Photodetector with contiguous slot waveguide structure

Abstract

The invention relates to photodetectors with contiguous slot waveguide structures. Structures including photonic chips of photodetectors and methods of forming such structures are provided. The structure includes a photodetector including a gasket and a semiconductor layer on the gasket. The structure also includes a waveguide structure including a first waveguide core, a second waveguide core, a slot between the first waveguide core and the second waveguide core, and a plurality of waveguide core segments. The waveguide structure adjoins a side edge of the gasket, and the side edge of the gasket is adjacent to the semiconductor layer. Each of the plurality of waveguide core segments includes a portion disposed in the slot.

Description

Technical Field

[0001] The present disclosure relates to a photonic chip, and more particularly to a structure of a photonic chip including a photodetector and a method of forming such a structure. Background Art

[0002] Photonic chips are used in many applications and systems, including but not limited to data communication systems and data computing systems. A photonic chip includes a photonic integrated circuit, which is composed of photonic elements such as modulators, polarizers, and optical couplers for manipulating light received from a light source (such as an optical fiber or a laser). A photodetector can be used in the photonic integrated circuit to convert light (which can be modulated into an optical signal) into an electrical signal. The responsivity of a photodetector is a measure of the photoelectric conversion efficiency. The bandwidth of a photodetector is a measure of the response speed of the photodetector to changes in incident optical power. Generally, design modifications to improve the bandwidth of a photodetector will reduce the responsivity.

[0003] There is a need to improve the structure of a photonic chip including a photodetector and a method of forming such a structure. Summary of the Invention

[0004] In one embodiment of the present invention, a structure for a photonic chip is provided. The structure includes a photodetector, which includes a pad and a semiconductor layer on the pad. The structure further includes a waveguide structure, which includes a first waveguide core, a second waveguide core, a slot between the first waveguide core and the second waveguide core, and a plurality of waveguide core segments. The waveguide structure abuts a side of the pad, and the side of the pad is adjacent to the semiconductor layer. Each of the plurality of waveguide core segments includes a portion disposed in the slot.

[0005] In one embodiment of the present invention, a method of forming a structure of a photonic chip is provided. The method includes forming a photodetector, which includes a pad and a semiconductor layer on the pad, and forming a waveguide structure, which includes a first waveguide core, a second waveguide core, a slot between the first waveguide core and the second waveguide core, and a plurality of waveguide core segments. The waveguide structure abuts a side of the pad, and the side of the pad is adjacent to the semiconductor layer, and each of the plurality of waveguide core segments includes a portion disposed within the slot. Brief Description of the Drawings

[0006] The drawings are incorporated into and form a part of this specification, which illustrate various embodiments of the present invention and, together with the general description of the present invention given above and the detailed description of the embodiments given below, are used to explain the embodiments of the present invention. In the drawings, the same reference numerals represent the same features in each view.

[0007] Figure 1 is a top view of the structure in the initial manufacturing stage of the processing method according to an embodiment of the present invention.

[0008] Figure 2 is generally along Figure 1 a cross-sectional view taken along line 2-2 in

[0009] Figure 2A is generally along Figure 1 a cross-sectional view taken along line 2A-2A in

[0010] Figure 3 is Figure 1 、 Figure 2 、 Figure 2A a top view of the structure in the manufacturing stage of the processing method after

[0011] Figure 4 is generally along Figure 3 a cross-sectional view taken along line 4-4 in

[0012] Figure 4A is generally along Figure 3 a cross-sectional view taken along line 4A-4A in

[0013] Figure 5 、 Figure 5A is Figure 3 、 Figure 4 、 Figure 4A a cross-sectional view of the structure in the manufacturing stage of the processing method after

[0014] Figure 6 is a top view of the structure according to an alternative embodiment of the present invention.

[0015] Figure 7 is a top view of the structure according to an alternative embodiment of the present invention.

[0016] Figure 8 、 Figure 8A is a cross-sectional view of the structure according to an alternative embodiment of the present invention.

[0017] Figure 9 is a top view of the structure according to an alternative embodiment of the present invention.

[0018] Figure 10 is a top view of the structure according to an alternative embodiment of the present invention.

[0019] Figure 11 is a top view of the structure according to an alternative embodiment of the present invention. Detailed Description

[0020] Refer to Figure 1 、Figure 2 , Figure 2A According to an embodiment of the present invention, the structure 10 includes waveguide cores 11, 12, 13 and a photodetector 14 located on (and above) the dielectric layer 16 and the semiconductor substrate 18. In one embodiment, the dielectric layer 16 may be composed of a dielectric material (such as silicon dioxide), and the semiconductor substrate 18 may be composed of a semiconductor material (such as single crystal silicon). In one embodiment, the dielectric layer 16 may be a buried oxide layer of a silicon-on-insulator substrate, the dielectric layer 16 may be disposed between the waveguide cores 11, 12, 13 and the semiconductor substrate 18, and the dielectric layer 16 may provide a low-index cladding for the waveguide core 12 and the photodetector 14.

[0021] The photodetector 14 includes a pad 24 having side edges 23, a side edge 25 opposite to the side edge 23, a side edge 27, and a side edge 29 opposite to the side edge 27. The side edges 23, 25, 27, 29 may surround the outer periphery of the pad 24, and the side edges 23, 25, 27, 29 may extend to the dielectric layer 16. The photodetector 14 further includes a semiconductor layer 26 that provides a light absorption layer disposed on the pad 24 and spaced inwardly from the outer periphery of the pad 24. The semiconductor layer 26 may have sidewalls 34 near the side edge 23 of the pad 24, sidewalls 35 near the side edge 25 of the pad 24, sidewalls 37 near the side edge 27 of the pad 24, and sidewalls 39 near the side edge 29 of the pad 24. The semiconductor layer 26 longitudinally extends on the pad 24 from the sidewall 34 to the sidewall 35 along the longitudinal axis 36. In one embodiment, the semiconductor layer 26 may be equidistantly disposed between the side edges 27 and 29.

[0022] The waveguide core 12 and the waveguide core 13 may be symmetrically located on opposite sides of the longitudinal axis 36 of the semiconductor layer 26 along the side edge 23 of the pad 24. The waveguide cores 12, 13 may longitudinally extend along their respective longitudinal axes 15, 17. The longitudinal axes 15, 17 of the waveguide cores 12, 13 may be parallel and aligned with the longitudinal axis 36 of the semiconductor layer 26. The waveguide core 12 is disposed near the waveguide core 13, and there is a groove or gap G1 between the waveguide core 12 and the waveguide core 13. In one embodiment, the gap G1 separating the waveguide core 12 from the waveguide core 13 may be centered with respect to the longitudinal axis 36 of the semiconductor layer 26.

[0023] The waveguide cores 12, 13 form a slotted waveguide structure that is configured to direct light from the waveguide core 11 to the photodetector 14. The waveguide structure further includes waveguide core segments 20 that cover or overlay the waveguide cores 12, 13. The waveguide core segments 20 are distributed in a spaced relationship along the longitudinal axis 15 of the waveguide core 12 and the longitudinal axis 17 of the waveguide core 13. In one embodiment, the length dimension of each waveguide core segment 20 may be laterally aligned with the longitudinal axes 15, 17.

[0024] In one embodiment, each waveguide core segment 20 may include a portion located within a gap G1 between the inner sidewall 74 of the waveguide core 12 and the inner sidewall 76 of the waveguide core 13. In one embodiment, each waveguide core segment 20 may include a bridging portion that extends completely across the gap G1 from the inner sidewall 74 of the waveguide core 12 to the inner sidewall 76 of the waveguide core 13, a protruding end portion that protrudes outward from the outer sidewall 75 of the waveguide core 12, and a protruding end portion that protrudes outward from the outer sidewall 77 of the waveguide core 13. The inner sidewall 74 of the waveguide core 12 is disposed adjacent to the inner sidewall 76 of the waveguide core 13 across the gap G1, the outer sidewall 75 of the waveguide core 12 is disposed opposite to the inner sidewall 74, and the outer sidewall 77 of the waveguide core 13 is disposed opposite to the inner sidewall 76.

[0025] The waveguide structure including the waveguide cores 12, 13 and the waveguide core segments 20 has an envelope represented by a smooth curve that follows the opposite edges of the protruding end portions of the waveguide core segments 20. In a representative embodiment, the envelope of the waveguide structure has a constant effective width dimension. In an alternative embodiment, the envelope of the waveguide structure may have a tapered effective width dimension. In an alternative embodiment, the envelope of the waveguide structure may be tapered such that its effective width dimension varies linearly or non-linearly as the distance from the side edge 23 of the spacer 24 decreases. In an alternative embodiment, the envelope of the waveguide structure may be tapered such that its effective width dimension increases linearly or non-linearly as the distance from the side edge 23 of the spacer 24 decreases.

[0026] The waveguide core segments 20 are characterized by a pitch and a width, and adjacent pairs of waveguide core segments 20 are separated by a gap G2. In one embodiment, the waveguide core segments 20 may have a uniform pitch, width, and gap G2. In alternative embodiments, the pitch and the gap G2 of the waveguide core segments 20 may vary with the position along the longitudinal axes 15, 17 of the waveguides 12, 13 and with the position relative to the side edge 23 of the spacer 24. In alternative embodiments, the width of the waveguide core segments 20 may vary with the position relative to the side edge 23 of the spacer 24. In alternative embodiments, the pitch and / or the duty cycle of the waveguide core segments 20 may be apodized (i.e., non-uniform) to define a non-periodic arrangement. In one embodiment, the period of the waveguide core segments 20 may be equal to half the wavelength of the light received by the structure 10, or an integer multiple of half the wavelength. In alternative embodiments, the sidewalls of the bridging portions of the waveguide core segments 20 may have a curvature, and the protruding ends of the waveguide core segments 20 may be rounded. In one embodiment, the dimensions and positions of the waveguide core segments 20 and the gap G2 may be small enough such that the waveguide core segments 20 are configured to form a sub-wavelength grating that does not radiate or reflect light at the operating wavelength (such as an operating wavelength in the range of 400 nanometers to 3,000 nanometers).

[0027] A waveguide structure including waveguides 12, 13 and waveguide core segments 20 abuts (i.e., shares a boundary with) the side edge 23 of the spacer 24. In one embodiment, the waveguides 12 and 13 of the waveguide structure may abut the side edge 23 of the spacer 24. In a representative embodiment, the protruding end and the bridging portion of one of the waveguide core segments 20 may also abut the side edge 23 of the spacer 24.

[0028] A waveguide structure including waveguides 12, 13 and waveguide core segments 20 provides a feature of a lattice-like or grid-like arrangement located between the waveguide 11 and the photodetector 14. The waveguide 11 provides an input to the structure 10, which feeds light into the waveguide structure. In the illustrated embodiment, the waveguide 11 may be non-slotted and solid, and may butt against both of the waveguides 12, 13 of the waveguide structure.

[0029] In one embodiment, the waveguide cores 11, 12, 13, the waveguide core segment 20, and the spacer 24 of the photodetector 14 may be composed of a material having a refractive index greater than that of silicon dioxide. In one embodiment, the waveguide cores 11, 12, 13, the waveguide core segment 20, and the spacer 24 of the photodetector 14 may be composed of a semiconductor material. In one embodiment, the waveguide cores 11, 12, 13, the waveguide core segment 20, and the spacer 24 of the photodetector 14 may be composed of single-crystalline silicon. The waveguide cores 11, 12, 13, the waveguide core segment 20, and the spacer 24 of the photodetector 14 may be formed by patterning a layer composed of their constituent materials using photolithography and etching processes. In one embodiment, the waveguide cores 11, 12, 13, the waveguide core segment 20, and the spacer 24 of the photodetector 14 may be formed by patterning the semiconductor material (e.g., single-crystalline silicon) of the device layer of a silicon-on-insulator substrate.

[0030] The semiconductor layer 26 of the photodetector 14 may be composed of a light-absorbing material that can generate charge carriers from the photons of the absorbed light through photoelectric conversion. In one embodiment, the semiconductor layer 26 may be formed by an epitaxial growth process. In one embodiment, the semiconductor layer 26 may be epitaxially grown inside and outside the trench 22 patterned in the spacer 24 such that the semiconductor layer 26 includes a lower portion disposed below the top surface 28 of the spacer 24 and an upper portion disposed above the top surface 28 of the spacer 24. A hardmask composed of a dielectric material may be disposed on the top surface 28 of the spacer 24 and around the trench 22 during the epitaxial growth process and removed after the epitaxial growth process.

[0031] In one embodiment, the semiconductor layer 26 may be composed of an intrinsic semiconductor material. In one embodiment, the semiconductor layer 26 may be composed of intrinsic germanium. In one embodiment, the semiconductor layer 26 may be composed of intrinsic silicon germanium. In an alternative embodiment, the semiconductor layer 26 may be composed of different types of semiconductor materials, such as III-V compound semiconductor materials or silicon.

[0032] In an alternative embodiment, the semiconductor layer 26 may be angled with respect to the longitudinal axes 15, 17 of the waveguide cores 12, 13. In an alternative embodiment, the semiconductor layer 26 may be patterned to provide a convex, concave, or quadrilateral geometry at the sidewall 34, which can effectively minimize the optical return loss. In an alternative embodiment, the waveguide core segment 20 of the waveguide structure may be formed using an inverse design algorithm or an optimization algorithm.

[0033] Reference Figure 3 、 Figure 4 、 Figure 4A, where like reference numerals represent Figure 1 , Figure 2 , Figure 2A like features in

[0034] and in subsequent manufacturing stages, structure 10 may include a doped region 40 formed in a portion of spacer 24 adjacent to sidewall 37 of semiconductor layer 26 and a doped region 42 formed in a portion of spacer 24 adjacent to sidewall 39 of semiconductor layer 26. Semiconductor layer 26 is laterally positioned on spacer 24, between doped region 40 and doped region 42. Doped regions 40, 42 of different conductivity types may extend completely through the entire thickness of spacer 24 to underlying dielectric layer 16. Doped region 40 and doped region 42 may define the anode and cathode of photodetector 14.

[0035] The doped region 42 can be formed, for example, by ion implantation, where the implantation mask has an opening that defines the implantation area of the spacer 24. The implantation mask can include a photoresist layer laid down by a spin coating process, which is pre-baked, exposed to light projected through a photomask, post-exposure baked, and developed with a chemical developer to define an opening above the area of the spacer 24 to be implanted. Implantation conditions such as ion species, dose, and kinetic energy can be selected to adjust the electrical and physical characteristics of the doped region 42. The implantation mask can be stripped after the doped region 42 is formed. In one embodiment, the semiconductor material of the doped region 42 can include an n-type dopant, such as phosphorus or arsenic, that provides n-type conductivity. In an alternative embodiment, since the opening in the implantation mask partially overlaps the semiconductor layer 26, a portion of the semiconductor layer 26 immediately adjacent to the doped region 42 and the lower portion of the spacer 24 can be implanted with an n-type dopant. In an alternative embodiment, the doped region 42 can have a boundary that is laterally spaced from the sidewall 39 of the semiconductor layer 26 such that a portion of the spacer 24 between the semiconductor layer 26 and the doped region 42 is not implanted.

[0036] A portion of the spacer 24 below the semiconductor layer 26 can be composed of an intrinsic semiconductor material (e.g., intrinsic silicon) that is not doped by the ion implantation that forms the doped regions 40, 42. In one embodiment, the intrinsic portion of the spacer 24 can extend from the side 23 of the spacer 24 to the side 25 of the spacer 24 and is located below the semiconductor layer 26. The doped region 40, the intrinsic semiconductor material of the semiconductor layer 26, the portion of the spacer 24 below the semiconductor layer 26, and the doped region 42 can define a lateral p-i-n diode structure that enables the photodetector 14 to function.

[0037] The heavily doped region 41 can be formed by performing masked ion implantation on a portion of the doped region 40 adjacent to the side 27. The heavily doped region 43 can be formed by performing masked ion implantation on a portion of the doped region 42 adjacent to the side 29. The heavily doped region 41 can have the same conductivity type as the doped region 40 but a higher dopant concentration. The heavily doped region 43 can have the same conductivity type as the doped region 42 but a higher dopant concentration.

[0038] Reference Figure 5 、 Figure 5A where like reference numerals indicate Figure 3 、 Figure 4 、 Figure 4Athe same features as those in, and in a subsequent manufacturing stage, a dielectric layer 60 can be formed over the waveguide core 12 and the photodetector 14. In one embodiment, the dielectric layer 60 can be composed of a dielectric material (such as silicon dioxide). The dielectric material portion of the dielectric layer 60 can fill the gap G2 between the waveguide core segments 20. The waveguide core segments 20 and the dielectric material portion within the gap G2 can define a metamaterial structure, where the material constituting the waveguide core segments 20 has a higher refractive index than the dielectric material. The metamaterial structure can be regarded as a homogeneous material with an effective refractive index that lies between the refractive index of the material constituting the waveguide core segments 20 and the refractive index of the dielectric material.

[0039] A conformal dielectric layer 62 can be formed, which extends across the waveguide core 12 and the photodetector 14 and follows the surface topography generated by the semiconductor layer 26. In one embodiment, the conformal dielectric layer 62 can be composed of a dielectric material (such as silicon nitride). A dielectric layer 64 can be formed over the conformal dielectric layer 62. In one embodiment, the dielectric layer 64 can be composed of a dielectric material (such as silicon dioxide), whose refractive index is lower than that of the material of the waveguide core 12. The dielectric layer 64 can be deposited and planarized by chemical mechanical polishing.

[0040] Contacts 66 can be formed that completely penetrate the dielectric layers 60, 62, 64 to land on the heavily doped region 41. Contacts 68 can be formed that completely penetrate the dielectric layers 60, 62, 64 to land on the heavily doped region 43. The heavily doped region 41 electrically couples the contact 66 to the doped region 40 with a reduced contact resistance. The heavily doped region 43 electrically couples the contact 68 to the doped region 42 with a reduced contact resistance. The contacts 66, 68 can be composed of a metal (such as tungsten). The doped regions 40, 42 can be biased through the contacts 66, 68, and the contacts 66, 68 can be coupled to interconnects (not shown) in a dielectric layer formed over the dielectric layer 64.

[0041] In use, light (such as a laser) received from the waveguide core 11 propagates in the waveguide structure including the waveguide cores 12, 13 and the waveguide core segments 20 towards the photodetector 14 and is transmitted from the waveguide structure to the semiconductor layer 26 of the photodetector 14. The waveguide structure can support the propagation of light with transverse electric polarization, transverse magnetic polarization, or a combination of both polarizations. In one embodiment, the light received by the photodetector 14 from the waveguide structure can be modulated into an optical signal. The semiconductor layer 26 absorbs the photons of the light and converts the absorbed photons into charge carriers through photoelectric conversion. The biasing of the doped regions 40, 42 causes the charge carriers to be collected and output from the photodetector 14 to provide a measurable photocurrent (as a function of time).

[0042] A waveguide structure including waveguide cores 12, 13 and waveguide core segments 20 can significantly improve the performance metrics of the photodetector 14, such as responsivity, coupling efficiency, and / or bandwidth. The performance metrics of the photodetector 14 can be improved by the waveguide structure without modifying the shape and / or size of the semiconductor layer 26. The waveguide structure can reduce the footprint of the photodetector 14 while maintaining satisfactory performance metrics.

[0043] Reference Figure 6 And according to an alternative embodiment, the length of the waveguide core segment 20 can vary along the length of the waveguide structure. In one embodiment, one or more waveguide core segments 20 may lack the protruding ends at the outer sidewalls 75, 77 of the waveguide cores 12, 13 and may include only a bridging portion spanning the gap G1 between the inner sidewalls 74, 76 of the waveguide cores 12, 13. In one embodiment, one or more waveguide core segments 20 lacking the protruding ends may alternate along the length of the waveguide structure with waveguide core segments 20 including the protruding ends.

[0044] Reference Figure 7 And according to an alternative embodiment, one or more waveguide core segments 20 may be disposed within the gap G1 between the inner sidewall 74 of the waveguide core 12 and the inner sidewall 76 of the waveguide core 13 without bridging the gap G1 between the waveguide cores 12 and 13. In one embodiment, one or more non-bridging waveguide core segments 20 may alternate along the length of the waveguide structure with waveguide core segments 20 including the bridging portion.

[0045] Reference Figure 8 、 Figure 8A , according to an alternative embodiment, the structure 10 can be modified such that the photodetector 14 has a vertical arrangement instead of a lateral arrangement. Specifically, as Figure 8 shown, the doped region 40 can extend throughout the spacer 24, the heavily doped region 41 can be disposed in the spacers 24 on both sides of the semiconductor layer 26, and the doped region 42 and the heavily doped region 43 can be disposed in the upper portion of the semiconductor layer 26. In an alternative embodiment, as Figure 8A shown, the structure 10 can be configured such that the heavily doped region 41 is disposed in the spacer 24 adjacent to only one side of the semiconductor layer 26.

[0046] In an alternative embodiment, the semiconductor layer 26 can be entirely disposed on and above the top surface 28 of the spacer 24. In an alternative embodiment, the photodetector 14 can be configured as an avalanche photodetector, which includes an intrinsic semiconductor material region (defining a multiplication region) in the spacer 24 and an additional doped region (defining a charge control region) in the spacer 24.

[0047] Reference Figure 9And according to an alternative embodiment, the structure 10 may further include a waveguide structure having waveguide cores 52, 54, and waveguide core segments 56. The waveguide cores 52, 54 are similar or identical to the waveguide cores 12, 13, and the waveguide core segments 56 are similar to the waveguide core segments 20. The waveguide core 52 is disposed near the waveguide core 54, where a groove or gap G3 separates the waveguide core 52 from the waveguide core 54. The waveguide cores 52 and 54 may extend longitudinally along their respective longitudinal axes 51, 53. The longitudinal axes 51, 53 of the waveguide cores 52, 54 may be parallel and aligned with the longitudinal axis 36 of the semiconductor layer 26, and the longitudinal axes 51, 53 of the waveguide cores 52, 54 may be parallel and aligned with the longitudinal axes 15, 17 of the waveguide cores 12, 13.

[0048] The waveguide core segments 56 of the waveguide structure are spaced apart along the longitudinal axis 51 of the waveguide core 52 and the longitudinal axis 53 of the waveguide core 54. In one embodiment, the waveguide core segments 56 may be oriented longitudinally transverse to the longitudinal axes 53, 55 of the waveguide cores 52, 54. In one embodiment, each waveguide core segment 56 may include a portion bridging across the gap G3 between the inner sidewalls of the waveguide core 52 and the waveguide core 54, a protruding end portion protruding outward from the outer sidewall of the waveguide core 52, and a protruding end portion protruding outward from the outer sidewall of the waveguide core 54.

[0049] The waveguide structure including the waveguide cores 52, 54, and waveguide core segments 56 abuts (i.e., shares a boundary) the side edge 25 of the spacer 24. In one embodiment, the waveguide cores 52 and 54 of the waveguide structure may abut the side edge 25 of the spacer 24. In a representative embodiment, the protruding end portion and the bridging portion of one of the waveguide core segments 56 may also abut the side edge 25 of the spacer 24.

[0050] The waveguide structure including the waveguide cores 52, 54, and waveguide core segments 56 has an envelope at the opposite edges of the protruding end portions of the waveguide core segments 56. In a representative embodiment, the envelope of the waveguide structure may have a constant effective width dimension. In an alternative embodiment, the envelope of the waveguide structure may have a tapered effective width dimension. In an alternative embodiment, the width dimension of the envelope may increase linearly or non-linearly as the distance from the side edge 25 of the spacer 24 decreases.

[0051] The waveguide core segments 56 are characterized by a pitch and a width, and adjacent pairs of waveguide core segments 56 are separated by a gap G4. In one embodiment, the waveguide core segments 56 may have a uniform pitch and gap G4. In an alternative embodiment, the uniform pitch and gap G4 of the waveguide core segments 56 may vary with the position relative to the side 23 of the spacer 24. In an alternative embodiment, the width of the waveguide core segments 56 may vary with the position relative to the side 23 of the spacer 24. In an alternative embodiment, the sidewalls of the bridging portions of the waveguide core segments 56 may have a curvature, and the protruding ends of the waveguide core segments 56 may be rounded. In one embodiment, the period of the waveguide core segments 20 may be equal to half the wavelength of the light received by the structure 10, or an integer multiple of half the wavelength, and the period of the waveguide core segments 56 may be equal to a quarter of the wavelength of the light received by the structure 10, or an integer multiple of a quarter of the wavelength.

[0052] The waveguide structure including the waveguide cores 52, 54 and the waveguide core segments 56 may be formed simultaneously with the waveguide cores 11, 13 and the waveguide core segments 20. The waveguide structure may be composed of the same material as the waveguide cores 11, 13 and the waveguide core segments 20.

[0053] The pitch, width and / or size of the gap G4 of the waveguide core segments 56 may be different from the pitch, width and / or size of the gap G2 of the waveguide core segments 20. Specifically, the size and position of the waveguide core segments 56 and the gap G4 may have a pitch such that the waveguide core segments 56 are configured to reflect light of a given operating wavelength in opposite directions. The light that reaches and is not absorbed by the semiconductor layer 26 of the photodetector 14 and passes through the semiconductor layer 26 may be reflected back to the semiconductor layer 26 by the waveguide structure including the waveguide cores 52, 54 and the waveguide core segments 56 and absorbed by the semiconductor layer 26, which may contribute to bandwidth improvement and reduce the footprint of the photodetector 14.

[0054] Reference Figure 10 According to an alternative embodiment, the waveguide structure including the waveguide cores 12, 13 and the waveguide core segments 20 may further include waveguide cores 72 disposed above the waveguide core 12 in height, waveguide cores 73 disposed above the waveguide core 13 in height, and waveguide core segments 70 disposed above the waveguide core segments 20 in height. In one embodiment, the waveguide core segments 70 and the waveguide cores 72, 73 may be composed of a material different from that of the waveguide core segments 20 and the waveguide cores 12, 13. In one embodiment, the waveguide core segments 70 and the waveguide cores 72, 73 may be composed of a dielectric material (such as silicon nitride). In an alternative embodiment, the waveguide core segments 70 and the waveguide cores 72, 73 may be composed of a semiconductor material (such as polysilicon).

[0055] In one embodiment, waveguide core 72 can be narrower than waveguide core 12 and be located at the center above waveguide core 12, waveguide core 73 can be narrower than waveguide core 12 and be located at the center above waveguide core 13, and waveguide core segment 20 can be narrower than waveguide core segment 20 and be located at the center above waveguide core segment 20. Waveguide cores 72, 73, and waveguide core segment 70 can serve to improve the mode match between light and photodetector 14.

[0056] Reference Figure 11 And according to an alternative embodiment, waveguide core 11 can include a tapered section 58 that is laterally disposed near a waveguide structure that includes waveguide cores 12, 13, and waveguide core segment 20. The waveguide structure can be terminated at an end of side 23 away from spacer 24 by one of waveguide core segments 20. The tapered section 58 of waveguide core 11 can be configured to effect evanescent coupling through a gap between the tapered section 58 and the waveguide structure, thereby enabling lateral transmission of light. For example, factors such as the tapering of the tapered section 58 of waveguide core 11 and the size of the gap can effect evanescent coupling of light. The tapered section 58 of waveguide core 11 can have an effective width dimension that tapers towards the terminal. In an alternative embodiment, the tapered section 58 can be tapered such that its effective width dimension varies linearly or non-linearly as the distance from the terminal decreases. Waveguide core 11 can include a bend (not shown) that guides waveguide core 11 such that the tapered section 58 is disposed near the waveguide structure.

[0057] The above method is used to fabricate integrated circuit chips. The manufacturer can distribute the resulting integrated circuit chips in the form of a raw wafer (e.g., a single wafer having multiple unpackaged chips), a bare die, or a packaged form. The chips can be integrated with other chips, discrete circuit elements, and / or other signal processing devices as part of an intermediate or final product. The final product can be any product that includes an integrated circuit chip, such as a computer product or a smart phone having a central processing unit.

[0058] Terms recited herein that are modified by approximating language such as “about,” “substantially,” and “essentially” are not limited to the specified exact value. The approximating language can correspond to the precision of the instrument used to measure the value and, unless otherwise relying on the precision of the instrument, can represent + / −10% of the recited value.

[0059] In this document, terms such as "vertical", "horizontal", etc. are used as examples to establish a reference frame and are not restrictive. The term "horizontal" as used herein is defined as a plane parallel to the conventional plane of a semiconductor substrate, regardless of its actual three-dimensional spatial orientation. The terms "vertical" and "orthogonal" refer to directions perpendicular to the horizontal plane as just defined. The term "lateral" refers to a direction in the reference frame within that horizontal plane.

[0060] A feature "connected" or "coupled" to another feature may be directly connected or coupled to that other feature, or there may be one or more intermediate features. If there are no intermediate features, the feature may be "directly connected" or "directly coupled" to the other feature. If there is at least one intermediate feature, the feature may be "indirectly connected" or "indirectly coupled" to the other feature. A feature "on" or "in contact with" another feature may be directly on or in direct contact with that other feature, or there may be one or more intermediate features. If there are no intermediate features, the feature may be directly "on" or "in direct contact with" the other feature. If there is at least one intermediate feature, the feature may be "indirectly" "on" or "in indirect contact with" the other feature. If one feature extends over and covers a portion of another feature, the different features may "overlap".

[0061] The descriptions of the various embodiments of the present invention are for illustrative purposes only and are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terms used herein are chosen to best explain the principles of the embodiments, practical applications, or technical improvements over technologies known in the market, or to enable those of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A structure for a photonic chip, characterized in that, The structure includes: A photodetector, including a spacer and a semiconductor layer on the spacer, the spacer including a first side; and A first waveguide structure, including a first waveguide core, a second waveguide core, a first slot between the first waveguide core and the second waveguide core, and a first plurality of waveguide core segments, the first waveguide structure adjacent to the first side of the spacer, the first side of the spacer adjacent to the semiconductor layer, and each of the first plurality of waveguide core segments including a first portion disposed in the first slot.

2. The structure according to claim 1, wherein The semiconductor layer has a longitudinal axis, and the first slot is centered along the first side relative to the longitudinal axis of the semiconductor layer.

3. The structure according to claim 1, characterized in that, The spacer includes a second side opposite to the first side, and further includes: A second waveguide structure, including a third waveguide core, a fourth waveguide core, a second slot between the third waveguide core and the fourth waveguide core, and a second plurality of waveguide core segments, the second waveguide structure adjacent to the second side of the spacer, the second side of the spacer adjacent to the semiconductor layer, and the second plurality of waveguide core segments extending from the third waveguide core across the second slot to the fourth waveguide core.

4. The structure according to claim 3, wherein, The semiconductor layer is configured to absorb light having a wavelength, and the second plurality of waveguide core segments have a first period equal to a quarter of the wavelength or an integer multiple of a quarter of the wavelength.

5. The structure according to claim 4, wherein The first plurality of waveguide core segments have a second period equal to a half of the wavelength or an integer multiple of a half of the wavelength.

6. The structure according to claim 1, wherein The semiconductor layer is configured to absorb light having a wavelength, and the first plurality of waveguide core segments have a period equal to a half of the wavelength or an integer multiple of a half of the wavelength.

7. The structure according to claim 1, wherein The first waveguide structure further includes a third waveguide core disposed above the first waveguide core in height, a fourth waveguide core disposed above the second waveguide core in height, and a second plurality of waveguide core segments disposed above the first plurality of waveguide core segments in height.

8. The structure according to claim 7, wherein, The first waveguide core, the second waveguide core, and the first plurality of waveguide core segments include a first material, and the third waveguide core, the fourth waveguide core, and the second plurality of waveguide core segments include a second material different from the first material.

9. The structure according to claim 8, wherein The first material is single-crystalline silicon, and the second material is silicon nitride or polycrystalline silicon.

10. The structure according to claim 1, wherein The semiconductor layer includes germanium.

11. The structure according to claim 1, characterized in that, Further included is: A first doped region in the spacer, the first doped region having a first conductivity type; And A second doped region in the spacer, the second doped region having a second conductivity type opposite to the first conductivity type, wherein the semiconductor layer is disposed on a portion of the spacer between the first doped region and the second doped region, and the portion of the spacer includes intrinsic semiconductor material.

12. The structure according to claim 1, wherein, The first plurality of waveguide core segments are separated by a plurality of gaps, and the sizes and positions of the first plurality of waveguide core segments and the plurality of gaps are designed to define a sub-wavelength grating.

13. The structure according to claim 12, wherein The plurality of gaps are filled with portions of a dielectric material to define a metamaterial.

14. The structure according to claim 1, wherein Further included is: A third waveguide core, including a tapered section arranged adjacent to the first waveguide core of the first waveguide structure, there being a gap between the tapered section of the third waveguide core and the first waveguide structure, and the tapered section of the third waveguide core configured to transmit light to the first waveguide structure.

15. The structure according to claim 1, characterized in that, The first waveguide core has a first longitudinal axis, the second waveguide core has a second longitudinal axis, and each of the first plurality of waveguide core segments is laterally aligned with the first longitudinal axis and laterally aligned with the second longitudinal axis along a length direction.

16. The structure according to claim 1, wherein The first waveguide core has a first sidewall that abuts the first groove and a second sidewall opposite the first sidewall, and each of the first plurality of waveguide core segments has a second portion that protrudes outward from the second sidewall of the first waveguide core.

17. The structure according to claim 16, wherein, The second waveguide core has a first sidewall that abuts the first groove and a second sidewall opposite the first sidewall, and each of the first plurality of waveguide core segments has a third portion that protrudes outward from the second sidewall of the second waveguide core.

18. The structure according to claim 17, characterized in that, The first portion of each of the first plurality of waveguide core segments extends from the first waveguide core across the first groove to the second waveguide core.

19. The structure according to claim 1, wherein, The first portion of each of the first plurality of waveguide core segments extends from the first waveguide core across the first groove to the second waveguide core.

20. A method for forming a structure of a photonic chip, characterized in that, The method includes: forming a photodetector including a spacer and a semiconductor layer on the spacer; and forming a waveguide structure including a first waveguide core, a second waveguide core, a groove between the first waveguide core and the second waveguide core, and a plurality of waveguide core segments, wherein the waveguide structure abuts a side edge of the spacer, the side edge of the spacer is adjacent to the semiconductor layer, and each of the plurality of waveguide core segments includes a portion disposed in the groove.

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