Avalanche photodiode structure for inhibiting avalanche composite light-emitting crosstalk
By setting a composite light-emitting anti-reflection layer and a backlight-side absorption layer in the pixel unit of an avalanche photodiode, and designing the film layer by utilizing the difference in light source position and wavelength, the problems of avalanche composite light emission crosstalk and signal leakage are solved, thereby improving the detection performance and communication security of the avalanche photodiode.
Patent Information
- Application Number
- CN202511541528.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-27
- Publication Date
- 2026-01-13
Smart Images
Figure CN121335233A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of photoelectric detection technology, and specifically relates to an avalanche photodiode structure for suppressing avalanche recombination crosstalk. Background Technology
[0002] An avalanche photodiode (APD) is a photodetector diode that uses the avalanche multiplication effect of charge carriers to amplify photoelectric signals to improve detection sensitivity. It is commonly used in depth detection (including lidar), medical sensing, machine vision, gesture recognition, quantum science and other fields.
[0003] A typical avalanche photodiode (APD) structure is based on a P / N junction, P / I / N junction, or P / I / P / I / N junction, with a substrate material and passivation layer superimposed. It is generally a mesa or planar device structure, and typically includes multiple pixel units. When a pixel unit captures an external photon and undergoes avalanche multiplication, a large number of hot carriers are generated. During the relaxation of these hot carriers, the recombination of hot electrons and hot holes leads to a small amount of broadband photon radiation, a phenomenon known as "avalanche recombination luminescence." Existing typical avalanche photodiodes, such as Si APDs, SiC APDs, and GaN APDs, all exhibit the "avalanche recombination luminescence" phenomenon. This phenomenon causes multiple levels of "avalanche recombination luminescence crosstalk" during APD applications, severely limiting their use in high-sensitivity detection fields. Specifically, this manifests in two ways: Firstly, the avalanche recombination luminescence spectral range partially overlaps with the incident light response spectral range. For example, the incident light response spectral range of SiAPDs is 300nm-1000nm, while the avalanche luminescence spectral range is 650nm-1100nm; GaN... The incident light response spectrum of an APD is approximately 250nm-410nm, while the spectrum of avalanche recombination emission is approximately 360nm-600nm. This overlap in spectral ranges can cause avalanche recombination emission photons from one pixel unit to propagate to neighboring pixels, potentially triggering avalanche breakdown in other pixels as well. This results in a signal not caused by actual incident photons, leading to increased crosstalk in the device and noise or artifacts in the image. On the other hand, photons generated by avalanche recombination emission may be emitted again through the incident surface, causing signal leakage. This also limits its application in highly sensitive fields. For example, in the field of quantum secure communication, emitted avalanche recombination emission radiation allows eavesdroppers to steal information from photons returning to the channel, threatening communication security.
[0004] Avalanche-induced co-emission crosstalk is a common phenomenon in existing APD applications. Some existing technologies can suppress the crosstalk between APD pixels caused by avalanche emission to a certain extent by setting up physical isolation structures between pixels. However, existing technologies cannot effectively suppress the signal leakage caused by emission within avalanche-emitting pixels. Summary of the Invention
[0005] The purpose of this invention is to propose an avalanche photodiode structure that suppresses avalanche recombination crosstalk, which can suppress both inter-pixel crosstalk caused by avalanche recombination and intra-pixel signal leakage caused by avalanche recombination.
[0006] This invention is achieved through the following technical solution:
[0007] This invention proposes an avalanche photodiode structure for suppressing avalanche recombination emission crosstalk, comprising multiple isolated pixel units. Each pixel unit includes a substrate layer, a structural layer, and a passivation layer. The pixel unit further includes a recombination emission antireflection layer, an incident light antireflection layer, and a recombination emission absorption layer. The recombination emission antireflection layer and the incident light antireflection layer are sequentially disposed on the light-incoming side of the passivation layer. The passivation layer and the recombination emission antireflection layer together form a reflective film for avalanche recombination emission. The passivation layer, the recombination emission antireflection layer, and the incident light antireflection layer together constitute an incident light antireflection film. The recombination emission absorption layer is either the substrate layer or a separate film layer disposed on one side of the substrate layer, used to absorb avalanche recombination emission photons reflected by the recombination emission antireflection layer.
[0008] Preferably, the composite light-emitting reflective layer is a dual-functional film layer formed by periodically stacking dielectric layers. It enhances reflection of avalanche composite light emission on one side of the structural layer and enhances transmission of external incident light on the other side. The single-layer thickness, dielectric material, and number of periods of the dielectric layer are comprehensively set according to the peak wavelength of the incident light and the peak wavelength of the avalanche composite light emission.
[0009] Preferably, the structural layer is the structural layer of a silicon avalanche photodiode; the passivation layer material is a single-period SiO2 film with a thickness of 5-200 nm; the incident light antireflection layer material is a single-period MgF2 film with a thickness of 100-150 nm; the substrate layer is used as a light absorption layer; the composite light-emitting and reflective layer is formed by periodically combining TiO2 and SiO2 as media, with a composite period of 4-8 periods, wherein the thickness of the TiO2 media layer is 50-100 nm and the thickness of the SiO2 media layer is 120-180 nm.
[0010] Furthermore, the passivation layer, the incident light antireflection layer, and the composite light emission antireflection layer are all designed with a 650nm incident light peak wavelength and an 850nm avalanche composite light emission peak wavelength.
[0011] Furthermore, the refractive index of the passivation layer for incident light is set to 1.48-1.44, and the refractive index for avalanche recombination luminescence is set to 1.47-1.43; the refractive index of the antireflection layer for incident light is set to 1.40-1.46, and the refractive index for avalanche recombination luminescence is set to 1.39-1.45; the refractive index of the TiO2 dielectric layer in the antireflection layer for incident light is set to 2.52-2.48, and the refractive index for avalanche recombination luminescence is set to 2.42-2.38; the refractive index of the SiO2 dielectric layer in the antireflection layer for incident light is set to 1.47-1.45, and the refractive index for avalanche recombination luminescence is set to 1.46-1.44.
[0012] Preferably, the structural layer is the structural layer of a nitride avalanche photodiode; the composite light absorption layer is a microcrystalline silicon layer deposited on the backlight side of the substrate, with a deposition thickness of 1000-2000 nm; the passivation layer is a single-period SiO2 film with a thickness of 0-100 nm; the antireflection layer is formed by periodically combining HfO2 and SiO2 as dielectrics, with a composite period of 4-8 periods, wherein the thickness of the HfO2 dielectric layer is 40-60 nm and the thickness of the SiO2 dielectric layer is 50-80 nm; and the incident antireflection layer is a single-period MgF2 structure with a thickness of 50-80 nm.
[0013] Furthermore, the passivation layer, the incident light antireflection layer, and the composite light emission antireflection layer are all designed with an incident light peak wavelength of 340nm and an avalanche composite light emission peak wavelength of 410nm.
[0014] Furthermore, the refractive index of the passivation layer for incident light is set to 1.48-1.46, and the refractive index for avalanche co-luminescence is set to 1.47-1.45; the refractive index of the incident light antireflection layer for incident light is set to 1.40-1.36, and the refractive index for avalanche co-luminescence is set to 1.39-1.35; the refractive index of the HfO2 dielectric layer in the co-luminescence antireflection layer for incident light is set to 2.07-2.03, and the refractive index for avalanche co-luminescence is set to 2.02-1.98; the refractive index of the SiO2 dielectric layer in the co-luminescence antireflection layer for incident light is set to 1.48-1.46, and the refractive index for avalanche co-luminescence is set to 1.47-1.45.
[0015] The inventive concept of this invention lies in the fact that all avalanche photodiode structures possess the following characteristics: First, there is a significant difference between the peak wavelength of the response of existing avalanche photodiodes to external incident light and the peak wavelength of light emitted by the recombination of hot carriers in the APD; second, the incident light is incident from the outside of the device to the inside, while the avalanche recombination light is incident from the inside to the outside, resulting in differences in the light source position and propagation direction. This invention creatively utilizes these differences to optimize existing avalanche photodiodes by setting a dual-functional film layer on the light-incoming side of each pixel unit of the avalanche photodiode, which combines anti-reflection and anti-transmission functions. This allows the same film layer to both reflect the avalanche recombination light generated inside the device, blocking its emission or lateral dispersion, and to combine with the incident light anti-transmission layer on the light-incoming side to enhance the incident light transmittance and strengthen the external photon capture sensitivity. Simultaneously, a recombination light absorption layer is set on the substrate side (i.e., the backlight side) to absorb the recombination light photons reflected back by the recombination light anti-reflection layer, achieving self-digestion of recombination light within the APD within the avalanche pixel unit, greatly reducing crosstalk between intra-pixel recombination light and adjacent pixels.
[0016] Therefore, the avalanche photodiode structure for suppressing avalanche recombination crosstalk of the present invention has the following advantages or beneficial effects:
[0017] (1) This invention effectively overcomes the avalanche recombination crosstalk problem of existing avalanche photodiode structures. By setting a recombination reflection layer on the light-incoming side of the pixel unit and a recombination absorption layer on the back-light side, the avalanche recombination photons are digested inside the pixel unit as soon as they are generated, effectively blocking the avalanche recombination photons from lateral radiation to adjacent pixels, avoiding avalanche crosstalk caused by secondary avalanches triggered by neighboring pixels, and solving the imaging noise problem of avalanche photodiodes in photonic imaging fields such as medical imaging and lidar.
[0018] (2) This invention effectively overcomes the signal leakage problem of existing avalanche photodiode structures. By setting a composite light-emitting and reflective layer on the light-incoming side of the pixel unit and a composite light-emitting and absorption layer on the back-light side, it solves the problem of avalanche composite photons escaping from the light-incoming surface of the pixel, avoiding signal leakage and damage to the darkroom environment caused by the avalanche photodiode becoming a secondary light source. Therefore, this invention solves the application difficulties of avalanche photodiodes in highly sensitive detection fields such as quantum communication and bioluminescence.
[0019] (3) This invention overcomes the negative impact of setting a composite light emission enhancement layer on the transmittance of external incident light on the light-receiving surface. By utilizing the difference in peak wavelength of incident light and composite light emission and the difference in the position of the light source, a dual-function composite light emission enhancement layer is designed. It enhances the reflection of avalanche composite light emission on one side of the structural layer and enhances the transmission of external incident light on the other side. This allows the optimized avalanche photodiode to maintain the external quantum efficiency benchmark level and ensures the good detection performance of the avalanche photodiode. Attached Figure Description
[0020] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:
[0021] Figure 1 This is a schematic diagram illustrating the structure and working mechanism within a pixel unit of the present invention;
[0022] Figure 2 This is a schematic diagram of the structure of Embodiment 1 of the present invention;
[0023] Figure 3 This is a schematic diagram of the structure of Embodiment 2 of the present invention;
[0024] In the figure: 1. Composite light-emitting absorption layer; 2. Substrate layer; 3. Structural layer; 4. Passivation layer; 5. Composite light-emitting anti-reflection layer; 6. Incident light anti-reflection layer. Detailed Implementation
[0025] like Figure 1 As shown, this invention provides an avalanche photodiode structure for suppressing avalanche recombination crosstalk, comprising multiple isolated pixel units (each pixel unit is isolated using physical structures such as deep trenches, which are common in the art and therefore not specifically described in this invention and the accompanying drawings). Each pixel unit includes a substrate layer 2, a structural layer 3, a passivation layer 4, a recombination reflective layer 5, an incident light antireflection layer 6, and a recombination absorption layer 1. The recombination reflective layer 5 and the incident light antireflection layer 6 are sequentially disposed on the light-incoming side of the passivation layer 4. The recombination reflective layer 5 and the passivation layer 4 together form a reflective film for avalanche recombination, and together they constitute an incident light antireflection film. The recombination absorption layer 1 is either the substrate layer 2 or a separate film layer disposed on one side of the substrate layer 2, used to absorb the avalanche recombination photons reflected by the recombination reflective layer 5.
[0026] The specific structure of the composite light-emitting and reflective layer 5 is set by comprehensively considering the selected peak wavelength of incident light and the peak wavelength of avalanche composite light emission, so that the same film layer can simultaneously have the functions of enhancing avalanche composite light emission and enhancing the transmission of incident light.
[0027] As a preferred embodiment, the specific structural design method of the composite light-emitting anti-reflection layer 5 of the present invention is as follows: select a specific dielectric material according to the peak wavelength of the incident light and the peak wavelength of the avalanche composite light emission; determine the single-layer thickness and the number of periods of the dielectric layer according to the difference in the position of the light source and the optical path characteristics; periodically deposit different dielectric layers on the light-incoming side surface of the passivation layer 4 to form a composite film layer, which is the composite light-emitting anti-reflection layer 5.
[0028] The present invention will be further described in detail below using different types of avalanche photodiode structures as examples, but the implementation of the present invention is not limited thereto.
[0029] Example 1
[0030] This embodiment further elaborates on the existing planar device structure of silicon avalanche photodiodes, and provides a silicon avalanche photodiode structure (hereinafter referred to as Si APD) that suppresses avalanche recombination light emission crosstalk.
[0031] In this embodiment, a passivation layer 4, an incident light antireflection layer 6, and a composite light emission antireflection layer 5 are designed with a peak incident light wavelength of 650 nm and a peak avalanche recombination emission wavelength of 850 nm. After the Si APD completes the fabrication of the planar device structure (i.e., the basic structure consisting of substrate layer 2, structural layer 3, and passivation layer 4), the incident light antireflection layer 6 and the composite light emission antireflection layer 5 are deposited on the light-incoming side, and the composite light emission absorption layer 1 is deposited on the backlight side, thereby obtaining a silicon avalanche photodiode structure that suppresses avalanche recombination emission crosstalk.
[0032] Specifically, such as Figure 2 As shown, from one side of substrate 2 upwards, it includes:
[0033] (1) Substrate layer 2, the film material is N-type heavily doped silicon substrate. In this embodiment, the high absorption coefficient of the heavily doped silicon substrate for avalanche recombination emission at a preset peak wavelength is utilized. Substrate layer 2 also serves as recombination emission absorption layer 1 to simplify the preparation process.
[0034] (2) Si APD structure layer 3, which includes a P-type doped layer and an N-type doped layer to achieve avalanche breakdown of the PN junction.
[0035] (3) Passivation layer 4, the film material is SiO2, the thickness is set to 5-200nm, forming a single dielectric, single-period film with a refractive index range of 1.48-1.44 for 650nm incident light and a refractive index range of 1.47-1.43 for 850nm radiation recombination emission.
[0036] (4) Composite light-emitting and reflective layer 5, the film structure is a TiO2 / SiO2 periodic composite film, the number of composite periods is 4-8. Among them, the refractive index of the TiO2 film for 650nm incident light is 2.52-2.48, the refractive index for 850nm radiation light is 2.42-2.38, and the thickness of a single film layer is 50nm-100nm; the refractive index of the SiO2 film for 650nm incident light is 1.47-1.45, the refractive index for 850nm radiation composite light emission is 1.46-1.44, and the thickness of a single film layer is 120nm-180nm.
[0037] (5) Incident light antireflection layer 6 is a MgF2 single-period film with a thickness of 100nm-150nm; the refractive index range for 650nm incident light is 1.40-1.46, and the refractive index range for 850nm radiation recombination emission is 1.39-1.45.
[0038] The SiAPD for suppressing avalanche luminescence crosstalk in this embodiment forms a composite film consisting of a passivation layer 4, a composite luminescence antireflection layer 5, and an incident light antireflection layer 6 on the basis of the original planar device. The reflectivity of the active region avalanche luminescence with a peak wavelength of 850nm is >99%, and the reflection bandwidth (R>90%) is 810-890nm; the transmittance of incident light with a peak wavelength of 650nm is >99%, and the transmission bandwidth (T>90%) is 585-715nm. Combined with the substrate layer 2 as a composite luminescence absorption layer, it simultaneously achieves effective suppression of avalanche luminescence crosstalk and antireflection of incident visible light, achieving the intended invention effect.
[0039] Example 2
[0040] This embodiment further elaborates on the existing mesa device structure of gallium nitride avalanche photodiodes, and provides a gallium nitride avalanche photodiode structure (hereinafter referred to as GaN APD) that suppresses avalanche recombination light emission crosstalk.
[0041] In this embodiment, a passivation layer 4, an incident light antireflection layer 6, and a composite light emission antireflection layer 5 are designed with a peak incident light wavelength of 340 nm and a peak avalanche recombination emission wavelength of 410 nm. After the GaN APD completes the fabrication of the planar device structure (i.e., the basic structure consisting of substrate layer 2, structural layer 3, and passivation layer 4), the incident light antireflection layer 6 and the composite light emission antireflection layer 5 are deposited on the light-incoming side, and the composite light emission absorption layer 1 is deposited on the backlight side, thereby obtaining a gallium nitride avalanche photodiode structure that suppresses avalanche recombination emission crosstalk.
[0042] Specifically, such as Figure 3 As shown, from one side of substrate 2 upwards, it includes:
[0043] (1) Composite light-absorbing layer 1, the film material is microcrystalline silicon, and the thickness ranges from 1000 to 2000 nm. The film can be deposited on the back side of the substrate layer 2 by magnetron sputtering deposition equipment or other commonly used film deposition equipment.
[0044] (2) Substrate layer 2 is prepared using conventional substrate materials, such as sapphire substrate.
[0045] (3) GaN APD structure layer 3, which includes a P-type doped layer and an N-type doped layer to achieve avalanche breakdown of the PN junction.
[0046] (4) Passivation layer 4, the film material is SiO2, the thickness is set to 0-100nm, forming a single dielectric, single-period film with a refractive index range of 1.48-1.46 for 340nm incident light and a refractive index range of 1.47-1.45 for 410nm radiation recombination emission.
[0047] (5) Composite light-emitting and reflective layer 5, the film structure is a SiO2 / HfO2 periodic composite film, the number of composite periods is 4-8, wherein the refractive index of the HfO2 film for 340nm incident light is in the range of 2.07-2.03, the refractive index for 410nm radiation light is in the range of 2.02-1.98, and the single layer thickness is in the range of 40nm-60nm. The refractive index of the SiO2 film for 340nm incident light is in the range of 1.48-1.46, the refractive index for 410nm radiation composite light emission is in the range of 1.47-1.45, and the single layer thickness is in the range of 50nm-80nm.
[0048] (6) Incident light antireflection layer 6 is a MgF2 single-period film with a thickness of 100nm-150nm; the refractive index ranges from 1.40 to 1.36 for 340nm incident light and from 1.39 to 1.35 for 410nm radiation light.
[0049] The GaN APD for suppressing avalanche luminescence crosstalk in this embodiment forms a composite film consisting of a passivation layer 4, a composite luminescence antireflection layer 5, and an incident light antireflection layer 6 on the basis of the original planar device. The reflectivity of the active region avalanche luminescence with a peak wavelength of 410nm is >99%, and the reflection bandwidth (R>90%) is 380-450nm; the transmittance of incident light with a peak wavelength of 340nm is >99%, and the transmission bandwidth (T>90%) is 320-365nm. Combined with the composite luminescence absorption layer 1, it simultaneously achieves effective suppression of avalanche luminescence crosstalk and antireflection of incident ultraviolet light, achieving the intended invention effect.
[0050] The embodiments described above are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The scope of the present invention is not limited to the specific embodiments described above. All equivalent changes or modifications made in accordance with the spirit disclosed in the present invention are still covered within the protection scope of the present invention.
Claims
1. An avalanche photodiode structure for suppressing avalanche recombination crosstalk, comprising multiple mutually isolated pixel units, each pixel unit comprising a substrate layer (2), a structural layer (3), and a passivation layer (4), characterized in that: The pixel unit further includes a composite light-emitting reflective layer (5), an incident light anti-reflection layer (6), and a composite light-emitting absorption layer (1). The composite light-emitting reflective layer (5) and the incident light anti-reflection layer (6) are sequentially disposed on the light-incoming side of the passivation layer (4). The passivation layer (4) and the composite light-emitting reflective layer (5) together form an avalanche composite light-emitting reflective film. The passivation layer (4), the composite light-emitting reflective layer (5), and the incident light anti-reflection layer (6) together constitute an incident light anti-reflection film. The composite light-emitting absorption layer (1) is the substrate layer (2) or a separate film layer disposed on one side of the substrate layer (2), used to absorb the avalanche composite light-emitting photons reflected by the composite light-emitting reflective layer (5).
2. The avalanche photodiode structure for suppressing avalanche recombination crosstalk according to claim 1, characterized in that: The composite light-emitting and reflective layer (5) is a dual-function film layer formed by periodically stacking dielectric layers. It enhances the reflection of avalanche composite light emission on one side of the structural layer (3) and enhances the transmission of external incident light on the other side. The thickness of each layer, dielectric material and number of periods of the dielectric layer are comprehensively set according to the peak wavelength of the incident light and the peak wavelength of the avalanche composite light emission.
3. The avalanche photodiode structure for suppressing avalanche recombination crosstalk according to claim 1, characterized in that: The structural layer (3) is the structural layer (3) of a silicon avalanche photodiode. The passivation layer (4) is made of SiO2 single-period film with a thickness of 5-200 nm. The incident light anti-reflection layer (6) is made of MgF2 single-period film with a thickness of 100-150 nm. The substrate layer (2) is used as a light absorption layer. The composite light-emitting anti-reflection layer (5) is formed by periodically combining TiO2 and SiO2 as media, with a composite period of 4-8 periods. The thickness of the TiO2 media layer is 50-100 nm, and the thickness of the SiO2 media layer is 120-180 nm.
4. The avalanche photodiode structure for suppressing avalanche recombination crosstalk according to claim 3, characterized in that: The passivation layer (4), the incident light anti-reflection layer (6), and the composite light emission anti-reflection layer (5) are all designed with a peak incident light wavelength of 650 nm and a peak avalanche composite light emission wavelength of 850 nm.
5. The avalanche photodiode structure for suppressing avalanche recombination crosstalk according to claim 4, characterized in that: The passivation layer (4) has a refractive index range of 1.48-1.44 for incident light and a refractive index range of 1.47-1.43 for avalanche recombination luminescence; the antireflection layer has a refractive index range of 1.40-1.46 for incident light and a refractive index range of 1.39-1.45 for avalanche recombination luminescence; the TiO2 dielectric layer in the antireflection layer has a refractive index range of 2.52-2.48 for incident light and a refractive index range of 2.42-2.38 for avalanche recombination luminescence; the SiO2 dielectric layer in the antireflection layer has a refractive index range of 1.47-1.45 for incident light and a refractive index range of 1.46-1.44 for avalanche recombination luminescence.
6. The avalanche photodiode structure for suppressing avalanche recombination crosstalk according to claim 1, characterized in that: The structural layer (3) is the structural layer (3) of the nitride avalanche photodiode. The composite light absorption layer is a microcrystalline silicon layer deposited on the backlight side of the substrate layer (2), and the thickness of the microcrystalline silicon layer is 1000-2000nm. The passivation layer (4) is a single-period SiO2 film with a thickness of 0-100nm. The antireflection layer is formed by periodically combining HfO2 and SiO2 as media, with a composite period of 4-8 periods. The thickness of the HfO2 media layer is 40-60nm, and the thickness of the SiO2 media layer is 50-80nm. The incident antireflection layer is a single-period MgF2 structure with a thickness of 50-80nm.
7. The avalanche photodiode structure for suppressing avalanche recombination crosstalk according to claim 6, characterized in that: The passivation layer (4), the incident light anti-reflection layer (6), and the composite light emission anti-reflection layer (5) are all designed with an incident light peak wavelength of 340 nm and an avalanche composite light emission peak wavelength of 410 nm.
8. The avalanche photodiode structure for suppressing avalanche recombination crosstalk according to claim 7, characterized in that: The passivation layer (4) has a refractive index range of 1.48-1.46 for incident light and a refractive index range of 1.47-1.45 for avalanche co-luminescence. The incident light antireflection layer (6) has a refractive index range of 1.40-1.36 for incident light and a refractive index range of 1.39-1.35 for avalanche co-luminescence. The HfO2 dielectric layer in the co-luminescence antireflection layer (5) has a refractive index range of 2.07-2.03 for incident light and a refractive index range of 2.02-1.98 for avalanche co-luminescence. The SiO2 dielectric layer in the co-luminescence antireflection layer (5) has a refractive index range of 1.48-1.46 for incident light and a refractive index range of 1.47-1.45 for avalanche co-luminescence.