Single photon avalanche photodiode and method of manufacturing the same

Abstract

A single photon avalanche photodiode and a method of manufacturing the same are provided. The single photon avalanche photodiode includes a substrate, a waveguide region, an active region, a depletion region, a contact layer, and a first electrode and a second electrode. The waveguide region on the substrate includes a first portion extending along a first direction and a second portion extending along a second direction, the first direction intersecting the second direction; the active region on the waveguide region extends along the first portion of the waveguide region; the depletion region is on the active region; the contact layer is on the depletion region; the first electrode is on the contact layer, and the second electrode is on the waveguide region. The single photon avalanche photodiode is configured to transmit light incident along the first direction through the waveguide region to the active region to generate photo-generated carriers, and transmit the photo-generated carriers to the depletion region.

Description

Technical Field

[0001] This application relates to the field of semiconductor photodetector technology, and more specifically to a single-photon avalanche photodiode and its manufacturing method. Background Technology

[0002] With the rapid development of information industries such as quantum technology and deep space exploration, single-photon detectors (SPDs) operating in the near-infrared (NIR) band have received widespread attention in fields such as quantum secure communication and eye-safe laser detection and ranking (LiDAR). Among various near-infrared single-photon detectors, single-photon avalanche photodiodes (SPADs) based on the semiconductor avalanche effect have become one of the core single-photon detection devices due to their high sensitivity and cost advantages. However, due to limitations in device structure, SPADs still face technical bottlenecks where improving quantum efficiency and reducing dark carrier numbers are mutually restrictive, making it difficult to meet the performance requirements of quantum communication systems and laser ranging systems. Summary of the Invention

[0003] In view of the above problems, this application provides a single-photon avalanche photodiode and a method for manufacturing the same.

[0004] According to a first aspect of the embodiments of this application, a single-photon avalanche photodiode is provided. The single-photon avalanche photodiode includes a substrate, a waveguide region, an active region, a depletion region, a contact layer, and a first electrode and a second electrode. The waveguide region on the substrate includes a first portion extending along a first direction and a second portion extending along a second direction, the first and second directions intersecting; the active region on the waveguide region extends along the first portion of the waveguide region; the depletion region is located on the active region; the contact layer is located on the depletion region; the first electrode is located on the contact layer; and the second electrode is located on the waveguide region. The single-photon avalanche photodiode is configured to transmit light incident along the first direction through the waveguide region to the active region to generate photogenerated carriers, and to transmit the photogenerated carriers to the depletion region.

[0005] According to an embodiment of this application, the end of the depletion region is recessed relative to the end of the active region in a first direction.

[0006] According to an embodiment of this application, the waveguide region includes a diluted waveguide region and an optical matching layer on the diluted waveguide region, wherein the end of the optical matching layer is recessed relative to the end of the diluted waveguide region in a first direction; the active region is on the optical matching layer, and the end of the active region is recessed relative to the end of the optical matching layer in the first direction.

[0007] According to an embodiment of this application, the depletion region includes an etch barrier layer on the active region and an intrinsic layer on the etch barrier layer, wherein the end of the contact layer is recessed relative to the end of the intrinsic layer in a first direction, and the end of the intrinsic layer is recessed relative to the end of the etch barrier layer in the first direction.

[0008] According to an embodiment of this application, the active layer includes an absorption layer, a gradient layer, a charge layer and a multiplication layer stacked sequentially on the waveguide region, wherein the thickness of the absorption layer in the vertical direction is 400 nm to 1 μm.

[0009] According to a second aspect of the present application, a method for manufacturing a single-photon avalanche photodiode is provided. The method includes: forming an epitaxial layer on a substrate, the epitaxial layer including an epitaxial waveguide layer on the substrate, an epitaxial active layer on the epitaxial waveguide layer, an epitaxial depletion layer on the epitaxial active layer, and an epitaxial contact layer on the epitaxial depletion layer; etching the epitaxial contact layer and the epitaxial depletion layer to expose the epitaxial active layer to form a contact layer and a depletion region; etching the epitaxial active layer to expose the waveguide epitaxial layer to form an active region; etching the epitaxial waveguide layer to expose the substrate to form a waveguide region, the waveguide region including a first portion extending along a first direction and a second portion extending along a second direction, the first direction intersecting the second direction; forming a first electrode on the contact layer and a second electrode on the waveguide region. The single-photon avalanche photodiode is configured to transmit light incident along the first direction through the waveguide region to the active region to generate photogenerated carriers and to transmit the photogenerated carriers to the depletion region.

[0010] According to an embodiment of this application, etching an epitaxial active layer to expose a waveguide epitaxial layer to form an active region includes: forming a first mask on the epitaxial active layer; and etching the epitaxial active layer based on a pattern of the first mask to form an active region, such that the end of the depletion region is recessed relative to the end of the active region in a first direction.

[0011] According to an embodiment of this application, etching an epitaxial waveguide layer to an exposed substrate to form a waveguide region includes: forming a second mask on the epitaxial waveguide layer; and etching the epitaxial waveguide layer based on a pattern of the second mask to form a waveguide region such that, in a first direction, the end of the active region is recessed relative to the end of the waveguide region.

[0012] According to an embodiment of this application, the waveguide region includes a diluted waveguide region and an optical matching layer on the diluted waveguide region. The method further includes: forming a third mask on the waveguide region; and etching a portion of the optical matching layer in a first direction based on the pattern of the third mask, such that in the first direction, the end of the retained optical matching layer is recessed relative to the end of the diluted waveguide layer.

[0013] According to an embodiment of this application, the epitaxial depletion layer includes an etch stop layer on the epitaxial active layer and an intrinsic layer on the etch stop layer. Etching the epitaxial contact layer and the epitaxial depletion layer to expose the epitaxial active layer to form a contact layer and a depletion region includes: performing stepwise etching of the etch stop layer, the intrinsic layer, and the epitaxial contact layer such that, in a first direction, the end of the etched contact layer is recessed relative to the end of the etched intrinsic layer, and the end of the etched intrinsic layer is recessed relative to the end of the etched etch stop layer.

[0014] According to an embodiment of this application, a single-photon avalanche photodiode is provided. Unlike a vertically incident single-photon avalanche photodiode, incident light can couple from a first portion of the waveguide region of the device into an active region extending along the first portion along a first direction. The generated photogenerated carriers undergo avalanche multiplication and are transported to the depletion region. This can improve quantum efficiency by increasing the length of the active region in the first direction without increasing the thickness of the active region, alleviating the problem of dark carrier surge caused by a thicker active region, and at least partially solving the contradiction between improving quantum efficiency and reducing dark carrier count. Attached Figure Description

[0015] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, which will be explained below in conjunction with the drawings:

[0016] Figure 1A A schematic cross-sectional view of a single-photon avalanche photodiode according to an embodiment of this application is shown along a first direction;

[0017] Figure 1B A schematic cross-sectional view of a single-photon avalanche photodiode according to an embodiment of this application is shown along a second direction;

[0018] Figure 1C A perspective view of a single-photon avalanche photodiode according to an embodiment of this application is shown schematically.

[0019] Figure 2 A flowchart illustrating a method for manufacturing a single-photon avalanche photodiode according to an embodiment of this application is shown schematically.

[0020] Figures 3A to 8A The illustration schematically shows a cross-sectional view along a first direction of some stages in a method for manufacturing a single-photon avalanche photodiode according to an embodiment of this application;

[0021] Figures 3B to 8B The illustration schematically shows a cross-sectional view along a second direction of some stages in a method for manufacturing a single-photon avalanche photodiode according to an embodiment of this application;

[0022] Figures 5C to 8CThe illustration schematically shows perspective views of some stages in a method for manufacturing a single-photon avalanche photodiode according to an embodiment of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0024] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this application.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0026] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0027] In the description of this application, it should be understood that the terms "longitudinal", "length", "circumferential", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the subsystem or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0028] Similarly, to simplify this application and aid in understanding one or more of the various disclosed aspects, in the above description of exemplary embodiments of this application, various features of this application are sometimes grouped together into a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0029] With the rapid development of information industries such as quantum technology and deep space exploration, single-photon detectors (SPDs) operating in the near-infrared (NIR) band have received widespread attention in fields such as quantum secure communication and eye-safe laser ranging (LiDAR). Among various near-infrared SPDs, InGaAs / InP-based solid-state SPDs have become core detection devices in quantum communication systems and long-distance laser ranging systems due to their superior overall performance, controllable cost, high reliability, ease of use, compact structure, and lack of need for cryogenic cooling. Their single-photon-level detection sensitivity and GHz-level gating switching frequency can improve the key generation rate of quantum communication systems and extend the maximum detection distance of laser ranging systems. The continuous growth in data transmission capacity of communication systems, the increasing demands on the sensitivity of detection systems, and the higher requirements for the transmission rate, power consumption, and integration of single-photon detectors are all driving the evolution of InGaAs / InP-based SPDs towards monolithic photonic integrated chips.

[0030] In related technologies, InGaAs / InP-based SPD devices utilize vertically incident multilayer structures constructed from materials such as InP, InGaAs, and InGaAsP. However, vertically incident multilayer structures have inherent structural defects. On one hand, the number of dark carriers generated by thermal excitation inside the device is positively correlated with the thickness of the absorption layer. In the technical path of improving quantum efficiency by thickening the absorption layer, the dark count rate and dark current increase synchronously with the increase of the absorption layer thickness, leading to a deterioration in the device's signal-to-noise ratio. On the other hand, the photosensitive areas of the depletion region and the active region of the vertically incident multilayer structure are the same. If the junction capacitance is reduced and the RC time constant is shortened to improve the device response speed by reducing the photosensitive area, the detection sensitivity will decrease due to the reduction in photosensitive area, thus limiting the optimization effect of the device response speed.

[0031] Therefore, as one of the core single-photon detection devices, the single-photon avalanche photodiode (SPAD) based on the semiconductor avalanche effect still faces technical bottlenecks due to the inherent limitations of the device structure. These bottlenecks involve a trade-off between improving quantum efficiency and reducing the number of dark carriers, making it difficult to meet the performance requirements of current quantum communication systems and laser ranging systems.

[0032] In view of this, embodiments of this application provide a single-photon avalanche photodiode and its manufacturing method, which can realize monolithic integration of single-photon detectors and has high detection efficiency and low dark count, etc.

[0033] Figure 1A A schematic cross-sectional view of a single-photon avalanche photodiode according to an embodiment of this application is shown along a first direction; Figure 1B A schematic cross-sectional view of a single-photon avalanche photodiode according to an embodiment of this application is shown along a second direction; Figure 1C A perspective view of a single-photon avalanche photodiode according to an embodiment of this application is schematically shown. It should be noted that... Figure 1C The X-axis is defined as the first direction X-X', the Y-axis as the second direction Y-Y' intersecting the first direction X-X', and the Z-axis as the vertical direction. In one embodiment of this application, the first direction X-X' and the second direction Y-Y' may be perpendicular to each other in the same horizontal plane, and the vertical direction may be perpendicular to the horizontal plane. It should be understood that the perspective views in this application are only used to show the structural schematic of the device from the direction of each axis; for specific structure, please refer to the cross-sectional views. For ease of description, Figures 1A-1C Only the structures of the waveguide region, active region, and depletion region are shown. Figure 1A The arrows in the diagram indicate the direction of light transport. Figure 1A The diagram only shows the transport direction of light from one side; the embodiments of this application also apply to the incident light from both sides.

[0034] like Figures 1A-1C As shown, the single-photon avalanche photodiode of this embodiment may include a substrate 1, a waveguide region, an active region, a depletion region, a contact layer 11, a first electrode 12, and a second electrode 13. The photodiode can be configured to transmit incident light along a first direction through the waveguide region to the active region to generate photogenerated carriers, and to transmit the photogenerated carriers to the depletion layer.

[0035] Substrate 1 may include a semi-insulating InP substrate, which can be formed by Fe doping or other treatments on the InP material to reduce series resistance and stray capacitance. The single-photon avalanche photodiode of this embodiment may also include a buffer layer 2 between the substrate 1 and the waveguide region to reduce lattice mismatch in the epitaxial material. Buffer layer 2 may include InP, and buffer layer 2 may be lightly N-type doped with a doping concentration of 1 × 10⁻⁶. 15 cm －3 .

[0036] refer to Figure 1C The waveguide region on substrate 1 may include a first portion W1 extending along a first direction and a second portion W2 extending along a second direction. The first direction may intersect with the second direction. The first direction may be... Figure 1C In the X-X' direction, the second direction can be Figure 1C The first portion W1 of the waveguide region can restrict the incident light to propagate along the first direction within the waveguide region, and the second portion W2 of the waveguide region can be used to expand the area in the second direction to achieve good contact with the second electrode 13. In an embodiment, the first portion W1 of the waveguide layer can be symmetrical with respect to the second portion W2 in the first direction, so that light can be incident on both sides of the waveguide region. In some embodiments, the waveguide region may include a diluted waveguide region 3 and an optical matching layer 4 on the diluted waveguide region 3, which can use evanescent wave coupling to transmit the incident light from the waveguide region to the active region. In the first direction, the end of the optical matching layer 4 can be recessed relative to the end of the diluted waveguide region 3, which allows the incident light to complete mode field constraint and smooth matching in the recessed region, reducing reflection and scattering caused by mode field mismatch, and improving the uniformity of light coupling into the active region.

[0037] The diluted waveguide region 3 can be a periodic structure with alternating stacked first refractive index layer 31 and second refractive index layer 32, wherein the first refractive index layer 31 and the second refractive index layer 32 have different refractive indices. For example, the first refractive index layer 31 may include InP, and its thickness may be 80 nm to 100 nm. The second refractive index layer 32 may include InGaAsP, and its thickness may be 50 nm to 70 nm. The first refractive index layer 31 and the second refractive index layer 32 may be lightly doped with N-type, for example, with a doping concentration of 1 × 10⁻⁶. 15 cm －3 The period of the periodic structure of the diluted waveguide region 3 can be set according to application requirements, and can be stacked, for example, 10 periods, which is not limited here.

[0038] The optical matching layer 4 may include a first optical matching layer 41 on the diluted waveguide region 3 and a second optical matching layer 42 on the first optical matching layer 41. It is used to modulate the refractive index distribution at the interface between the diluted waveguide region 3 and the active region, reducing interface reflection loss. Utilizing the beat-mode effect, it allows the optical signal to be coupled into the active region more efficiently, thereby improving the quantum efficiency of the device. The first optical matching layer 41 and the second optical matching layer 42 can be heavily N-type doped, with a doping concentration of 1 × 10⁻⁶. 18 cm －3 The first optical matching layer 41 and the second optical matching layer 42 may include InGaAsP, etc., and their thicknesses may differ. They are used to match and dilute the mode distribution of the waveguide region 3 and the active region. The thickness of the first optical matching layer 41 may be 700nm~900nm, and the thickness of the second optical matching layer 42 may be 100nm~300nm.

[0039] The active region on the waveguide region may extend along the first portion of the waveguide region. In some embodiments, due to fabrication process errors (e.g., etching process errors), the active region may include a protrusion corresponding to the second portion of the waveguide region in the second direction. The active region may be located on the optical matching layer 4 (second optical matching layer 42), and the end of the active region in the first direction may be recessed relative to the end of the optical matching layer 4 to form a transition region without an active region. The transition region can prevent incident light from directly entering the active region and causing reflection and scattering due to mode field abrupt changes, thereby improving the coupling efficiency of light entering the active region. In a specific embodiment, the active layer may include an absorption layer 5, a gradient layer 6, a charge layer 7, and a multiplication layer 8 sequentially stacked on the optical matching layer 4.

[0040] The absorption layer 5 absorbs incident light at the target wavelength and converts the optical signal into photogenerated carriers (e.g., electron-hole pairs). The absorption layer 5 may include InGaAs, which has a high absorption coefficient at the communication wavelength of 1550 nm. The absorption layer 5 may be lightly doped with N-type magnets, with a doping concentration of 2 × 10⁻⁶. 15 cm －3 The thickness of the absorption layer 5 in the vertical direction can be less than one micrometer, for example, 400 nm to 1 μm.

[0041] Compared to the micron-scale absorption layer in related technologies, the absorption layer extending along the first direction in this embodiment can absorb incident light and transport photogenerated carriers to the multiplication layer via evanescent wave coupling. This can improve quantum efficiency by increasing the length of the active region in the first direction without increasing the thickness of the active region.

[0042] The multiplication layer 8 can provide a strong electric field conducive to avalanche generation, enabling avalanche multiplication triggered by a single photogenerated carrier. The multiplication layer 8 may include InP, and its thickness may be 1.4 μm to 1.6 μm. The gradient layer 6 may include at least one layer of a gradient layer material, which may include indium gallium arsenide phosphide, such as In... 1-x Ga x As y P 1-y The molar percentage of constituent elements in each graded layer can be different, while the thickness of each graded layer can be the same, to achieve a gradual change in bandgap from the absorption layer 5 to the charge layer 7. This facilitates the crossing of photogenerated carriers across the valence band barrier at the interface of heterojunctions (e.g., a heterojunction of InGaAs and InP materials) and transports the photogenerated carriers to the multiplication layer 8. The charge layer 7 can be N-type doped, with a doping concentration of 5 × 10⁻⁶. 17 cm －3 It is used to separate the absorption layer 5 and the multiplication layer 8 to form a strong electric field in the multiplication layer 8. The charge layer 7 may include InP, etc., and the thickness of the charge layer 7 may be 140 nm to 160 nm, etc.

[0043] The depletion region can be located on the active region. In some embodiments, the end of the depletion region is recessed relative to the end of the active region, meaning the length of the depletion region in the first direction can be less than the length of the active region in the first direction. This difference in length between the depletion region and the active region in the first direction can be achieved using mesa etching. This difference in length between the depletion region and the active region in the first direction avoids the influence of the absorption layer length on the photosensitive area. The junction capacitance can be reduced by decreasing the photosensitive area of ​​the depletion region according to application requirements, thereby increasing the device operating frequency.

[0044] In some embodiments, the depletion region may include an etch stop layer 9 on the multiplication layer 8 and an intrinsic layer 10 on the etch stop layer 9. The etch stop layer 9 may be p-type doped, with a doping concentration of 5 × 10⁻⁶. 17 cm －3 The etch barrier layer 9 may include InP, etc., and its thickness may be 40 nm to 60 nm. The intrinsic layer 10 may be undoped, or the intrinsic layer 10 may be lightly doped with a low concentration of P-type, with a doping concentration of 2 × 10⁻⁶. 15 cm －3 The intrinsic layer 10 may include InP, etc., and its thickness may be 500nm~700nm.

[0045] Contact layer 11 can be located on intrinsic layer 10. Contact layer 11 can be heavily p-doped, with a doping concentration of 1 × 10⁻⁶. 18 cm －3The doping concentration of the contact layer 11 can be increased by multiple doping methods. A higher doping concentration on the contact surface can reduce the ohmic contact series resistance. The contact layer 11 may include InP, and its thickness can be 100 nm to 300 nm. In a first direction, the end of the contact layer 11 may be recessed relative to the end of the intrinsic layer 10; in a first direction, the end of the intrinsic layer 10 may be recessed relative to the end of the etch stop layer 9. Decreasing the lengths of the contact layer 11, the intrinsic layer 10, and the etch stop layer 9 in the first direction can avoid premature breakdown caused by edge electric field concentration at highly doped interfaces.

[0046] The first electrode 12 can be located on the contact layer 11. The second electrode 13 can be located on the optical matching layer 4, which can serve as the N-type contact layer of the second electrode. The first electrode 12 can be a Ti / Pt / Au metal electrode, etc., and the second electrode 13 can be an AuGeNi / Au metal electrode, etc.

[0047] According to an embodiment of this application, a single-photon avalanche photodiode is provided. Unlike a vertically incident single-photon avalanche photodiode, incident light can couple from a first portion of the waveguide region of the device into an active region extending along the first portion along a first direction. The generated photogenerated carriers undergo avalanche multiplication and are transported to the depletion region. This can improve quantum efficiency by increasing the length of the active region in the first direction without increasing the thickness of the active region, alleviating the problem of dark carrier surge caused by a thicker active region, and at least partially solving the contradiction between improving quantum efficiency and reducing dark carrier count.

[0048] In some embodiments, the single-photon avalanche photodiode of this application may further include a dielectric layer located on a substrate and coplanar waveguide electrodes. The dielectric layer may serve as a passivation layer covering the device surface, providing electrical isolation. The coplanar waveguide electrodes may be connected to the first electrode and the second electrode to extract signals. It should be noted that... Figures 1A-1C The dielectric layer and coplanar waveguide electrodes are not shown in the diagram. The manufacturing process of the single-photon avalanche photodiode in this embodiment will be further described below.

[0049] Figure 2 A flowchart illustrating a method for manufacturing a single-photon avalanche photodiode according to an embodiment of this application is shown schematically.

[0050] like Figure 2 As shown, the manufacturing method of this embodiment may include operations S210 to S250.

[0051] In operation S210, an epitaxial layer is formed on the substrate. The epitaxial layer includes an epitaxial waveguide layer on the substrate, an epitaxial active layer on the epitaxial waveguide layer, an epitaxial depletion layer on the epitaxial active layer, and an epitaxial contact layer on the epitaxial depletion layer.

[0052] In operation S220, the epitaxial contact layer and epitaxial depletion layer are etched to expose the epitaxial active layer to form the contact layer and depletion region.

[0053] In operation S230, the epitaxial active layer is etched down to expose the waveguide epitaxial layer to form the active region.

[0054] In operation S240, the epitaxial waveguide layer is etched down to the exposed substrate to form the waveguide region.

[0055] The waveguide region may include a first portion extending along a first direction and a second portion extending along a second direction. The first direction intersects with the second direction.

[0056] In operation S250, a first electrode is formed on the contact layer and a second electrode is formed on the waveguide region.

[0057] To better understand the manufacturing method of the single-photon avalanche photodiode of this application, the following are cross-sectional views of various directions in the manufacturing process of the single-photon avalanche photodiode according to the embodiments of this application. Figure 1A and Figures 3A to 8A , Figure 1B and Figures 3B to 8B as well as Figure 1C and Figures 5C to 8C The content of the embodiments of this application will be described below.

[0058] Figures 3A to 8C The diagrams schematically illustrate some stages of the method for manufacturing a single-photon avalanche photodiode according to embodiments of this application. It should be noted that in the various figures shown in this application, when the numbers in the titles of multiple figures are the same, the manufacturing processes corresponding to those figures are the same. When the numbers in the titles of multiple figures are the same but the letters are different, the manufacturing processes corresponding to those figures are the same, but the axial directions corresponding to those figures are different. For example, Figure 5C Is with Figure 5A and Figure 5B The corresponding perspective view, Figure 5A and Figure 5B These are cross-sectional views from two directions representing the same manufacturing process. In a specific embodiment, Figure 1A and Figures 3A to 8A This is a cross-sectional view along the first direction during the manufacturing process of a single-photon avalanche photodiode. Figure 1B and Figures 3B to 8B This is a cross-sectional view along the second direction during the manufacturing process of a single-photon avalanche photodiode. Figure 1C and Figures 5C to 8C This is a perspective view of the process of manufacturing a single-photon avalanche photodiodes.

[0059] like Figure 3A and 3BAs shown, an epitaxial layer can be formed on substrate 1. Substrate 1 can be a Fe-doped semi-insulating InP substrate. The epitaxial layer can be formed on substrate 1 after pretreatment operations such as cleaning using an epitaxial growth process. In this embodiment, a buffer layer 2 can be grown on substrate 1 using MOCVD (Metal-Organic-Chemical Vapor Deposition) to reduce lattice mismatch between the epitaxial layer and substrate 1. The buffer layer 2 can be lightly N-type doped, with a doping concentration of 1 × 10⁻⁶. 15 cm －3 Buffer layer 2 may include InP, etc., and its thickness may be 300 nm.

[0060] The epitaxial layer may include an epitaxial waveguide layer, an epitaxial active layer, an epitaxial depletion layer, and an epitaxial contact layer. The epitaxial waveguide layer may include an epitaxial dilution waveguide layer and an epitaxial optical matching layer. The epitaxial active layer may include an epitaxial absorption layer, an epitaxial graded layer, an epitaxial charge layer, and an epitaxial multiplication layer. The epitaxial depletion layer may include an epitaxial etch barrier layer and an epitaxial intrinsic layer.

[0061] For example, an epitaxial diluted waveguide layer 3A can be grown on the buffer layer 2, for instance, by alternately growing a first refractive index layer 31 and a second refractive index layer 32 for 10 cycles. The first refractive index layer 31 and the second refractive index layer 32 can be lightly N-type doped, with a doping concentration of 1 × 10⁻⁶. 15 cm －3 The first refractive index layer 31 can be InP, with a thickness of 90 nm. The second refractive index layer 32 can be InGaAsP, with a thickness of 60 nm. The band-edge cutoff absorption wavelength of the first refractive index layer 31 can be 0.92 μm; the band-edge cutoff absorption wavelength of the second refractive index layer 32 can be 1.1 μm, for example, it can be represented as Q1.1.

[0062] An epitaxial optical matching layer 4A can be grown on the epitaxially diluted waveguide layer 3A, for example, a first optical matching layer 41 and a second optical matching layer 42 can be grown. The first optical matching layer 41 and the second optical matching layer 42 can be heavily N-type doped, with a doping concentration of 1 × 10⁻⁶. 18 cm －3 The first optical matching layer 41 can be Q1.1 InGaAsP with a thickness of 800 nm. The second optical matching layer 42 can be Q1.4 InGaAsP with a thickness of 200 nm. Q1.1 and Q1.4 can represent band-edge absorption wavelengths of 1.1 μm and 1.4 μm, respectively. The epitaxial optical matching layer 4A can couple light to the absorption layer and serve as an N-type electrode contact layer.

[0063] An epitaxial absorption layer 5A can be grown on the epitaxial optical matching layer 4A to absorb photons of the target wavelength to form photogenerated carriers and transport them to the depletion region. The epitaxial absorption layer 5A can be lightly doped with N-type, with a doping concentration of 2 × 10⁻⁶. 15 cm －3 The epitaxial absorber layer 5A may include InGaAs, and its thickness may be 400 nm.

[0064] An epitaxial graded layer 6A can be grown on the epitaxial absorber layer 5A. For example, multiple layers of graded layer material can be grown to achieve a gradient in the bandgap from the absorber layer to the charge layer. This facilitates the transport of photogenerated carrier holes across the valence band barrier at the heterojunction (InGaAs and InP materials) into the multiplication layer. The epitaxial graded layer 6A can be a multilayer stacked structure, such as a stacked structure of 5 layers of graded layer material. The graded layer material may include In… 1-x Ga x As y P 1-y The molar percentage of constituent elements in each gradient layer material can be designed according to actual application requirements. Its band-edge cutoff absorption wavelengths can be 1.4μm, 1.3μm, 1.2μm, 1.1μm, and 1.0μm respectively. Each gradient layer material can have a uniform thickness, for example, 20nm.

[0065] An epitaxial charge layer 7A can be grown on the epitaxial graded layer 6A. The epitaxial charge layer 7A can be heavily N-type doped, with a doping concentration of 5 × 10⁻⁶. 17 cm －3 The epitaxial charge layer 7A can be InP with a thickness of 90 nm. The epitaxial charge layer 7A can serve as an electric field control layer, controlling the electric field intensity in the absorption region to 1 × 10⁻⁶. 4 Within V / cm.

[0066] An epitaxial multiplication layer 8A can be grown on the epitaxial charge layer 7A. The epitaxial multiplication layer 8A can be lightly doped with N-type. The epitaxial multiplication layer 8A can be InP, with a thickness of 1.5 μm. The epitaxial multiplication layer 8A can provide a strong and uniform electric field, with an electric field strength reaching 4 × 10⁻⁶. 5 A value of V / cm or higher causes a single photogenerated carrier to trigger avalanche multiplication.

[0067] An epitaxial etch barrier layer 9A, an epitaxial intrinsic layer 10A, and an epitaxial contact layer 11A can be sequentially grown on the epitaxial multiplication layer 8A to define the size of the depletion region. The epitaxial etch barrier layer 9A may include p-type doped InP with a doping concentration of 1 × 10⁻⁶. 17 cm －3 The thickness can be 50 nm. The epitaxial intrinsic layer 10A may include p-type doped InP with a doping concentration of 2 × 10⁻⁶. 15cm －3 The thickness can be 600 nm. The epitaxial contact layer 11A may include p-type doped InP with a doping concentration of 1 × 10⁻⁶. 18 cm －3 The thickness can be 200nm.

[0068] In this embodiment, the epitaxial contact layer 11A can be p-type doped multiple times using a Zn3P2 source to increase its doping concentration. For example, the epitaxial layer can be ultrasonically cleaned by immersion in a stripping solution, acetone, and ethanol for 15 minutes respectively to remove impurities from the epitaxial layer surface; then, the surface can be rinsed with deionized water and dried at 100°C; subsequently, the epitaxial contact layer 11A can be doped using a closed-tube multiple diffusion method with zinc phosphide, at a diffusion temperature of 550°C and a diffusion time of 5 minutes. A higher doping concentration on the contact layer surface can reduce the ohmic contact series resistance.

[0069] like Figure 4A and 4B As shown, a lift-off pattern region for the first electrode, such as that for a P-type electrode, can be defined on the epitaxial contact layer 11A using photolithography. Ti / Pt / Au metal films are then formed on the lift-off pattern region using electron beam evaporation, with thicknesses of 20 nm, 40 nm, and 200 nm, respectively. After lift-off and cleaning, the first electrode 12 is formed.

[0070] The depletion region, active region, and waveguide region can be defined sequentially using the mesa etching method.

[0071] like Figures 5A-5C As shown, the depletion region can be defined. A dielectric film, such as silicon dioxide, can be deposited on the epitaxial contact layer 11A using plasma-enhanced chemical vapor deposition. The depletion region pattern of the first electrode 12 is defined using photolithography, and then the dielectric film outside the depletion region pattern is removed by etching with hydrofluoric acid solution to form a depletion region etch barrier mask. Based on the pattern of the depletion region etch barrier mask, the epitaxial contact layer 11A and the epitaxial depletion layer (epitaxy intrinsic layer 10A and epitaxial etch barrier layer 9A) can be etched sequentially using inductively coupled ion dry etching and wet etching methods (the etching solution can be a mixture of Br2 and methanol) until the epitaxial multiplication layer 8A is exposed to form the contact layer 11 and the depletion region. The depletion region may include the intrinsic layer 10 and the etch barrier layer 9.

[0072] In this embodiment, the etching gas for the ICP can be chlorine, methane, and hydrogen in a ratio of 2:2:1 (vacuum pressure 5 mtorr). The RF power can be 150W, and the ICP power can be 600W. The wet etching time can be 10 seconds to remove surface damage caused by dry etching.

[0073] In some embodiments, the epitaxial etch barrier layer 9A, the epitaxial intrinsic layer 10A, and the epitaxial contact layer 11A can be etched in stages, such that the end of the contact layer 11 after etching in the first direction is recessed relative to the end of the intrinsic layer 10 after etching, and the end of the intrinsic layer 10 after etching in the first direction is recessed relative to the end of the etch barrier layer 9, in order to avoid premature breakdown caused by edge electric field concentration at high doping concentration interfaces. In embodiments, in the second direction, the end of the contact layer 11 can also be recessed relative to the end of the intrinsic layer 10, and the end of the intrinsic layer 10 can also be recessed relative to the end of the etch barrier layer 9.

[0074] like Figures 6A-6C As shown, the depletion region etch block mask can be removed to define the active region. The active region mask pattern can be defined using photolithography, and the mask outside the active region mask pattern can be removed using a developer to form a first mask, such as a SiO2 mask. Based on the pattern of the first mask, the epitaxial active layer (epitaxy absorption layer 5A, epitaxial gradient layer 6A, epitaxial charge layer 7A, and epitaxial multiplication layer 8A) can be etched sequentially using ICP and wet etching methods until the epitaxial light matching layer 4A is exposed to form the active region. The active region includes the absorption layer 5, the gradient layer 6, the charge layer 7, and the multiplication layer 8.

[0075] In this embodiment, the etching gas for the ICP can be chlorine, methane, and hydrogen in a ratio of 2:2:1 (vacuum pressure 5 mtorr). The RF power can be 450 W, and the ICP power can be 1 kW. The wet etching time can be 30 seconds to remove surface damage caused by dry etching.

[0076] In the first direction, the end of the depletion region can be recessed relative to the end of the active region, that is, the length of the active region in the first direction can be greater than the length of the depletion region in the first direction. A mesa can be formed between the depletion region and the active region, which can avoid the influence of the absorption layer length on the photosensitive area. According to the application requirements, the junction capacitance of the device can be reduced and the operating frequency can be increased by reducing the photosensitive area of ​​the depletion region.

[0077] like Figures 7A-7C As shown, the first mask can be removed to define the waveguide region. The waveguide region mask pattern can be defined on the cleaned structure using photolithography, and a second mask, such as a SiO2 mask, can be developed. Based on the pattern of the second mask, the epitaxial waveguide layer (epitaxylectromagnetic matching layer 4A and epitaxial diluted waveguide layer 3A) can be etched using room-temperature wet etching until the substrate 1 is exposed to form the waveguide region. The waveguide region includes the diluted waveguide region 3 and the optical matching layer 4. In the first direction, the end of the active region can be recessed relative to the end of the waveguide region, i.e., the length of the first portion of the waveguide region can be greater than the length of the active region in the first direction.

[0078] In this embodiment, the etchant used for room-temperature wet etching is a mixed solution of H2SO4, H2O2, and H2O. The structure is then cleaned again after etching.

[0079] Return to reference Figures 1A-1C The second mask can be removed, and a dielectric film, such as silicon dioxide, can be regrown on the cleaned structure to passivate and protect the etched mesa structure. A photolithography method can be used to define the coupled waveguide region mask pattern, and a developer can be used to remove the mask outside the coupled waveguide region mask pattern to form a third mask. Based on the pattern of the third mask, a portion of the light matching layer 4 in the first direction can be etched sequentially using ICP and wet etching methods, such that the end of the light matching layer 4 retained in the first direction is recessed relative to the end of the diluted waveguide region 3.

[0080] Incident light can travel along the first direction ( Figure 1B The photogenerated carriers (in the horizontal direction within the paper) are transported from the dilute waveguide region 3 into the device, coupled to the absorption layer 5 through the optical matching layer 4, and then transported towards the depletion region.

[0081] Continue to refer to Figures 1A-1C A second electrode 13 can be formed, which can be an N-type electrode. The pattern of the second electrode 13 can be defined on a third mask on the photomatching layer 4 using photolithography, and the excess mask can be etched using HF solution to obtain N-type contact holes. After cleaning, a gold-germanium-nickel / gold (AuGeNi / Au) metal contact layer with a thickness of 100 / 400 nm can be fabricated using photolithographic lift-off. The second electrode 13 can be formed through an annealing process. The annealing temperature can be 400℃~600℃, and the annealing time can be 1h~1.5h. The annealing process provides good ohmic contact for both the P-type and N-type electrodes.

[0082] like Figures 8A-8C As shown, mesa planarization can be performed. For example, a dielectric layer 14 can be formed using spin coating. The dielectric layer 14 can be made of benzocyclobutene and has a thickness of 7 μm. Mesa planarization can be achieved by pre-baking at 90°C for 20 min and then curing at 280°C for 30 min. The top surface of the dielectric layer 14 can be substantially flush with the top surface of the first electrode 12. An opening 141 can be etched on the dielectric layer 14 using photolithography to expose the underlying second electrode 13, and a coplanar waveguide (CPW) electrode pattern can be defined again using photolithography. Based on the CPW electrode pattern, a CPW electrode 15 can be formed using electroplating gold. Electroplating allows the gold layer to uniformly rise along the opening 141 from the bottom second electrode 13 to the surface of the dielectric layer 14, thus solving the electrode connection problem caused by the difference in mesa height.

[0083] In this embodiment, the thickness of the substrate 1 can be reduced to 100 μm, and an antireflection film can be deposited on the sidewall of the diluted waveguide region 3 using magnetron sputtering. The antireflection film can be a TiOx film that enhances the transmission of incident light at a wavelength of 1550 nm.

[0084] According to embodiments of this application, the evanescent wave coupled single-photon avalanche photodiode is advantageous for heterogeneous integration and interconnection with photonic integrated circuits, and enables the realization of near-infrared indium gallium arsenide (IGaAs) single-photon avalanche photodiodes with InP waveguide heterogeneous integration for use in quantum optical applications. The single-photon avalanche photodiode manufactured according to the above method can yield an InP-based integrated near-infrared IGaAs single-photon avalanche detector chip, which can be applied to multiple fields such as future near-infrared quantum communication systems, free-space communication, laser ranging, spectral analysis, and environmental monitoring.

[0085] Those skilled in the art will understand that the features described in the various embodiments of this application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this application. In particular, the features described in the various embodiments of this application can be combined and / or combined in various ways without departing from the spirit and teachings of this application. All such combinations and / or combinations fall within the scope of this application.

[0086] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Without departing from the scope of this application, those skilled in the art can make various substitutions and modifications, all of which should fall within the scope of this application.

Claims

1. A single-photon avalanche photodiode, characterized in that, include: Substrate; The waveguide region on the substrate includes a first portion extending along a first direction and a second portion extending along a second direction, the first direction intersecting the second direction; The active region on the waveguide region extends along the first portion of the waveguide region; The depletion region on the active region; The contact layer on the depletion region; and The first electrode on the contact layer and the second electrode on the waveguide region; The single-photon avalanche photodiode is configured to transmit incident light along the first direction through the waveguide region to the active region to generate photogenerated carriers, and to transmit the photogenerated carriers to the depletion region.

2. The single-photon avalanche photodiode according to claim 1, characterized in that, The end of the depletion region is recessed relative to the end of the active region in the first direction.

3. The single-photon avalanche photodiode according to claim 1, characterized in that, The waveguide region includes a diluted waveguide region and an optical matching layer on the diluted waveguide region, wherein the end of the optical matching layer is recessed relative to the end of the diluted waveguide region in the first direction; The active region is on the optical matching layer, and the end of the active region is recessed relative to the end of the optical matching layer in the first direction.

4. The single-photon avalanche photodiode according to claim 1, characterized in that, The depletion region includes an etch barrier layer on the active region and an intrinsic layer on the etch barrier layer. In the first direction, the end of the contact layer is recessed relative to the end of the intrinsic layer, and in the first direction, the end of the intrinsic layer is recessed relative to the end of the etch barrier layer.

5. The single-photon avalanche photodiode according to any one of claims 1 to 4, characterized in that, The active region includes an absorption layer, a gradient layer, a charge layer, and a multiplication layer stacked sequentially on the waveguide region, wherein the thickness of the absorption layer in the vertical direction is 400 nm to 1 μm.

6. A method for manufacturing a single-photon avalanche photodiode, characterized in that, include: An epitaxial layer is formed on a substrate, the epitaxial layer comprising an epitaxial waveguide layer on the substrate, an epitaxial active layer on the epitaxial waveguide layer, an epitaxial depletion layer on the epitaxial active layer, and an epitaxial contact layer on the epitaxial depletion layer; Etch the epitaxial contact layer and the epitaxial depletion layer to expose the epitaxial active layer to form the contact layer and the depletion region; The epitaxial active layer is etched to expose the epitaxial waveguide layer to form an active region; The epitaxial waveguide layer is etched to expose the substrate to form a waveguide region, the waveguide region including a first portion extending along a first direction and a second portion extending along a second direction, the first direction intersecting the second direction; A first electrode is formed on the contact layer and a second electrode is formed on the waveguide region; The single-photon avalanche photodiode is configured to transmit incident light along the first direction through the waveguide region to the active region to generate photogenerated carriers, and to transmit the photogenerated carriers to the depletion region.

7. The method according to claim 6, characterized in that, The etching of the epitaxial active layer to expose the epitaxial waveguide layer to form an active region includes: A first mask is formed on the epitaxial active layer; Based on the pattern of the first mask, the epitaxial active layer is etched to form the active region, such that in a first direction, the end of the depletion region is recessed relative to the end of the active region.

8. The method according to claim 6, characterized in that, The etching of the epitaxial waveguide layer to expose the substrate to form a waveguide region includes: A second mask is formed on the epitaxial waveguide layer; Based on the pattern of the second mask, the epitaxial waveguide layer is etched to form the waveguide region, such that in the first direction, the end of the active region is recessed relative to the end of the waveguide region.

9. The method according to claim 8, characterized in that, The waveguide region includes a diluted waveguide region and an optical matching layer on the diluted waveguide region, and the method further includes: A third mask is formed on the waveguide region; Based on the pattern of the third mask, a portion of the optical matching layer in the first direction is etched such that, in the first direction, the end of the retained optical matching layer is recessed relative to the end of the diluted waveguide region.

10. The method according to claim 6, characterized in that, The epitaxial depletion layer includes an etch barrier layer on the epitaxial active layer and an intrinsic layer on the etch barrier layer; The etching of the epitaxial contact layer and the epitaxial depletion layer to expose the epitaxial active layer to form the contact layer and the depletion region includes: The etching barrier layer, the intrinsic layer, and the epitaxial contact layer are etched in stages, such that in the first direction, the end of the etched contact layer is recessed relative to the end of the etched intrinsic layer, and the end of the etched intrinsic layer is recessed relative to the end of the etched etching barrier layer.

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