Light receiving element and method for manufacturing light receiving element

Abstract

The invention provides a light receiving element capable of reducing light loss and a method for manufacturing the light receiving element. This light-receiving element is provided with: 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 in contact with the silicon layer, a light absorbing layer in contact with the silicon layer, and a second semiconductor layer in contact with the light absorbing layer. The light absorption layer and the second semiconductor layer are laminated on a surface of the first semiconductor layer opposite to the silicon layer in the order of the light absorption layer and the 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 includes a protruding portion and a first plate portion, and the protruding portion is connected to the first plate portion and protrudes from the first plate portion to a position overlapping the waveguide.

Description

Technical Field

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

[0002] By bonding a photodiode made of a III-V compound semiconductor to a substrate such as an SOI (Silicon-On-Insulator) substrate (silicon photonics) that forms a waveguide, a hybrid light-receiving element can be formed (for example, Non-Patent Document 1). The photodiode absorbs light propagating through the waveguide and outputs an electrical signal.

[0003] Prior art literature Non-patent literature Non-patent literature 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 Problems to be solved by the invention Light loss occurs between the substrate's waveguide and the bonded photodiode. Reducing this light loss can improve light sensitivity. Therefore, an object of the present invention is to provide a light-receiving element and a method for manufacturing the same that can reduce this light loss.

[0004] Means used to solve problems The light-receiving element according to the present invention comprises: 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 having a waveguide, the photodiode comprising a first semiconductor layer, a light-absorbing layer, and a second semiconductor layer, the first semiconductor layer being in contact with the silicon layer, the light-absorbing layer and the second semiconductor layer being stacked in that order on a surface of the first semiconductor layer opposite to 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 plate portion, the protrusion being connected to the first plate portion and protruding from the first plate portion to a position overlapping with the waveguide.

[0005] Effects of the Invention According to the present invention, a light-receiving element capable of reducing light loss and a method for manufacturing the light-receiving element can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0007] Figure 1B This is a perspective view illustrating a light receiving element.

[0008] Figure 1C This is an enlarged view of the protrusion.

[0009] Figure 2A It is a cross-sectional view illustrating a light receiving element.

[0010] Figure 2B It is a cross-sectional view illustrating a light receiving element.

[0011] Figure 3 This is a diagram illustrating light loss.

[0012] Figure 4A This is a plan view illustrating a method for manufacturing a light-receiving element.

[0013] Figure 4B This is a plan view illustrating a method for manufacturing a light-receiving element.

[0014] Figure 4C This is a plan view illustrating a method for manufacturing a light-receiving element.

[0015] Figure 5A This is a plan view illustrating a protruding portion of a light-receiving element according to Modification 1.

[0016] Figure 5B This is a plan view illustrating a protruding portion of a light-receiving element according to Modification 2.

[0017] Figure 5C This is a plan view illustrating a protruding portion of a light-receiving element according to Modification 3.

[0018] Figure 5D This is a plan view illustrating a protruding portion of a light-receiving element according to Modification 4.

[0019] Figure 6A This is a perspective view illustrating a light receiving element according to the second embodiment.

[0020] Figure 6B This is a diagram illustrating light loss.

[0021] Figure 7 This is a perspective view illustrating a light receiving element according to the third embodiment.

[0022] Description of Reference Numerals 10, 12: substrate; 11: insulating film; 14: buried oxide layer; 16: Silicon layer; 20: waveguide; 21, 55, 56: cone; 22: concave part; 24: platform; 26, 52: plate; 30: photodiode; 32, 36: semiconductor layer; 34: light absorbing layer; 38: contact layer; 40, 42: electrodes; 44, 46: pads; 50: protrusion; 53: Partial; 54: countertop; 100, 200, 300: light receiving elements. DETAILED DESCRIPTION

[0023] [Description of Embodiments of the Invention] First, the contents of the embodiments of the present disclosure will be listed and described.

[0024] One embodiment 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 having a waveguide, the photodiode including a first semiconductor layer, a light-absorbing layer, and a second semiconductor layer, the first semiconductor layer being in contact with the silicon layer, the light-absorbing layer and the second semiconductor layer being stacked in this order on a surface of the first semiconductor layer opposite to 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 plate portion, the protrusion being connected to the first plate portion and protruding from the first plate portion to a position overlapping with the waveguide. Since 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.

[0025] (2) In the above (1), the protrusion may have a first tapered portion having a shape tapering toward the front end along the extending direction of the waveguide. Light is gradually transferred from the waveguide to the photodiode, effectively reducing light loss.

[0026] (3) In the above (1) or (2), the length of the protrusion may be 2 μm or more. This can reduce light loss.

[0027] (4) In any one of the above (1) to (3), the front end of the protrusion may be a curved surface. This makes it difficult for light to be reflected, thereby reducing light loss.

[0028] (5) In any of the above (1) to (4), the photodiode may have a mesa, the mesa including the light absorbing layer and the second semiconductor layer, located on the first plate portion and facing the protrusion in the direction in which the waveguide extends. Light propagates in the waveguide, is transferred to the photodiode at the protrusion, and is absorbed by the light absorbing layer of the mesa. The photodiode can detect light.

[0029] (6) In the above (5), the mesa may have a second tapered portion having a shape tapering along the extending direction of the waveguide. This can reduce light loss.

[0030] (7) In the above (6), the length of the second tapered portion may be 5 μm or more. This can reduce light loss.

[0031] (8) In the above (5), the silicon layer may have a recessed portion and a second plate portion, wherein the recessed portion is a portion recessed relative to the second plate portion and is located on both sides of the waveguide, the waveguide is connected to an end portion of the second plate portion, and the first plate portion of the photodiode is bonded to the second plate portion. Light is absorbed by the photodiode on the second plate portion, enabling light detection.

[0032] (9) In the above (8), the second plate portion may extend outward from the first plate portion, and the waveguide may extend outward from the protrusion portion. Even if a liquid such as an etchant enters the recessed portion, the lower surface of the photodiode is unlikely to come into contact with the liquid. Etching from the lower surface can be prevented.

[0033] (10) A method for manufacturing a light-receiving element, wherein the method comprises: a step of bonding a photodiode formed of a III-V compound semiconductor to a silicon layer of a substrate; and a step of forming a plate portion and a protrusion portion on the photodiode, wherein the silicon layer has a waveguide, 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, 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, the second semiconductor layer has a second conductivity type, the first semiconductor layer has the protrusion portion and the plate portion, the protrusion portion is connected to the plate portion, and protrudes from the plate portion to a position overlapping with the waveguide. Since the photodiode has the protrusion portion, light is less likely to be reflected and scattered at the interface between the waveguide and the photodiode, thereby reducing light loss.

[0034] [Details of Embodiments of the Invention] Specific examples of light-receiving elements and methods for manufacturing light-receiving elements according to embodiments of the present invention are described below with reference to the accompanying drawings. It should be noted that the present invention is not limited to these examples, but is defined by the claims, and is intended to encompass all modifications within the meaning and scope of the claims.

[0035] <First embodiment> (Light receiving element) Figure 1A This is a plan view illustrating the light receiving element 100 according to the first embodiment. Figure 1B It is a perspective view illustrating the light receiving element 100 . Figure 1C This is an enlarged view of the protrusion 50. Figures 1A to 1C In the example, the insulating film is omitted. Figure 1B In the figure, the electrodes are omitted. Figure 2A as well as Figure 2B 2 is a cross-sectional view illustrating the light receiving element 100 . Figure 2A Along Figure 1A The cross section along line AA is illustrated. Figure 2B Along Figure 1A The cross section along line BB is shown in FIG.

[0036] like Figure 1A as well as Figure 1B As shown, light receiving element 100 is a hybrid light receiving element having a substrate 10 and a photodiode 30. Photodiode 30 is bonded to the upper surface of substrate 10. The Z-axis direction is the normal direction to the upper surface of substrate 10. The X-axis direction is parallel to the waveguide. The Y-axis direction is orthogonal to the X-axis and Z-axis directions.

[0037] The substrate 10 includes a waveguide 20, a recess 22, a terrace 24, and a plate portion 26 (second plate portion). The waveguide 20 and recess 22 are parallel to the X-axis. Recesses 22 are provided on both sides of the waveguide 20 in the Y-axis direction. Terraces 24 are provided outside the recess 22.

[0038] exist Figure 1A In the figure, a waveguide 20, a recess 22, and a platform 24 are provided on the left. A plate 26 is provided on the right. The platform 24 and the plate 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 overlapping with the photodiode 30. The waveguide 20 is connected to one end of the plate 26. In the Y-axis direction, the plate 26 has a greater width than the waveguide 20 and is connected to the waveguide 20 and the platform 24.

[0039] like Figure 2A as well as Figure 2B As shown, substrate 10 is an SOI (Silicon on Insulator) substrate, comprising a substrate 12, a buried oxide layer 14, and a silicon (Si) layer 16 stacked sequentially in the Z-axis direction. Substrate 12 is formed, for example, of Si. Buried oxide layer 14 is formed, for example, of silicon oxide (SiO2). Buried oxide 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 by insulating film 11. Insulating film 11 is formed, for example, of 1 μm thick SiO2. 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 relative to light with a wavelength of 1.55 μm. Waveguide 20, recess 22, terrace 24, and plate 26 are provided in silicon layer 16 of substrate 10.

[0040] The waveguide 20, terrace 24, and plate 26 protrude further in the Z-axis direction (upward) than the recess 22. The surfaces of the waveguide 20, terrace 24, and plate 26 are located at the same height. The recess 22 is recessed relative to the surfaces of the waveguide 20, terrace 24, and plate 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 to the middle of the silicon layer 16 in the Z-axis direction, or may penetrate the silicon layer 16 and extend to the buried oxide layer 14. The insulating film 11 is embedded in the recess 22.

[0041] The photodiode 30 is a semiconductor element formed of a III-V compound semiconductor. The photodiode 30 is bonded to the terrace 24 and the plate portion 26 of the silicon layer 16. Figure 1B as well as Figure 2BAs shown, the photodiode 30 includes a semiconductor layer 32 (first semiconductor layer), a light absorbing 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 absorbing 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.

[0042] Semiconductor layer 32 is formed, for example, of n-type (first conductivity type) indium phosphide (n-InP). Semiconductor layer 32 is doped with, for example, silicon (Si). Light absorption layer 34 is formed, for example, of undoped indium gallium arsenide (InGaAs). Semiconductor layer 36 is formed, for example, of p-type (second conductivity type) indium phosphide (p-InP). Contact layer 38 is formed, for example, of p+-type indium gallium arsenide ((p+)-InGaAs). Semiconductor layer 36 and contact layer 38 are doped with, for example, zinc (Zn). The semiconductor layers of photodiode 30 may also be formed of Group III-V compound semiconductors other than those listed above.

[0043] like Figure 1A as well as Figure 1B As shown, the photodiode 30 has a protrusion 50, a plate portion 52 (first plate portion), and a mesa 54. Figure 1B As shown, the protrusion 50 and the plate portion 52 include the semiconductor layer 32. The mesa 54 includes the light absorbing layer 34, the semiconductor layer 36 and the contact layer 38. Figure 2A As shown, the protrusion 50 is covered by the insulating film 11. Figure 2B As shown, the plate portion 52 and the mesa 54 are also covered with the insulating film 11 .

[0044] like Figure 1A as well as Figure 1B As shown, plate portion 52 is provided over a larger area than mesa 54 and is bonded to terrace 24 and plate portion 26 of silicon layer 16. The width of plate portion 52 is greater than the width of protrusion 50. Protrusion 50 is connected to one end of plate portion 52 and protrudes from this end toward a position overlapping with waveguide 20. Protrusion 50 is generally tapered (first tapered portion), tapering toward the tip along the X-axis. The width of protrusion 50 increases as it approaches plate portion 52 and decreases as it moves away from plate portion 52. Figure 1C The width W1 of the portion of the protrusion 50 connected to the plate portion 52 shown is, for example, 2 μm. The length L1 of the protrusion 50 in the X-axis direction is, for example, not less than 2 μm and not more than 100 μm. The tip of the protrusion 50 is a curved surface. The protrusion 50 is line-symmetrical about the X-axis direction.

[0045] The mesa 54 is located on the plate portion 52 and faces the protruding portion 50 in the X-axis direction. The mesa 54 has a rectangular parallelepiped shape. Figure 1BThe length L2 of mesa 54 shown is, for example, 5 μm to 50 μm, and is 30 μm as an example. The width W2 of mesa 54 is, for example, 0.5 μm to 6 μm, and is 2 μm as an example. Waveguide 20 extends to the end of mesa 54 opposite to protrusion 50. A pin junction is formed by n-type semiconductor layer 32, light absorbing layer 34, and p-type semiconductor layer 36.

[0046] like Figure 1A As shown, light receiving element 100 includes electrodes 40 and 42, and pads 44 and 46. The electrodes and pads are formed of metal. Electrodes 40 serve as cathodes and are electrically connected to semiconductor layer 32. Pad 44 is electrically connected to electrodes 40. Electrode 42 serves as an anode and is electrically connected to contact layer 38. Pad 46 is electrically connected to electrode 42.

[0047] 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. Pad 44 is, for example, the same size as 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.

[0048] 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 can also be between 1.26 μm and 1.63 μm. 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. Light propagates through the waveguide 20 and is transferred from the waveguide 20 to the photodiode 30. The light absorbing layer 34 of the photodiode 30 absorbs the light, generating photocarriers (hole-electron pairs). These photocarriers are output as a photocurrent.

[0049] Photodiode 30 has a tapered protrusion 50. Light is transferred from waveguide 20 to photodiode 30 via protrusion 50. Protrusion 50 minimizes reflection and scattering of light between waveguide 20 and photodiode 30, reducing light loss. Photodiode 30 absorbs high-output light, improving its light sensitivity.

[0050] The mode of light propagating in the waveguide 20 is a single mode. A higher-order mode may also occur in the protrusion 50. The photodiode 30 can absorb light in both the single mode and the higher-order mode and output an electrical signal.

[0051] Figure 3 This is a diagram illustrating light loss. The horizontal axis represents the length L1 of the protrusion 50 . Figure 3The horizontal axis of 0 indicates 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 calculated results of light loss at the interface between the waveguide 20 and the photodiode 30. The wavelength of light used for the loss calculation is 1.55 μm in a vacuum. The approximate wavelength of light propagating through the silicon layer 16 is the value obtained by dividing the wavelength in a vacuum 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.

[0052] When the length L1 is 0, the optical loss is 0.14 dB. Protrusion 50 is provided in photodiode 30, reducing optical loss. When the length L1 of protrusion 50 is 2 μm or greater, optical loss is reduced to approximately 0.02 dB. When the length L1 of protrusion 50 is greater than four times the wavelength of light passing through protrusion 50, optical loss is reduced to 0.02 dB or less. When the length L1 is between 6 μm and 50 μm, optical loss is 0.02 dB or less.

[0053] (Manufacturing Method) Silicon layer 16 of substrate 10 is dry-etched, for example. The portion exposed from the mask (not shown) is etched, forming recess 22. The portion covered by the mask (not shown) is not etched. Waveguide 20, terrace 24, and plate 26 are formed.

[0054] On an InP substrate, different from the SOI substrate (substrate 10), a contact layer 38, a semiconductor layer 36, a light absorbing layer 34, and a semiconductor layer 32 are epitaxially grown in this order by methods such as metal organic chemical vapor deposition (MOCVD). This InP substrate is diced to form the photodiode 30. The photodiode 30 immediately after dicing is a rectangular parallelepiped and lacks the protrusion 50 or the mesa 54.

[0055] Figures 4A to 4C 1 is a top view illustrating a method for manufacturing the light receiving element 100. Figure 4A As shown, a photodiode 30 is bonded to the upper surface of substrate 10. During the bonding process, plasma is irradiated onto one surface of silicon layer 16 and the surface of semiconductor layer 32 of photodiode 30 to activate these surfaces. The surface of semiconductor layer 32 is brought into contact with the surface of silicon layer 16, bonding photodiode 30 to silicon layer 16. For example, photodiode 30 covers the entire upper surface of silicon layer 16 and is positioned above waveguide 20, recess 22, terrace 24, and plate 26. After bonding, wet etching is performed to remove the InP substrate in photodiode 30. Semiconductor layer 32 remains on contact layer 38.

[0056] like Figure 4BAs shown, mesas 54 are formed on photodiode 30. The portions of contact layer 38, semiconductor layer 36, and light absorbing layer 34 exposed by the mask (not shown) are removed by dry etching. Mesas 54 are formed in the portions covered by the mask. For example, a chlorine-based etching gas is used in dry etching. After dry etching, the mask is removed. Semiconductor layer 32 of photodiode 30 covers the upper surface of substrate 10.

[0057] like Figure 4C As shown, a plate portion 52 and a protrusion 50 are formed on 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 by the mask is removed by dry etching. The plate portion 52 and the protrusion 50 are formed by dry etching. After the dry etching, the mask is removed.

[0058] The electrodes 40 and 42, the pads 44 and 46 are formed by vacuum deposition and lift-off methods. The light-receiving element 100 is formed by cutting the substrate 10.

[0059] 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. The protrusion 50 in the photodiode 30 reduces light reflection and scattering at the interface between the waveguide 20 and the photodiode 30, thereby reducing light loss. Since the photodiode 30 can absorb high-output light, the light receiving sensitivity of the light receiving element 100 is improved.

[0060] like Figures 1A to 1C As shown, the protrusion 50 is a tapered portion. The refractive index changes continuously along the X-axis. Light gradually transfers from the waveguide 20 to the photodiode 30, effectively reducing light loss.

[0061] like Figure 3 As shown in FIG. 1 , by setting the length L1 of the protrusion 50 to be 2 μm or more, the light loss can be significantly reduced. When the length L1 is in the range of 6 μm or more and 50 μm or less, the light loss is 0.02 dB or less. Figure 3 In the example, even if the protrusion 50 is extended to 20 μm or more, the light loss is the same. For example, the length L1 can be 2 μm or more and 20 μm or less. The length L1 can also 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.

[0062] like Figure 1C As shown, the front end of the protrusion 50 is curved. When viewed from above, the front end is arc-shaped or elliptical. The front end of the protrusion 50 is not perpendicular to the direction of light propagation. This makes it less likely that light will be reflected by the front end of the protrusion 50, allowing it to more easily reach the photodiode 30. This reduces light loss.

[0063] In the waveguide 20, the mode of light is, for example, a single mode. The photodiode 30 absorbs both single mode and high-order mode. Therefore, high-order modes can also be excited at the protrusion 50. The high-order mode is wider than the single mode in the cross section of the photodiode 30. Light containing multiple high-order modes is widely distributed from the semiconductor layer 32 to the semiconductor layer 36 in the cross section. The light intensity is not localized in the light absorption layer 34. Since the light intensity is not localized, the photocarriers are also not localized. The photodiode 30 has high responsiveness not only to low-frequency light signals, but also to high-frequency light signals. For example, the light receiving element 100 can effectively perform high-speed operations above 50 GHz.

[0064] 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.

[0065] The photodiode 30 includes a protrusion 50, a plate portion 52, and a mesa 54. The protrusion 50 overlaps the waveguide 20. The mesa 54 faces the protrusion 50 in the direction in which the waveguide 20 extends. Light propagating through the waveguide 20 is transferred to the photodiode 30 at the protrusion 50 and absorbed by the light absorbing layer 34 of the mesa 54. The photodiode 30 can detect light.

[0066] The protrusion 50 and plate portion 52 are formed from the n-type semiconductor layer 32. The mesa 54 includes the light absorbing layer 34, the p-type semiconductor layer 36, and the 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 then output. The light receiving element 100 can detect light.

[0067] Parasitic capacitance is generated on mesa 54. The larger the mesa 54, the higher the parasitic capacitance. When viewed from above, the area of ​​mesa 54 is smaller than the area of ​​plate portion 52. The smaller mesa 54 reduces parasitic capacitance, minimizing its effect on the operation of light-receiving element 100.

[0068] Semiconductor layer 32 is formed, for example, of n-InP. Semiconductor layer 36 is formed, for example, of p-InP. Light absorbing layer 34 is formed, for example, of InGaAs. Semiconductor layer 32, semiconductor layer 36, and light absorbing layer 34 may also include compound semiconductors other than those listed above. Semiconductor layer 32 may be p-type, while semiconductor layer 36 and contact layer 38 may be n-type.

[0069] The silicon layer 16 of the substrate 10 includes a waveguide 20, a recess 22, a terrace 24, and a plate portion 26. The waveguide 20 is connected to the end of the plate portion 26. The plate portion 52 of the photodiode 30 is bonded to the plate portion 26. Light propagating through the waveguide 20 is transferred to the photodiode 30 and absorbed by the photodiode 30 on the plate portion 26. The light receiving element 100 can detect light.

[0070] (Variation 1 and Variation 2) Figure 5A This is a plan view illustrating the protrusion 50 of the light receiving element according to Modification 1. Figure 5B This is a top view illustrating the protrusion 50 of the light receiving element according to the second modification. The description of the same structure as the first embodiment is omitted. Figure 5A As shown in FIG. 1 , in the modification 1, the front end of the protrusion 50 is a plane perpendicular to the X-axis. Figure 5B As shown, in Modification 2, the front end of the protrusion 50 is an inclined surface, which is inclined with respect to the X-axis direction and the Y-axis direction. The protrusion 50 is asymmetrical with respect to the X-axis direction.

[0071] In Modification 1 and Modification 2, since the photodiode 30 has the protrusion 50, light loss can be reduced. Figure 5A As shown, if the surface of the front end of the protrusion 50 is perpendicular to the propagation direction of light (X-axis direction), there is a risk that light will be reflected by the surface. Figure 5B As shown, when the front end of the protrusion 50 is inclined with respect to the X-axis direction, light is hardly reflected.

[0072] (Variation 3 and Variation 4) Figure 5C This is a plan view illustrating the protrusion 50 of the light receiving element according to Modification 3. Figure 5D This is a top view illustrating the protrusion 50 of the light receiving element according to Modification 4. The description of the same configuration as that of the first embodiment will be omitted. Figure 5C As shown in FIG. 3 , in the modification example 3, the protrusion 50 has a portion 53 and a tapered portion 55. The planar shape of the portion 53 is a straight line. The tapered portion 55 is located at the front end of the protrusion 50 and has a tapered shape. Figure 5D As shown, in the fourth modification, the protrusion 50 is linear as a whole.

[0073] In Modification 3 and Modification 4, since the photodiode 30 has the protrusion 50, light loss can be reduced. Figure 5D As shown, when the entire protrusion 50 is linear, there is a risk of light loss. In addition, since the front end surface is perpendicular to the propagation direction of light, there is a risk of increased reflection. Figure 5CAs shown in FIG. 5 , by providing the protrusion 50 with a tapered portion 55, light is gradually transferred from the waveguide 20 to the photodiode 30. This can reduce light loss. Figure 1C As shown, the entire protrusion 50 may be a tapered portion. It is sufficient that at least a portion of the protrusion 50 is a tapered portion.

[0074] <Second embodiment> Figure 6A This is a perspective view illustrating a light receiving element 200 according to the second embodiment. The same configuration as that of the first embodiment is omitted. Figure 6A As shown, the mesa 54 of the photodiode 30 has a tapered portion 56 (second tapered portion). The tapered portion 56 is located in the 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 arranged in this order.

[0075] According to the second embodiment, the semiconductor layer 32 has the protrusion 50. The mesa 54 has the tapered portion 56. The photodiode 30 has a two-stage tapered structure, which can improve the optical coupling efficiency between the waveguide 20 and the light absorbing layer 34 and reduce light loss.

[0076] Figure 6B This is a diagram illustrating light loss. The horizontal axis represents the length L1 of the protrusion 50. The vertical axis represents the calculation result of the light loss at the interface between the waveguide 20 and the photodiode 30. The protrusion 50 has a conical shape. The width W1 of the protrusion 50 is set to 2 μm. The length L1 of the protrusion 50 of the semiconductor layer 32 and the length L4 of the cone 56 of the mesa 54 in the X-axis direction are changed. Black dots and solid lines represent an example where the length L4 is 0. Dashed lines and quadrilaterals represent an example where the length L4 is 5 μm. Solid lines and diamonds represent an example where the length L4 is 10 μm. Single-dot chain lines and double circles represent an example where the length L4 is 15 μm. Dashed lines and triangles represent an example where the length L4 is 20 μm.

[0077] like Figure 6BAs shown, by setting the length L4 of the tapered portion 56 to, for example, 5 μm to 20 μm, light loss can be reduced compared to a case without the tapered portion 56 (L4 = 0). When compared with the same length L1 of the protrusion 50, the longer the tapered portion 56, the lower the light loss. Regardless of the length L4, within the range of 7 μm to 50 μm, light loss is below 0.02 dB. The length of the mesa 54 in the X-axis direction is 30 μm. Increasing the length L4 of the tapered portion 56 while maintaining the length of the mesa 54 constant reduces the area of ​​the mesa 54 when viewed from above. This reduces the volume of the light absorbing layer 34. This creates a risk of insufficient light absorption in the photodiode 30. To ensure sufficient light absorption by the photodiode 30, the length L4 may be less than the length L2 of the mesa 54.

[0078] <Third embodiment> Figure 7 This is a perspective view illustrating a light receiving element 300 according to the third embodiment. Description of the same configurations as those in the first embodiment or the second embodiment will be omitted.

[0079] like Figure 7 As shown, the plate portion 26 of the substrate 10 is located in a larger area than the plate portion 52 of the photodiode 30 and protrudes outward from the plate portion 52 in the X-axis and Y-axis directions. The waveguide 20 and the recess 22 extend to the end of the plate portion 26 and do not extend to a position overlapping with the plate portion 52. In other words, the plate portion 52 does not protrude into the recess 22.

[0080] The waveguide 20 has a tapered portion 21. The width of the tapered portion 21 increases as it approaches the plate portion 26 and decreases as it moves away from the plate portion 26. The portion of the waveguide 20 other than the tapered portion 21 has a constant width. The protrusion 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 that of the protrusion 50. The waveguide 20 extends outward beyond the protrusion 50. The protrusion 50 is entirely located above the tapered portion 21 and does not protrude into the recess 22.

[0081] The mesa 54 of the photodiode 30 has a tapered portion 56 . The tapered portion 56 is located above the protrusion 50 . The portion of the mesa 54 that is not tapered is located above the plate portion 52 .

[0082] According to the third embodiment, the plate portion 52 of the photodiode 30 is bonded to the plate portion 26 of the silicon layer 16. The plate portion 26 extends outward from the plate portion 52. The waveguide 20 extends 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 a gas such as an etching gas used for dry etching or a liquid such as an etchant enters the recess 22, the gas and liquid are unlikely to contact the lower surface of the photodiode 30. Etching of the photodiode 30 from the lower surface is unlikely, preventing peeling and the like.

[0083] The waveguide 20 has a tapered portion 21 corresponding to the tapered protrusion 50. Since the protrusion 50 is joined to the tapered portion 21, the protrusion 50 is hardly etched by the etchant in the recess 22. 5A to 5D When the shape of the protrusion 50 is changed, the waveguide 20 may also have a shape corresponding to the protrusion 50 .

[0084] The waveguide 20, the protrusion 50, and the mesa 54 each have a tapered portion. Since the light receiving element 300 has a three-stage tapered structure, light loss can be reduced.

[0085] The mesa 54 may be a rectangular parallelepiped as in the first embodiment, and the photodiode 30 may be bonded to the plate portion 26 and not exposed in the recess 22 as in the third embodiment.

[0086] As mentioned above, although embodiment of this invention is described in detail, this invention is not limited to the said specific embodiment, Various deformation|transformation and modification are possible within the range of the summary of this invention described in a claim.

Claims

1. A light receiving element, wherein: The light receiving element comprises: a substrate having a silicon layer; as well as A photodiode formed of a III-V compound semiconductor is bonded to the silicon layer. The silicon layer has a waveguide, The photodiode comprises a first semiconductor layer, a light absorbing layer, and a second semiconductor layer. The first semiconductor layer is in contact with the silicon layer, The light absorbing layer and the second semiconductor layer are stacked in this order on the 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 plate portion, The protruding portion is connected to the first plate portion and protrudes from the first plate portion toward a position overlapping with the waveguide.

2. The light-receiving element according to claim 1, wherein The protrusion has a first tapered portion, The first tapered portion has a shape that tapers toward the front end along the extending direction of the waveguide.

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

4. The light-receiving element according to claim 1 or 2, wherein The front end of the protrusion is a curved surface.

5. The light-receiving element according to claim 1 or 2, wherein The photodiode has a mesa, The mesa includes the light absorbing layer and the second semiconductor layer, is located on the first plate portion, and faces the protrusion in the extending direction of the waveguide. The light-receiving element according to claim 5 , wherein: The table has a second tapered portion, The second tapered portion has a shape that tapers toward the front end along the extending direction of the waveguide.

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

8. The light-receiving element according to claim 5, wherein The silicon layer has a concave portion and a second plate portion, The concave portion is a portion recessed from the second plate portion and is located on both sides of the waveguide. The waveguide is connected to the end of the second plate portion, The first plate portion and the second plate portion of the photodiode are bonded.

9. The light receiving element according to claim 8, wherein The second plate portion extends outwards beyond the first plate portion, The waveguide extends outward from the protrusion.

10. A method for manufacturing a light-receiving element, wherein: The manufacturing method of the light receiving element comprises: A step of bonding a photodiode formed of a III-V compound semiconductor to the silicon layer of the substrate; as well as In the process of forming the plate portion and the protrusion portion of the photodiode, The silicon layer has a waveguide, The photodiode comprises a first semiconductor layer, a light absorbing layer, and a second semiconductor layer. The first semiconductor layer is in contact with the silicon layer, The light absorbing layer and the second semiconductor layer are stacked in this order on the 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 plate portion, The protruding portion is connected to the plate portion and protrudes from the plate portion toward a position overlapping with the waveguide.

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