Light receiving element and method for manufacturing light receiving element

Abstract

The invention provides a light-receiving element and a method for manufacturing the light-receiving element. The light-receiving element has high light-receiving sensitivity and is not easy to damage. A light-receiving element is provided with: a substrate having a silicon layer; and a photodiode formed of a Group III-V compound semiconductor and bonded to the silicon layer, the silicon layer including a waveguide, a recess, a void, and a wall provided between the recess and the void, the waveguide being connected to the wall, the waveguide and the recess being provided outside the photodiode, and the photodiode being formed of a Group III-V compound semiconductor. The void is provided at a position overlapping the photodiode.

Description

Technical Field

[0001] This invention relates to a light-receiving element and a method for manufacturing a light-receiving element. Background Technology

[0002] By bonding a photodiode formed from a III-V compound semiconductor to a substrate such as an SOI (Silicon On Insulator) substrate (silicon photonics) with a waveguide formed thereon, a hybrid light-receiving element can be formed (e.g., non-patent document 1).

[0003] Existing technical documents Non-patent literature Non-patent document 1: Ye Wang, et al. "High-Power Photodiodes With 65 GHzBandwidth 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 The problem that the invention aims to solve To expand the operating bandwidth, photodiodes can be miniaturized. To achieve high light sensitivity even in a small photodiode, the coupling efficiency to the photodiode needs to be improved. By designing the portion of the substrate overlapping the photodiode as an air-cladding structure, the light-to-photodiode containment can be enhanced, thus improving light sensitivity. However, there is a risk that liquid chemicals may penetrate the air cladding and damage the photodiode. Therefore, the object of this invention is to provide a light-receiving element with high light sensitivity and low risk of damage, as well as a method for manufacturing the light-receiving element.

[0004] means for solving problems The light-receiving element of the present invention 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 comprising a waveguide, a recess, a gap, and a wall, the wall being disposed between the recess and the gap, the waveguide being connected to the wall, the waveguide and the recess being disposed outside the photodiode, and the gap being disposed at a position overlapping with the photodiode.

[0005] Invention Effects According to the present invention, a light-receiving element with high light sensitivity and low risk of damage, as well as a method for manufacturing the light-receiving element, can be provided. Attached Figure Description

[0006] Figure 1A This is a top view illustrating the light-receiving element according to the first embodiment.

[0007] Figure 1B This is a three-dimensional diagram illustrating a light-receiving element.

[0008] Figure 2A This is an example of a cross-sectional view of a light-receiving element.

[0009] Figure 2B This is an example of a cross-sectional view of a light-receiving element.

[0010] Figure 3A This is a top view illustrating the parameters in the simulation.

[0011] Figure 3B This is a mapping diagram illustrating the simulation results.

[0012] Figure 3C This is a mapping diagram illustrating the simulation results.

[0013] Figure 4A This is a top view illustrating an example of a method for manufacturing a light-receiving element.

[0014] Figure 4B This is a perspective view illustrating an example of a method for manufacturing a light-receiving element.

[0015] Figure 5A This is a top view illustrating an example of a method for manufacturing a light-receiving element.

[0016] Figure 5B This is a perspective view illustrating an example of a method for manufacturing a light-receiving element.

[0017] Figure 6A This is a top view illustrating an example of a method for manufacturing a light-receiving element.

[0018] Figure 6B This is a perspective view illustrating an example of a method for manufacturing a light-receiving element.

[0019] Figure 7A This is a top view illustrating an example of a method for manufacturing a light-receiving element.

[0020] Figure 7B This is a perspective view illustrating an example of a method for manufacturing a light-receiving element.

[0021] Figure 8A This is a top view illustrating an example of a method for manufacturing a light-receiving element.

[0022] Figure 8B This is a perspective view illustrating an example of a method for manufacturing a light-receiving element.

[0023] Figure 9 This is a top view illustrating the light-receiving element according to the second embodiment.

[0024] Figure 10A This is a top view illustrating the light-receiving element according to the third embodiment.

[0025] Figure 10B This is a diagram illustrating light sensitivity.

[0026] Figure 11A This is a perspective view illustrating the light-receiving element according to the fourth embodiment.

[0027] Figure 11B This is a three-dimensional view illustrating the substrate.

[0028] Figure 12 The graph illustrates the calculated results of light sensitivity and quantum efficiency.

[0029] Figure 13A This is a top view illustrating the parameters in the simulation.

[0030] Figure 13B This is a mapping diagram illustrating the simulation results.

[0031] Figure 13C This is a mapping diagram illustrating the simulation results.

[0032] Figure 14A This is a mapping diagram illustrating the simulation results.

[0033] Figure 14B This is a mapping diagram illustrating the simulation results.

[0034] Explanation of reference numerals in the attached figures 10, 12: Substrate; 11: Insulating film; 14: Buried oxide layer; 16: Silicon layer; 20, 26: Waveguide; 21, 25, 45, 29: Taper; 22: Recess; 24: Wall; 27: Void; 28, 40: Slatted section; 30: Photodiode; 32, 36: Semiconductor layer; 34: Light absorption layer; 38: Contact layer; 42: Protrusion; 44: Mesa; 46: Migration structure; 47: Linear section; 50, 52: Electrode; 54, 56: Pad; 100, 200, 300, 400: Light receiving element. Detailed Implementation

[0035] One aspect of the present invention is (1) a light-receiving element, wherein the light-receiving element 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 comprising a waveguide, a recess, a gap, and a wall, the wall being disposed between the recess and the gap, the waveguide being connected to the wall, the waveguide and the recess being disposed outside the photodiode, and the gap being disposed at a position overlapping with the photodiode. Since the gap functions as an air cladding, light can be effectively contained within the photodiode, improving light sensitivity. By miniaturizing the photodiode, high-speed operation is possible. The wall, located between the recess and the gap, blocks liquids such as chemicals. Since etchants do not enter the gap, damage to the photodiode is less likely.

[0036] (2) Alternatively, based on (1) above, the silicon layer includes a first cone portion, the width of which is larger closer to the photodiode and smaller further away from the photodiode, and the waveguide is connected to the first cone portion. This can reduce light loss and improve light sensitivity.

[0037] (3) Alternatively, based on (2) above, the first cone is located between the wall and the waveguide, and is connected to both the wall and the waveguide. This can reduce light loss and improve light sensitivity.

[0038] (4) Alternatively, based on any one of (1) to (3) above, the silicon layer has a second cone portion, which is connected to the wall and overlaps with the photodiode. The width of the second cone portion is larger closer to the wall and smaller further away from the wall. This can reduce light loss and improve light sensitivity.

[0039] (5) Alternatively, based on (2) above, the wall may include the first conical portion. This can reduce light loss and improve light sensitivity.

[0040] (6) Alternatively, based on any one of (1) to (5) above, the silicon layer has a first slat portion, the photodiode is bonded to the first slat portion, the wall is connected to the first slat portion, and the gap is surrounded by the wall and the first slat portion. Since liquids and the like will not penetrate the gap, the photodiode is less likely to be damaged.

[0041] (7) Alternatively, based on any one of (1) to (6) above, the photodiode includes a first semiconductor layer, a light-absorbing layer, and a second semiconductor layer. The first semiconductor layer has a first conductivity type, and the second semiconductor layer has a second conductivity type. The first semiconductor layer is bonded to the silicon layer. The light-absorbing layer and the second semiconductor layer are sequentially stacked on the first semiconductor layer to form a mesa. The gap is disposed at a position overlapping the mesa. Since the gap functions as an air cladding, it can confine the light within the mesa. By enabling efficient coupling of light with the light-absorbing layer, the light sensitivity can be improved.

[0042] (8) Alternatively, based on (7) above, the first semiconductor layer includes a second slat portion and a protrusion, the protrusion being connected to the second slat portion and protruding from the second slat portion toward the waveguide, the mesa protruding from the second slat portion in a direction opposite to the silicon layer, and the gap being disposed at a position overlapping the mesa and the second slat portion. This can improve coupling efficiency and light sensitivity.

[0043] (9) Alternatively, based on (8) above, the platform extends from the position overlapping with the second slat portion to the position overlapping with the protrusion. Light is absorbed by the platform before reaching the wall. This reduces light loss caused by the wall and improves light sensitivity.

[0044] (10) Alternatively, based on any of (7) to (9) above, the platform has a third cone portion, which has a shape that tapers at the front end along the extension direction of the waveguide. This increases the coupling efficiency and further improves the light-receiving sensitivity.

[0045] (11) Alternatively, based on any of (7) to (10) above, a portion of the mesa overlaps with and is supported by the silicon layer. Mechanical strength is improved.

[0046] (12) A method for manufacturing a light-receiving element, the light-receiving element comprising: a substrate having a silicon layer; and a photodiode formed of a III-V compound semiconductor, wherein the silicon layer includes a waveguide, a recess, a gap, and a wall, the wall being disposed between the recess and the gap, the waveguide being connected to the wall, the method for manufacturing the light-receiving element comprising: a step of bonding the photodiode to the silicon layer; and a step of wet etching the photodiode, wherein after the wet etching step, the waveguide and the recess are disposed outside the photodiode, and the gap is disposed at a position overlapping with the photodiode. Since the gap functions as an air cladding, light can be strongly confined within the photodiode. Light-receiving sensitivity can be improved. By miniaturizing the photodiode, high-speed operation is possible. The wall 24 is located between the recess and the gap, blocking liquids such as chemicals. Since the etchant does not enter the gap, damage to the photodiode is less likely.

[0047] [Detailed Description of Embodiments of the Invention] Hereinafter, specific examples of the light-receiving element and the method for manufacturing the light-receiving element according to embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to these examples, but is intended to include all modifications within the meaning and scope equivalent to the claims, as shown in the claims.

[0048] <First Implementation Method> (Light receiving element) Figure 1A This is a top view illustrating the light-receiving element 100 according to the first embodiment. Figure 1B This is a three-dimensional view illustrating the light-receiving element 100. Figure 2A as well as Figure 2B This is a cross-sectional view of the light-receiving element 100 as an example. Figure 2A The diagram illustrates along Figure 1A The cross section of line AA. Figure 2B The diagram illustrates along Figure 1A The cross-section of line BB. Substrate 12 of substrate 10 is omitted in the perspective view.

[0049] like Figure 1A as well as Figure 1B As shown, the light-receiving element 100 is a hybrid type, comprising a substrate 10, a photodiode 30, and a migration structure 46. In the migration structure 46, light migrates from the substrate 10 to the photodiode 30. The photodiode 30 is coupled to the upper surface of the substrate 10, absorbs light, and outputs an electrical signal. 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 orthogonal to both the X-axis and Z-axis directions. One direction along the X-axis is designated as the -X direction, and the other as the +X direction.

[0050] (Substrate) like Figure 2A as well as Figure 2B As shown, substrate 10 is an SOI (Silicon on Insulator) substrate, having substrate 12, buried oxide layer 14, and silicon layer 16. Substrate 12, buried oxide layer 14, and silicon layer 16 are sequentially stacked along the Z-axis. Substrate 12 is formed, for example, of silicon (Si). Buried oxide layer 14 is formed, for example, of silicon oxide (SiO2). The thickness of buried oxide layer 14 is, for example, 3 μm.

[0051] The thickness of silicon layer 16 is, for example, 220 nm. The upper surface of substrate 10 and the surface of photodiode 30 are covered by insulating film 11. Insulating film 11 is formed, for example, from SiO2 with a thickness of 1 μm. The refractive index of silicon layer 16 is 3.45. The refractive index of buried oxide layer 14 and insulating film 11 is lower than that of silicon layer 16, at 1.45. These refractive indices are values ​​for light with a wavelength of 1.55 μm. Waveguides, etc., are provided in silicon layer 16.

[0052] like Figure 1A as well as Figure 1B As shown, the substrate 10 has a waveguide 20, a cone 21 (first cone), a recess 22, a wall 24, a cone 25 (second cone), a waveguide 26, a gap 27, and a slat portion 28 (first slat portion). The slat portion 28 is a planar portion in the silicon layer 16, parallel to the XY plane.

[0053] In the X-axis direction, waveguide 20, cone 21, wall 24, cone 25, and waveguide 26 are arranged in this order. Cone 21 is located between waveguide 20 and wall 24, and is connected to both waveguide 20 and wall 24. The closer to wall 24, the wider cone 21; the farther away from wall 24, the narrower the width of cone 21. Cone 25 is located between wall 24 and waveguide 26, and is connected to both wall 24 and waveguide 26. The closer to wall 24, the wider cone 25; the farther away from wall 24, the narrower the width of cone 25.

[0054] Waveguides 20 and 26 are parallel to the X-axis. Waveguide 20 is connected to the front end of tapered portion 21. Recess 22 is a groove that extends parallel to the X-axis and is located on both sides of waveguide 20 and tapered portion 21 in the Y-axis direction. Waveguide 20 and recess 22 extend from wall 24 to the end of substrate 10 on the -X side in the X-axis direction. The width W1 of waveguide 20 is, for example, 0.3 μm or more and 0.6 μm or less.

[0055] Waveguide 26 is connected to the front end of tapered portion 25. Waveguide 26 does not reach the +X side end of substrate 10, but extends to the middle of substrate 10. Gap 27 is located on both sides of waveguide 26 and tapered portion 25 in the Y-axis direction.

[0056] Wall 24 extends along the Y-axis and is perpendicular to the X-axis. Wall 24 connects to the slat portion 28 and is located between the recess 22 and the gap 27, cutting off the space between the recess 22 and the gap 27. The recess 22 is located on the -X side of wall 24, and the gap 27 is located on the +X side.

[0057] The upper surfaces of waveguide 20, taper 21, wall 24, taper 25, waveguide 26, and slat portion 28 are at the same height in the Z-axis direction, protruding from recess 22 and void 27. Recess 22 and void 27 are recessed in the Z-axis direction than slat portion 28. Recess 22 and void 27 can penetrate the silicon layer 16 or extend to the middle of the silicon layer 16. An insulating film 11 is embedded in the recess 22. Void 27 is a cavity filled with air.

[0058] (Photodiode) Photodiode 30 is a semiconductor device formed from a III-V compound semiconductor. Photodiode 30 is bonded to silicon layer 16. (The text abruptly ends here.) Figure 1B and Figure 2B As shown, the photodiode 30 has a semiconductor layer 32 (first semiconductor layer), a light-absorbing layer 34, a semiconductor layer 36 (second semiconductor layer), and a contact layer 38 (second semiconductor layer). The semiconductor layer 32 is in contact with the silicon layer 16 of the substrate 10. On the surface of the semiconductor layer 32 opposite to the substrate 10, the light-absorbing layer 34, the semiconductor layer 36, and the contact layer 38 are sequentially stacked.

[0059] Semiconductor layer 32 is formed, for example, of n-type (first conductivity type) indium phosphide (n-InP). Semiconductor layer 32 is, for example, doped with silicon (Si). The thickness of semiconductor layer 32 is, for example, 400 nm. Light-absorbing layer 34 is formed, for example, of undoped indium gallium arsenide (InGaAs). Light-absorbing layer 34 may also be formed solely of bulk InGaAs. The thickness of light-absorbing layer 34 is, for example, 400 nm. Semiconductor layer 36 is formed, for example, of p-type (second conductivity type) indium phosphide (p-InP). The thickness of semiconductor layer 36 is, for example, 1300 nm. Contact layer 38 is formed, for example, of p+ type indium gallium arsenide ((p+)-InGaAs). The thickness of contact layer 38 is, for example, 300 nm. Semiconductor layer 36 and contact layer 38 are, for example, doped with zinc (Zn). The semiconductor layer of photodiode 30 may also be formed of other III-V compound semiconductors.

[0060] like Figure 1A as well as Figure 1B As shown, the photodiode 30 includes a slat portion 40 (second slat portion), a protrusion 42, and a mesa 44. As... Figure 1B As shown, the semiconductor layer 32 has a slat portion 40 and a protrusion 42. The mesa 44 includes a light-absorbing layer 34, a semiconductor layer 36, and a contact layer 38. Figure 2A As shown, the protrusion 42 is covered by the insulating film 11. Figure 2B As shown, the slat portion 40 and the table surface 44 are also covered by the insulating film 11.

[0061] like Figure 1A as well as Figure 1B As shown, the slat portion 40 is planar and is disposed in an area larger than the mesa 44, and is joined to the slat portion 28 of the silicon layer 16. The width of the slat portion 40 is greater than the width of the protrusion 42.

[0062] The protrusion 42 is connected to the -X side end of the slat portion 40, protruding from this end to a position overlapping with the tapered portion 21 of the silicon layer 16. The protrusion 42 is entirely tapered, having a shape that tapers at the front end along the X-axis direction. The front end of the protrusion 42 is, for example, curved. The protrusion 42 is, for example, linearly symmetrical in the X-axis direction.

[0063] The closer to the slat portion 40, the wider the protrusion 42; the farther away from the slat portion 40, the narrower the width of the protrusion 42. The width W2 of the portion of the protrusion 42 that connects to the slat portion 40 is, for example, 1 μm or more and 10 μm or less. The length L1 of the protrusion 42 in the X-axis direction is, for example, 2 μm or more and 100 μm or less.

[0064] The platform 44 is located above the slat portion 40, protrudes from the slat portion 40 in the Z-axis direction, and is opposite to the protrusion 42 in the X-axis direction. The shape of the platform 44 is, for example, a cuboid. Figure 1B The length L2 of the platform 44 in the X-axis direction is, for example, 5 μm or more and 20 μm or less. The width W3 of the platform 44 in the Y-axis direction is, for example, 0.5 μm or more and 6 μm or less, and 2 μm as an example. The distance D1 from the front end of the platform 44 on the -X side to the front end of the slat portion 40 on the -X side is, for example, 20 μm or less.

[0065] The tapered portion 21 of silicon layer 16 overlaps with the protrusion 42 of photodiode 30 in the Z-axis direction. Wall 24 and tapered portion 25 overlap with slat portion 40. Waveguide 26 and gap 27 overlap with slat portion 40 and mesa 44. Waveguide 26 extends to the +X side end of mesa 44. The closer to mesa 44 of photodiode 30, the wider the tapered portion 21; the farther away from mesa 44, the narrower the width of the tapered portion 21.

[0066] The migration structure 46 includes a cone 21 and a cone 25 of the silicon layer 16, and a protrusion 42 of the photodiode 30. The migration structure 46 is kite-shaped when viewed from above.

[0067] like Figure 1AAs shown, the light-receiving element 100 has electrodes 50 and 52, pads 54 and 56. The electrodes and pads are formed of metal. The two electrodes 50 are cathodes and are electrically connected to the semiconductor layer 32. Pad 54 is electrically connected to the electrodes 50. Electrode 52 is an anode and is electrically connected to the contact layer 38. Pad 56 is electrically connected to the electrodes 52.

[0068] The length L3 of pad 54 in the X-axis direction is, for example, 50 μm or more and 150 μm or less. The width W4 of pad 54 in the Y-axis direction is, for example, 50 μm or more and 100 μm or less. The size of pad 56 is, for example, the same as that of pad 54. The center-to-center distance D2 between pad 54 and pad 56 is, for example, 100 μm or more and 200 μm or less.

[0069] The light-receiving element 100 detects light incident on the substrate 10. The wavelength of the light being detected is, for example, 1.55 μm, or it can be above 1.26 μm and below 1.63 μm. The light-receiving element 100 is used to receive high-speed modulated optical signals in an optical communication system. The substrate 10 and the photodiode 30 are evanescently coupled. A pin (positive-intrinsic-negative) junction is formed on the mesa 44 of the photodiode 30 through an n-type semiconductor layer 32, a light-absorbing layer 34, and a p-type semiconductor layer 36. A reverse bias voltage is applied to the photodiode 30 using pads 54 and 56. By applying the voltage, the mesa 44 is depleted.

[0070] Light propagates in waveguide 20 and migrates from waveguide 20 to photodiode 30 in migration structure 46. The light-absorbing layer 34 of photodiode 30 absorbs the light, generating photocarriers (electron-hole pairs). These photocarriers are output as photocurrent.

[0071] The migration structure 46 has a cone portion 21 and a cone portion 25, and a protrusion 42 of a photodiode 30. This reduces light reflection and scattering, thus minimizing light loss.

[0072] The gap 27 of the silicon layer 16 is surrounded by the wall 24 and the slat portion 28 in the XY plane, and is covered by the slat portion 40 of the photodiode 30 in the Z-axis direction. The gap 27 is sealed by the wall 24, the slat portion 28, and the slat portion 40. By making the gap 27 function as an air cladding, the sealing of light to the light absorption layer 34 of the photodiode 30 can be enhanced. By enabling light to couple to the light absorption layer 34 with high efficiency, the light sensitivity is increased.

[0073] (simulation) Figure 3AThis is a top view illustrating the parameters in the simulation, with the migration structure 46 magnified. The width W1 of waveguide 20 and the width W5 of waveguide 26 are set to 0.5 μm. The thickness T1 of wall 24 in the X-axis direction is set to 1 μm. The length L4 of the cone 21 of silicon layer 16 is set to 60 μm. The length L5 of cone 25 is set to 9 μm. The width W6 of the front end of protrusion 42 of photodiode 30 is set to 0.2 μm. The width of the portion of protrusion 42 that connects to slat 40 is set to W2. The distance from the end of protrusion 42 in the Y-axis direction to the end of cone 21 is set to D3. By changing the width W2 and the distance D3, the transmittance of light from the -X side to the +X side of wall 24 is calculated.

[0074] Figure 3B as well as Figure 3C This is a mapping diagram illustrating the simulation results. The horizontal axis represents the width W2. The vertical axis represents the distance D3. The width W2 is varied from 1.0 μm to 5.0 μm in 0.5 μm increments. The distance D3 is varied from 0.0 μm to 0.5 μm in 0.1 μm increments. In the mapping diagram, the areas with higher density of diagonal lines have higher transmittance.

[0075] Figure 3B This represents the transmittance in mode 0. If the width W2 of the protrusion 42 is large and the distance D3 is large, the transmittance decreases. With a width W2 of 5.0 μm and a distance D3 of 0.5 μm, the transmittance is 55%. If the width W2 of the protrusion 42 is small and the distance D3 is small, the transmittance increases. With a width W2 of 1.0 μm and a distance D3 of 0.1 μm, the transmittance is 96%.

[0076] Figure 3C This represents the total transmittance (Total) of light combining the 0th and higher-order modes. Regardless of the width W2 or distance D3, the transmittance is 90% or higher. For distances of D3 of 0.0 μm, 0.1 μm, or 0.5 μm, the transmittance is 99% regardless of the width W2. For a distance of D3 of 0.2 μm and widths W2 of 1.0 μm, 2.0 μm to 3.0 μm, or 4.0 μm to 5.0 μm, the transmittance is 99%. For a distance of D3 of 0.3 μm and widths W2 of 1.5 μm, 3.0 μm to 5.0 μm, the transmittance is 99%. For a distance of D3 of 0.4 μm and widths W2 of 1.0 μm, 2.0 μm, 3.5 μm, 4.0 μm, or 5.0 μm, the transmittance is 99%. For other combinations of distance D3 and width W2, the transmittance is 97%. The zero-order mode and higher-order modes are absorbed by the photodiode 30 through the migration structure 46, thereby increasing the light sensitivity.

[0077] (Manufacturing method) Figure 4A , Figure 5A , Figure 6A , Figure 7A as well as Figure 8A This is a top view illustrating an example of the manufacturing method of the light-receiving element 100. Figure 4B , Figure 5B , Figure 6B , Figure 7B as well as Figure 8B This is a perspective view illustrating an example of a manufacturing method for the light-receiving element 100.

[0078] like Figure 4A as well as Figure 4B As shown, the silicon layer 16 of substrate 10 (SOI substrate) is subjected to, for example, dry etching. The portion exposed by a mask (not shown) is etched to form recesses 22 and voids 27. The portion covered by the mask (not shown) is not etched. Waveguide 20, taper 21, wall 24, taper 25, waveguide 26, and slat portion 28 are formed in the unetched portion. After dry etching, the mask is removed.

[0079] On an InP substrate different from the substrate 10, a contact layer 38, a semiconductor layer 36, a light-absorbing layer 34, and a semiconductor layer 32 are sequentially epitaxially grown using metal-organic chemical vapor deposition (MOCVD). The InP substrate is then diced to form a photodiode 30. The photodiode 30 immediately after dicing is cuboid and lacks the protrusions 42 and mesas 44.

[0080] like Figure 5A as well as Figure 5B As shown, a photodiode 30 is bonded to the upper surface of substrate 10. During the bonding process, plasma is irradiated onto one side of silicon layer 16 and the side of semiconductor layer 32 of photodiode 30 to activate these sides. The side of semiconductor layer 32 is brought into contact with the side of silicon layer 16, bonding photodiode 30 to silicon layer 16. Photodiode 30 covers the upper surface of silicon layer 16. Taper 21, wall 24, taper 25, waveguide 26, and gap 27 are located below photodiode 30.

[0081] After bonding, wet etching is performed to remove the InP substrate from the photodiode 30. Residue remains from the contact layer 38 to the semiconductor layer 32. A chemical solution is used in the wet etching. The solution enters the recess 22 but is blocked by the wall 24, making it difficult to penetrate the gap 27. The photodiode 30 is not easily etched from the bonding interface side, preventing damage.

[0082] like Figure 6A as well as Figure 6BAs shown, a mesa 44 is formed on the photodiode 30. The portions of the contact layer 38, semiconductor layer 36, and light-absorbing layer 34 exposed by a mask (not shown) are removed by dry etching. The mesa 44 is formed in the portion covered by the mask. A chlorine-based etching gas is used, for example, in the dry etching. After dry etching, the mask is removed. The semiconductor layer 32 of the photodiode 30 covers the upper surface of the substrate 10.

[0083] like Figure 7A as well as Figure 7B As shown, a slat portion 40 and a protrusion 42 are formed on the photodiode 30. A mask (not shown) covers the mesa 44 and a portion of the semiconductor layer 32. The portion of the semiconductor layer 32 exposed from the mask is removed by wet etching to form the slat portion 40 and the protrusion 42. In the wet etching, for example, a hydrochloric acid-based etchant is used. After the wet etching, the mask is removed. To remove the mask, a buffered hydrofluoric acid solution is used. The void 27 is sealed by the wall 24, the slat portion 28, and the slat portion 40. Therefore, liquids such as etchants are difficult to penetrate the void 27. The photodiode 30 is not easily etched from the bonding interface side.

[0084] like Figure 8A as well as Figure 8B As shown, electrodes 50 and 52, and pads 54 and 56 are formed by vacuum evaporation and stripping. The light-receiving element 100 is formed by dividing the substrate 10.

[0085] According to the first embodiment, the silicon layer 16 of the substrate 10 has a waveguide 20, a tapered portion 21, a recessed portion 22, a wall 24, a tapered portion 25, a waveguide 26, a gap 27, and a slatted portion 28. A photodiode 30 is bonded to the silicon layer 16. The gap 27 functions as an air cladding, strongly confining light within the photodiode 30. By strengthening the light confinement, even with miniaturization of the photodiode 30, light sensitivity can be improved. Miniaturization of the photodiode 30 reduces parasitic capacitance, enabling high-speed operation. Both high sensitivity and wide bandwidth can be achieved.

[0086] The wall 24 of the silicon layer 16 is disposed between the recess 22 and the gap 27. The gap 27 is sealed by the wall 24, the slat portion 28, and the photodiode 30. The wet etching solution is blocked by the wall 24, making it difficult for it to penetrate the gap 27. The photodiode 30 is not etched from the bonding interface side, and is less prone to damage. Liquids used in cleaning are also difficult to enter the gap 27. It also prevents damage to the photodiode 30 caused by the vaporization of liquids.

[0087] The gap 27 is surrounded by the wall 24 and the slat portion 28, and is covered by the slat portion 40 of the photodiode 30. This prevents liquid from entering from all directions. It effectively prevents damage to the photodiode 30. It also prevents liquid intrusion during wet etching processes such as those used to fabricate the protrusion 42, other wet etching processes, and processes involving the use of liquids.

[0088] The migration structure 46 includes a tapered portion 21 of the silicon layer 16. The wall 24 is perpendicular to the X-axis, which is the direction of light propagation, thus easily reflecting light. Since the tapered portion 21 is located between the waveguide 20 and the wall 24, light gradually migrates within the tapered portion 21 to the photodiode 30. This prevents light reflection and scattering, reducing light loss. Because the low-loss light is transferred to the photodiode 30, the light sensitivity is increased.

[0089] A tapered portion 25 is provided between the wall 24 of the silicon layer 16 and the waveguide 26. The cross-sectional shapes of the tapered portion 21 and the tapered portion 25 gradually change, which can reduce light loss.

[0090] The mesa 44 of the photodiode 30 includes a light-absorbing layer 34, a semiconductor layer 36, and a contact layer 38. In the Z-axis direction, the gap 27 overlaps with the mesa 44. By allowing the gap 27 to function as an air cladding, light is strongly confined within the mesa 44 and efficiently coupled to the light-absorbing layer 34. This improves light sensitivity.

[0091] The semiconductor layer 32 of the photodiode 30 has a slat portion 40 and a protrusion 42. The slat portion 40 is bonded to the silicon layer 16. The protrusion 42 protrudes from the slat portion 40 toward the waveguide 20 and overlaps with the tapered portion 21. The protrusion 42, the tapered portion 21, and the tapered portion 25 form a migration structure 46. Light propagating in the waveguide 20 is transferred to the photodiode 30 in the migration structure 46. By improving the coupling efficiency, light can be confined in the light-absorbing layer 34, thereby improving the light-receiving sensitivity.

[0092] The protrusion 42 of the photodiode 30 can also have a tapered shape. The width of the tapered portion 21 and the protrusion 42 widens towards the photodiode 30. Single-mode light propagates in the waveguide 20, and higher-order modes are excited in the tapered portion 21 and the protrusion 42, extending over a wider range. Since there is no localized light intensity, there is also no localized photocarrier. High responsivity can also be obtained for high-frequency optical signals.

[0093] like Figures 3A to 3C As shown, by adjusting the size, the transmittance of both the zero-order mode and higher-order modes can be increased to over 90%. The photodiode 30 absorbs both the zero-order and higher-order modes after transmission.

[0094] The central portion of the mesa 44 of the photodiode 30 in the Y-axis direction overlaps with and is supported by the waveguide 26 of the silicon layer 16. This improves the mechanical strength of the light-receiving element 100. Gaps 27 are provided on both sides of the waveguide 26, overlapping with the mesa 44. Gaps 27 function as an air cladding, thus improving light-receiving sensitivity. Alternatively, the tapered portion 21 and 25, and the waveguide 26, may not be provided in the silicon layer 16. The protrusion 42 may also not be provided in the photodiode 30.

[0095] <Second Implementation Method> Figure 9 This is a top view illustrating the light-receiving element 200 according to the second embodiment. Descriptions of configurations identical to those in the first embodiment are omitted. The mesa 44 has a cone 45 (third cone). The cone 45 is located at the -X side front end of the mesa 44. The closer to the waveguide 20, the smaller the width of the cone 45; the farther away from the waveguide 20, the larger the width of the cone 45.

[0096] According to the second embodiment, the gap 27 functions as an air cladding, thus effectively confining light within the photodiode 30. The mesa 44 has a tapered portion 45, thereby increasing coupling efficiency and further reducing light loss. The wall 24 can block the liquid. Since the liquid is difficult to enter the gap 27, etching of the bonding interface side of the photodiode 30 can be prevented.

[0097] <Third Implementation Method> Figure 10A This is a top view illustrating the light-receiving element 300 according to the third embodiment, with an enlarged view of the portion including the platform 44. Descriptions of configurations identical to those in the first or second embodiments are omitted.

[0098] like Figure 10A As shown, the migration structure 46 is kite-shaped. The width of the tapered portion 21 of the silicon layer 16 gradually increases towards the slatted portion 40 of the photodiode 30. In other words, the tilt angle of the tapered portion 21 relative to the X-axis gradually increases. The recess 22 is tilted relative to the X-axis in a corresponding manner to the tapered portion 21. Figure 10A In the diagram, dotted lines indicate the locations where the angle of the cone 21 changes.

[0099] The silicon layer 16 has a cone 25 and a gap 27 on the +X side relative to the wall 24, but no waveguide 26. When viewed from above, the gap 27 is Y-shaped. The gap 27 is located on both sides of the cone 25 and has a straight line shape parallel to the X-axis on the +X side relative to the cone 25.

[0100] A tapered portion 45 is provided at the front end of the mesa 44 on the -X side of the photodiode 30. A straight portion 47 is defined in the mesa 44 on the +X side, beyond the tapered portion 45. The straight portion 47 is parallel to the X-axis direction. The mesa 44 protrudes above the protrusion 42 from its position overlapping with the slat portion 40. The tapered portion 45 of the mesa 44 is located above the tapered portion 21 of the silicon layer 16 and the protrusion 42 of the photodiode 30. The portion of the straight portion 47 of the mesa 44 connected to the tapered portion 45 is located above the tapered portion 21 and the protrusion 42. The straight portion 47 extends from the protrusion 42 above the slat portion 40 and the gap 27. The mesa 44 is supported by the tapered portions 21 and 25 of the silicon layer 16 and is supported by the portion of the slat portion 28 that connects to the gap 27.

[0101] Set the -X side front end of the platform 44 to position X1. Set the midpoint of the cone 25 in the platform 44 to position X2. Set the +X side front end of the platform 44 to position X3.

[0102] Figure 10B This is a diagram illustrating the light-receiving sensitivity. The horizontal axis represents the position of the platform 44 in the X-axis direction. The left direction on the horizontal axis is the -X direction, and the right direction is the +X direction. The vertical axis represents the light-receiving sensitivity. The solid line represents the third embodiment. The dashed line represents Comparative Example 1. In Comparative Example 1, the silicon layer 16 does not have the wall 24 or the void 27. The slat portion 28 of the silicon layer 16 is disposed below the photodiode 30. Other configurations are the same as in the third embodiment.

[0103] Light propagates from the -X side to the +X side into waveguide 20, migrates to photodiode 30, and is absorbed by light absorption layer 34. The light-receiving sensitivity increases from the -X side towards the +X side. The light-receiving sensitivity is lowest at position X1 at the front end of the -X side of the platform 44. From position X1 to position X2, the light-receiving sensitivity of the third embodiment is the same as that of Comparative Example 1. As the light-receiving sensitivity moves from position X2 to position X3, the difference between the light-receiving sensitivity of the third embodiment and that of Comparative Example 1 increases. In Comparative Example 1, since no air cladding is provided, the light containment is weak, and light loss in the slat portion 28 increases. The light-receiving sensitivity decreases.

[0104] According to the third embodiment, the mesa 44 of the photodiode 30 protrudes above the protrusion 42 and extends towards the -X side relative to the wall 24. Since the mesa 44 protrudes beyond the wall 24, light is transferred to the mesa 44 and absorbed before light loss due to the wall 24 occurs. The effect of the wall 24 on light absorption is reduced. A gap 27 is provided at a position towards the +X side relative to the wall 24, confining the light within the mesa 44. By enabling the light-absorbing layer 34 to absorb light efficiently, the light sensitivity is increased.

[0105] like Figure 10AAs shown, the straight portion 47 of the platform 44 is located above the slat portion 28 and is supported by the slat portion 28. Mechanical strength is improved.

[0106] <Fourth Implementation Method> Figure 11A This is a perspective view illustrating the light-receiving element 400 according to the fourth embodiment. Figure 11B This is a perspective view illustrating substrate 10. Descriptions of configurations identical to any of the first to third embodiments are omitted. Although the illustrations are omitted, the light-receiving element 400 has the same... Figure 1A The same electrodes. Migration structure 46 is of the Dart type.

[0107] like Figure 11A as well as Figure 11B As shown, the wall 24 of the silicon layer 16 has a conical shape, for example, the entire wall 24 is a cone 29 (first cone). The width of the cone 29 is narrower as it moves away from the photodiode 30 and wider as it moves closer to the photodiode 30. The cone 29 is connected to the slat portion 28. A waveguide 20 is connected to the front end of the cone 29. The waveguide 26 is connected to the inner wall of the cone 29. Gaps 27 are provided on both sides of the waveguide 26. The protrusion 42 of the photodiode 30 overlaps with the cone 29.

[0108] Figure 12 This is a graph illustrating the calculated results of light-receiving sensitivity and quantum efficiency. The left vertical axis represents light-receiving sensitivity. The right vertical axis represents quantum efficiency. The horizontal axis represents the length of the mesa 44 along the X-axis. The length range is set to 0 μm to 100 μm. The length of the cone 45 of the mesa 44 is 10 μm. When the length of the mesa 44 is 10 μm or more, a straight section 47 is connected to the +X side of the 10 μm long cone 45. The width W3 of the mesa 44 is set to 2 μm. Figure 12 In the dashed line, the length of mesa 44 is between 30 μm and 40 μm, and the area of ​​the upper surface of mesa 44 is 54 μm². 2 With a platform length of 60 μm, the area is 72 μm. 2 To achieve a 3dB bandwidth of 60GHz, the area should be, for example, 54μm. 2 That's all.

[0109] exist Figure 12In the diagram, the solid line represents the fourth embodiment. The dotted line represents Comparative Example 2. Comparative Example 2 does not have the wall 24 and the void 27. Other configurations are the same as in the fourth embodiment. The longer the mesa 44, the higher the light-receiving sensitivity and quantum efficiency. The light-receiving sensitivity and quantum efficiency of the fourth embodiment are higher than those of Comparative Example 2. Within the length shown by the dotted line, Comparative Example 2 has a light-receiving sensitivity of approximately 0.7 A / W and a quantum efficiency of approximately 60%. The fourth embodiment has a light-receiving sensitivity of 1.0 A / W and a quantum efficiency of 80%. In Comparative Example 2, to achieve a light-receiving sensitivity of 1.0 A / W and a quantum efficiency of 80%, the length of the mesa 44 is set to 60 μm. However, the area of ​​the mesa 44 becomes 72 μm. 2 Therefore, the capacity increases, making high-speed operation difficult. In the fourth embodiment, with a light sensitivity of 1.0 A / W and a quantum efficiency of 80%, the area of ​​the mesa 44 is 54 μm. 2 Because of the reduced capacity, high-speed operation is possible. That is, it can balance high light sensitivity and high-speed operation.

[0110] (simulation) Figure 13A This is a top view illustrating the parameters in the simulation, with the migration structure 46 magnified. The width W1 of the waveguide 20, the thickness T2 of the wall 24 in the Y-axis direction, and the length L1 of the protrusion 42 of the photodiode 30 are used as parameters.

[0111] Figure 13B as well as Figure 13C This is a mapping diagram illustrating the simulation results. The horizontal axis represents length L1. The vertical axis represents width W1 and thickness T2. Figure 13B as well as Figure 13C In the example, the length L1 is varied from 60 μm to 200 μm in 20 μm increments. The width W1 is varied from 0.4 μm to 2.0 μm in 0.2 μm increments. The thickness T2 of wall 24 varies in the same way as the width W1 of waveguide 20, and is set to a value equal to the width W1. Figure 13B as well as Figure 13C In the middle, the part with high transmittance is surrounded by a dashed line.

[0112] Figure 13BThis represents the transmittance in the zero-mode. With a width W1 and thickness T2 of 0.4 μm, the transmittance is above 90%, for example, reaching 92%, regardless of the length L1. If the width W1 and thickness T2 are greater than 0.4 μm and the length L1 is varied, the transmittance improves periodically. For example, with a width W1 and thickness T2 of 1.8 μm and a length L1 of 120 μm, the transmittance is 88%. With a width W1 and thickness T2 of 2.0 μm and a length L1 of 100 μm or 180 μm, the transmittance increases. With a width W1 and thickness T2 of 1.2 μm to 1.4 μm and a length L1 of 60 μm, the transmittance also increases.

[0113] Figure 13C This represents the transmittance of light combining the 0th and higher order modes. Transmittance increases when the width W1 and thickness T2 are less than 1.2 μm and the length L1 is less than 120 μm. With a width W1, thickness T2 of 120 μm and length L1 of 60 μm, the transmittance is 99%.

[0114] Figure 14A as well as Figure 14B This is a mapping diagram illustrating the simulation results. Figure 14A as well as Figure 14B In the example, the thickness T2 of wall 24 is fixed at 1 μm.

[0115] Figure 14A This represents the transmittance of the 0th mode. Figure 14B This represents the transmittance of light when the zero-order mode and higher-order modes are combined. Figure 14A as well as Figure 14B In the case where the width W1 of waveguide 20 is narrower, the transmittance is higher when the width W1 is wider. Compared to waveguide 20, if the wall 24 is relatively thicker, the light loss increases. Compared to waveguide 20, the thinner the wall 24, the smaller the loss and the higher the transmittance. Figure 14A In the example, with a width W1 of 1.4 μm and a length L1 of 100 μm, the transmittance is 85%. The transmittance is high when the width W1 is greater than 0.8 μm and the length L1 is greater than 180 μm. Figure 14B In the example, if the width W1 is 1.4 μm, the transmittance is above 90% regardless of the length L1.

[0116] According to the fourth embodiment, the gap 27 functions as an air cladding, thus effectively confining light within the photodiode 30. The wall 24 is tapered, thereby reducing light loss and improving light sensitivity. The wall 24 also blocks liquid medication. Since liquid medication has difficulty entering the gap 27, etching at the junction interface of the photodiode 30 is prevented.

[0117] The embodiments of the present invention have been described in detail above, but the present invention is not limited to this specific embodiment. Various modifications and alterations can be made within the scope of the spirit of the present invention as described in the claims.

Claims

1. A light-receiving element, wherein, The light-receiving element comprises: Substrate, having a silicon layer; and A photodiode, formed of a III-V compound semiconductor, is bonded to the silicon layer. The silicon layer includes waveguides, recesses, voids, and walls. The wall is disposed between the recess and the gap. The waveguide is connected to the wall. The waveguide and the recess are disposed outside the photodiode. The gap is positioned at a location overlapping the photodiode.

2. The light-receiving element according to claim 1, wherein, The silicon layer includes a first cone portion. The width of the first cone is larger as it gets closer to the photodiode and smaller as it gets further away from the photodiode. The waveguide is connected to the first cone portion.

3. The light-receiving element according to claim 2, wherein, The first cone is located between the wall and the waveguide, and is connected to both the wall and the waveguide.

4. The light-receiving element according to claim 3, wherein, The silicon layer has a second cone portion. The second cone portion connects to the wall and overlaps with the photodiode. The width of the second cone is larger as it gets closer to the wall and smaller as it gets further away from the wall.

5. The light-receiving element according to claim 2, wherein, The wall includes the first cone portion.

6. The light-receiving element according to claim 1 or 2, wherein, The silicon layer has a first slat portion. The photodiode is coupled to the first slat portion. The wall is connected to the first slat portion. The gap is surrounded by the wall and the first slat portion.

7. The light-receiving element according to claim 1 or 2, wherein, The photodiode comprises a first semiconductor layer, a light-absorbing layer, and a second semiconductor layer. The first semiconductor layer has a first conductivity type. The second semiconductor layer has a second conductivity type. The first semiconductor layer is bonded to the silicon layer. The light-absorbing layer and the second semiconductor layer are sequentially stacked on top of the first semiconductor layer to form a mesa. The gap is positioned at a location that overlaps with the tabletop.

8. The light-receiving element according to claim 7, wherein, The first semiconductor layer includes a second slat portion and a protrusion. The protrusion is connected to the second slat portion and protrudes from the second slat portion toward the waveguide. The mesa protrudes from the second slat portion in a direction opposite to that of the silicon layer. The gap is positioned at a location that overlaps with the tabletop and the second slat portion.

9. The light-receiving element according to claim 8, wherein, The platform extends from the position where it overlaps with the second slat portion to the position where it overlaps with the protrusion.

10. The light-receiving element according to claim 7, wherein, The platform has a third cone-shaped portion. The third cone has a shape that tapers at the front end along the extension direction of the waveguide.

11. The light-receiving element according to claim 7, wherein, A portion of the platform overlaps with and is supported by the silicon layer.

12. A method for manufacturing a light-receiving element, the light-receiving element comprising: a substrate having a silicon layer; and a photodiode formed of a III-V compound semiconductor, wherein, The silicon layer includes waveguides, recesses, voids, and walls. The wall is disposed between the recess and the gap. The waveguide is connected to the wall. The method for manufacturing the light-receiving element includes: The process of bonding the photodiode to the silicon layer; and The process of wet etching the photodiode. After the wet etching process, the waveguide and the recess are disposed outside the photodiode, and the gap is disposed at a position overlapping with the photodiode.

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