than the width of the protruding portion 50. The waveguide 20 protrudes outward from the protruding portion 50. The entire protruding portion 50 is located above the tapered portion 21 and is not exposed in the recess 22.

[0057] The mesa 54 of the photodiode 30 has a tapered portion 56. The tapered portion 56 is located on the protrusion 50. The non-tapered portion of the mesa 54 is located on the slab portion 52.

[0058] According to the third embodiment, the slab portion 52 of the photodiode 30 is bonded to the slab portion 26 of the silicon layer 16. The slab portion 26 protrudes outward from the slab portion 52. The waveguide 20 protrudes outward from the protrusion 50. The photodiode 30 is not exposed in the recess 22. In other words, the entire lower surface of the photodiode 30 is in contact with the silicon layer 16. Even if gases such as etching gases used in dry etching and liquids such as etchants enter the recess 22, the gases and liquids are unlikely to come into contact with the lower surface of the photodiode 30. The photodiode 30 is unlikely to be etched from the lower surface, and peeling and the like can be prevented.

[0059] The waveguide 20 has a tapered portion 21 corresponding to the tapered protrusion 50. Because the protrusion 50 is joined to the tapered portion 21, the protrusion 50 is less likely to be etched by the etchant in the recess 22. When the shape of the protrusion 50 is changed as shown in FIGS. 5A to 5D , the waveguide 20 only needs to have a shape corresponding to the protrusion 50.

[0060] Each of the waveguide 20, the protrusion 50, and the mesa 54 has a tapered portion. Since the light-receiving element 300 has a three-step tapered structure, it is possible to reduce the loss of light.

[0061] The mesa 54 may be a rectangular parallelepiped as in the first embodiment, and the photodiode 30 may be bonded to the slab portion 26 and not exposed in the recess 22 as in the third embodiment.

[0062] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present disclosure as described in the claims. [Explanation of symbols]

[0063] 10, 12 board 11. Insulating film 14 Box Layer 16 Silicon Layer 20 Waveguide 21, 55, 56 Tapered section 22 recess 24 Terrace 26, 52 Slab section 30 Photodiode 32, 36 Semiconductor layer 34 Light absorption layer 38 Contact layer 40, 42 electrodes 44, 46 pads 50 Protrusion 53 parts 54 Mesa 100, 200, 300 light receiving element

Claims

1. a substrate having a silicon layer; a photodiode formed of a III-V compound semiconductor and bonded to the silicon layer; the silicon layer has a waveguide; the photodiode includes a first semiconductor layer, a light absorption layer, and a second semiconductor layer; the first semiconductor layer contacts the silicon layer; the light absorption layer and the second semiconductor layer are stacked in this order on a surface of the first semiconductor layer opposite to the silicon layer, the first semiconductor layer has a first conductivity type; the second semiconductor layer has a second conductivity type; the first semiconductor layer has a protruding portion and a first slab portion; The protruding portion is connected to the first slab portion, and the light receiving element protrudes from the first slab portion to a position overlapping with the waveguide.

2. the protrusion has a first tapered portion; The light-receiving element according to claim 1 , wherein the first tapered portion has a shape tapered along an extension direction of the waveguide.

3. 3. The light-receiving element according to claim 1, wherein the length of the protrusion is 2 [mu]m or more.

4. 3. The light-receiving element according to claim 1, wherein the tip of the protrusion has a curved surface.

5. the photodiode has a mesa; 3. The light-receiving element according to claim 1, wherein the mesa includes the light absorption layer and the second semiconductor layer, is located on the first slab portion, and faces the protrusion in the extension direction of the waveguide.

6. the mesa has a second tapered portion; The light-receiving element according to claim 5 , wherein the second tapered portion has a shape tapered along an extension direction of the waveguide.

7. 7. The light-receiving element according to claim 6, wherein the length of the second tapered portion is 5 [mu]m or more.

8. the silicon layer has a recess and a second slab portion; the recessed portions are recessed from the second slab portion and are located on both sides of the waveguide; the waveguide is connected to an end of the second slab portion; 6. The light-receiving element according to claim 5, wherein the first slab portion of the photodiode is joined to the second slab portion.

9. The second slab portion protrudes outward from the first slab portion, 9. The light-receiving element according to claim 8, wherein the waveguide protrudes outward from the protrusion.

10. bonding a photodiode formed of a III-V compound semiconductor to the silicon layer of the substrate; forming a slab portion and a protrusion portion on the photodiode; the silicon layer has a waveguide; the photodiode includes a first semiconductor layer, a light absorption layer, and a second semiconductor layer; the first semiconductor layer contacts the silicon layer; the light absorption layer and the second semiconductor layer are stacked in this order on a surface of the first semiconductor layer opposite to the silicon layer, the first semiconductor layer has a first conductivity type; the second semiconductor layer has a second conductivity type; the first semiconductor layer has the protruding portion and the slab portion, The protrusion is connected to the slab and protrudes from the slab to a position overlapping the waveguide.

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