Asymmetric optical resonance avalanche photodiode and photosensitive array
By designing an asymmetric optical resonant structure, the problems of dark current and power consumption caused by the increased thickness of the absorption layer in avalanche photodiodes are solved, achieving efficient photon absorption and low dark current, which is suitable for weak light signal detection and high-speed optical communication.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-15
- Publication Date
- 2026-03-13
AI Technical Summary
The increased absorption layer thickness of existing avalanche photodiodes leads to high dark current and high power consumption, and poor consistency of the applied operating voltage of the pixels in the array, which affects the device performance.
An asymmetric optical resonance structure is adopted, including a top reflector and a bottom high-reflectivity metal film, to form an asymmetric optical resonance structure. Combined with a gradient refractive layer and a DBR layer, the light transmittance and reflectance are improved, and the optical resonance effect is enhanced.
It improves the photon absorption efficiency of photodiodes, reduces dark current, maintains high signal-to-noise ratio and consistent operating voltage, and is suitable for weak light signal detection and high-speed optical communication.
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Figure CN121665701A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of photoelectric detection technology, and in particular to an asymmetric optical resonant avalanche photodiode and its photosensitive array. Background Technology
[0002] An avalanche photodiode (APD) is a highly sensitive photodetector that enables efficient detection of weak light signals through its internal avalanche multiplication effect. The principle involves utilizing the internal photoelectric effect of the absorption layer material to absorb incident photons, generating electron-hole pairs, which are then transported to a high-field multiplication layer for avalanche multiplication, thus producing a measurable large current. APD detectors are characterized by high sensitivity and fast response, and are commonly used in active laser detection to achieve three-dimensional imaging of targets. They have wide applications in quantum communication, 3D lidar, and other fields.
[0003] Currently, a common approach to improving the quantum efficiency of avalanche photodiodes is to increase the thickness of the absorption layer to enhance the absorption of incident light. However, this method has significant drawbacks: increasing the thickness of the absorption layer leads to increased dark current, thereby reducing the signal-to-noise ratio of the device; at the same time, a thicker absorption layer requires a higher breakdown voltage, which not only increases the power consumption of the device but also reduces the uniformity of the applied operating voltage among the pixels in the array. Summary of the Invention
[0004] This invention provides an asymmetric optical resonant avalanche photodiode and photosensitive array to solve the technical problems of traditional avalanche diodes having a thick absorption layer, resulting in large dark current and high power consumption.
[0005] This invention provides an asymmetric optical resonant avalanche photodiode, comprising: An electrode layer, within which a first window area is provided; A top reflector is disposed within the first window area. The transmittance of the incident side of the top reflector to light with the target wavelength is higher than a preset transmittance threshold, and the reflectance of the exit side to light with the target wavelength is higher than a preset reflectance threshold. A substrate is disposed on the emission side of the top reflector; A buffer layer is disposed on the side of the substrate opposite to the top reflector; An active region is located on the side of the buffer layer opposite to the top reflector; A bottom high-reflectivity metal film is disposed on both sides of the active region opposite to the top reflector. The reflectivity of the bottom high-reflectivity metal film closer to the active region is higher than the reflectivity threshold for the tube of the target wavelength. The top reflector and the bottom high-reflectivity metal film form an asymmetric optical resonant structure.
[0006] In one embodiment of the present invention, the top reflector comprises: an anti-reflection layer, a gradient refractive layer and a DBR layer stacked sequentially, wherein the anti-reflection layer is located on the incident side of the top reflector to receive incident light; the gradient refractive layer is composed of multiple discrete dielectric films with different refractive indices, and the refractive index of each discrete dielectric film increases sequentially from the incident side to the exit side.
[0007] In one embodiment of the present invention, the antireflective layer is composed of a single-layer dielectric film, and the refractive index n0 of the single-layer dielectric film is:
[0008] Wherein, n1 is the refractive index of the discrete dielectric film closest to the antireflection layer in the gradient refractive layer; The thickness of the anti-reflective layer for:
[0009] in, The target wavelength.
[0010] In one embodiment of the present invention, the material of the anti-reflective layer is one of MF2, Al2O3, and ZnS.
[0011] In one embodiment of the present invention, the DBR layer is obtained by periodically alternating two dielectric thin films with different refractive indices, such that the reflectivity of the DBR layer is greater than 90%.
[0012] In one embodiment of the present invention, the total thickness of the gradient refractive layer is greater than half of the target wavelength, and the incident light transmittance of the gradient refractive layer is greater than 90%.
[0013] In one embodiment of the present invention, the active region is composed of an absorption layer, a multiplication layer, a gradient layer and a charge layer stacked sequentially. The absorption layer is close to the top reflector, and the charge layer is close to the bottom high-reflectivity metal film. The material of the absorption layer includes one of InGaAs, InGaAsP, mercury cadmium telluride, AlGaN, Si or Ge.
[0014] In one embodiment of the present invention, the avalanche photodiode further includes a first passivation layer, a second window region is disposed within the first passivation layer, and the second window region is disposed opposite to the first window region, wherein the bottom high-reflectivity metal film is disposed within the second window region.
[0015] In one embodiment of the present invention, a second passivation layer is further disposed on the side of the stacked structure formed by the electrode, the top reflector, the substrate, the buffer layer, the active region and the bottom high-reflectivity metal film, and the second passivation layer and the first passivation layer serve as protective layers for the stacked structure.
[0016] The present invention also provides a photosensitive array comprising a plurality of the aforementioned asymmetric optical resonant avalanche photodiodes, wherein the avalanche photodiodes are arranged in an array.
[0017] The beneficial effects of this invention are as follows: This invention proposes an asymmetric optical resonant avalanche photodiode and photosensitive array. Through an asymmetric top reflector, the light exhibits high transmittance for the target wavelength on the incident side and high reflectivity on the emitting side. This, combined with the bottom high-reflectivity metal film, forms an optical resonant structure, achieving filtering and enhanced absorption. The bottom high-reflectivity metal film has low manufacturing difficulty and is suitable for fabricating large-array devices. Attached Figure Description
[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.
[0019] In the attached diagram: Figure 1 This is a schematic cross-sectional view of an asymmetric optical resonant avalanche photodiode in one embodiment of the present invention. Figure 2 This is a schematic cross-sectional view of the photosensitive array in one embodiment of the present invention.
[0020] The attached figures are labeled as follows: 1-Top reflector; 2-Electrode layer; 3-Substrate; 4-Buffer layer; 5-Active region; 6-First passivation layer; 7-Bottom high-reflectivity metal film; 8-Second passivation layer. Detailed Implementation
[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.
[0022] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.
[0023] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.
[0024] Avalanche photodiodes (APDs) and their arrays typically employ a single-absorption-layer structure. After photons enter the absorption layer, some are absorbed and converted into photogenerated carriers, while others penetrate the material. Therefore, the thicker the absorption layer, the higher the quantum efficiency. However, since the magnitude of the dark current caused by recombination in the device's dark current component is directly proportional to the absorption layer thickness, this method of achieving high quantum efficiency by increasing the absorption layer thickness will additionally increase the dark current and reduce the signal-to-noise ratio. Specifically, for APD arrays, the following drawbacks exist: first, a thick absorption layer implies a large breakdown voltage, which reduces the consistency of the applied operating voltage across the array pixels; second, a thick absorption layer increases the carrier transport length, thereby increasing timing jitter and degrading device performance. The challenge in device structure design is to improve quantum efficiency without increasing the absorption layer thickness. Currently, a commonly used technique is to employ a symmetrical DBR optical resonator design, where both the top and bottom mirrors are high-reflectivity DBRs. Furthermore, the higher the DBR reflectivity, the better the resonance-enhanced absorption effect.
[0025] However, in actual device design, due to the transmittance requirements of the incident light flux, the reflectivity of the top reflector 1 is generally between 40% and 50%. This symmetrical optical structure often weakens the enhanced absorption effect of the resonant cavity.
[0026] Meanwhile, the performance of DBR is related to the number of stacked material layers. In order to achieve the ideal high reflectivity, DBR often has dozens of layers, which makes the process complex, and the response wavelength of this structure is affected by temperature.
[0027] Based on the problems existing in the above-mentioned related technologies, this application provides an asymmetric optical resonant avalanche photodiode and a photosensitive array. The technical solution of this application will be described in detail below with reference to specific embodiments.
[0028] Please see Figure 1 , Figure 1This is a cross-sectional schematic diagram of an asymmetric optical resonant avalanche photodiode according to an embodiment of the present invention. The asymmetric optical resonant avalanche photodiode includes an electrode layer 2, a top reflector 1, a substrate 3, a buffer layer 4, an active region 5, and a bottom high-reflectivity metal film 7. A first window region is provided within the electrode layer 2, and the top reflector 1 is disposed within the first window region. The transmittance of the incident side of the top reflector 1 for light of the target wavelength is higher than a preset transmittance threshold, and the reflectance of the emitting side for light of the target wavelength is higher than a preset reflectance threshold. The substrate 3 is disposed on the emitting side of the top reflector 1, and the buffer layer 4 is disposed on the side of the substrate 3 opposite to the top reflector 1. The active region 5 is disposed on the side of the buffer layer 4 opposite to the top reflector 1, and the bottom high-reflectivity metal film 7 is disposed opposite to the top reflector 1 on both sides of the active region 5. The buffer layer 4 is designed to adapt to the interface between the substrate 3 and the active region 5, reducing lattice mismatch. The bottom highly reflective metal film 7, near the active region 5, has a reflectivity higher than the reflectivity threshold for light with the target wavelength, and the top reflector 1 and the bottom highly reflective metal film 7 form an asymmetric optical resonance structure. Both the transmittance and reflectivity thresholds can be set to 90%. Of course, they can also be adjusted according to actual detection needs; no restrictions are imposed here.
[0029] In one embodiment, the top reflector 1 comprises an antireflective layer, a graded refractive index layer, and a DBR layer stacked sequentially. The antireflective layer is located on the incident side of the top reflector 1 and is used to receive incident light. The graded refractive index layer is composed of multiple discrete dielectric films with different refractive indices, and the refractive index of each discrete dielectric film increases sequentially from the incident side to the exit side. This graded refractive index structure can effectively reduce the reflection loss of incident light at the interface and improve the light transmittance.
[0030] The antireflective layer consists of a single-layer dielectric film, and the refractive index n0 of the single-layer dielectric film is:
[0031] Where n1 is the refractive index of the discrete dielectric film closest to the antireflective layer in the gradient refractive layer.
[0032] Thickness of anti-reflective layer for:
[0033] Where λ is the target wavelength.
[0034] In one embodiment, the antireflective layer is made of MgF2 with a refractive index of approximately 1.38, suitable for the visible to near-infrared wavelength range. In another embodiment, the antireflective layer is made of Al2O3 with a refractive index of approximately 1.76, suitable for the ultraviolet to visible wavelength range. In yet another embodiment, the antireflective layer can also be made of ZnS with a refractive index of approximately 2.3, suitable for the infrared wavelength range. Different antireflective layer materials can be selected based on different application scenarios and target wavelengths to achieve the best antireflective effect.
[0035] In one embodiment, the DBR layer is formed by periodically alternating two dielectric thin films with different refractive indices, resulting in a reflectivity greater than 90%. This periodic structure forms a distributed Bragg reflector capable of producing high reflectivity within a specific wavelength range, playing a crucial role in improving the quality factor of optical resonators. The high reflectivity of the DBR layer is closely related to the refractive index difference of the dielectric thin films and the number of periods; a higher number of periods results in higher reflectivity, but also increases manufacturing difficulty and cost. The specific number of dielectric thin film layers in the DBR layer can be designed and adjusted according to actual application requirements.
[0036] In one embodiment, the total thickness of the gradient refractive layer is greater than half the target wavelength, and the incident light transmittance of the gradient refractive layer is greater than 90%. This design ensures sufficient optical thickness to achieve a good gradient refractive effect while maintaining high transmittance and reducing light energy loss. As a transition layer between the antireflective layer and the DBR layer, the gradient refractive layer not only improves the overall optical performance but also enhances the structural stability between the layers.
[0037] In one embodiment, the active region 5 consists of an absorption layer, a multiplication layer, a gradient layer, and a charge layer stacked sequentially. The absorption layer is located near the top reflector 1, and the charge layer is located near the bottom high-reflectivity metal film 7. The material of the absorption layer can be selected from InGaAs, InGaAsP, mercury cadmium telluride, AlGaN, Si, or Ge, depending on the application scenario and target wavelength range. For example, InGaAs material has high absorption efficiency in the near-infrared band and is suitable for optical communication; while AlGaN material is suitable for ultraviolet detection.
[0038] In one embodiment, the absorption layer converts incident photons into electron-hole pairs, the multiplication layer amplifies the number of initially generated charge carriers through the avalanche effect, the gradient layer adjusts the band structure to optimize charge carrier transport, and the charge layer collects and outputs electrical signals. This multilayer structure design gives the avalanche photodiode high sensitivity and fast response characteristics.
[0039] In one embodiment, the asymmetric optical resonant avalanche photodiode further includes a first passivation layer 6, within which a second window region is disposed opposite to the first window region, and a bottom highly reflective metal film 7 is disposed within the second window region. The first passivation layer 6 can effectively protect the device structure, preventing external environmental corrosion, and simultaneously control the effective area of photoelectric conversion through precisely defined window regions. The first passivation layer 6 can employ a high-density dielectric film, which can reduce surface dark current and thus effectively protect the chip surface.
[0040] In one embodiment, a second passivation layer 8 is further disposed on the side of the stacked structure formed by the electrode layer 2, the top reflector 1, the substrate 3, the buffer layer 4, the active region 5, and the bottom high-reflectivity metal film 7. The second passivation layer 8 and the first passivation layer 6 serve as protective layers for the stacked structure. This dual passivation layer structure not only provides all-round protection but also helps to reduce the dark current of the device and improve the signal-to-noise ratio and detection sensitivity.
[0041] During operation, the incident light first passes through the antireflection layer to reduce surface reflection loss; then it passes through the graded refractive layer to further reduce interface reflection; finally, it passes through the DBR layer and enters the active region 5. In the active region 5, photons are absorbed by the absorption layer and converted into electron-hole pairs. These initial charge carriers are amplified in the multiplication layer through the avalanche effect, ultimately forming a detectable electrical signal output. Simultaneously, unabsorbed light is reflected back to the active region 5 by the bottom high-reflectivity metal film 7, increasing the photon absorption probability and improving quantum efficiency.
[0042] The asymmetric optical resonant structure formed by the top reflector 1 and the bottom highly reflective metal film 7 enhances the standing wave effect in the active region 5, significantly improving photon absorption efficiency. Besides forming the asymmetric optical resonant structure with the top reflector 1, the bottom highly reflective metal film also serves as an electrode. This asymmetric optical resonant structure design, combined with the internal amplification mechanism of the avalanche photodiode, enables the device to maintain high response speed while exhibiting higher photoelectric conversion efficiency and sensitivity, making it suitable for applications such as weak light signal detection, high-speed optical communication, and quantum information processing.
[0043] Please see Figure 2 , Figure 2 This is a cross-sectional structural diagram of a photosensitive array according to one embodiment of the present invention. The present invention also provides a photosensitive array comprising multiple asymmetric optically resonant avalanche photodiodes, wherein the avalanche photodiodes are arranged in an array.
[0044] Each avalanche photodiode has the same structure as the asymmetric optical resonant avalanche photodiode described in the preceding embodiments, including an electrode layer, a top reflector, a substrate, a buffer layer, an active region, and a bottom highly reflective metal film. A first window region is formed within the electrode layer, and the top reflector is disposed within the first window region. The transmittance of the incident side of the top reflector for light of the target wavelength is higher than a preset transmittance threshold, and the reflectance of the emitting side for light of the target wavelength is higher than a preset reflectance threshold. The substrate is disposed on the emitting side of the top reflector, and the buffer layer is disposed on the side of the substrate facing away from the top reflector. The active region is disposed on the side of the buffer layer facing away from the top reflector, and the bottom highly reflective metal film is disposed opposite to the top reflector on both sides of the active region. The reflectance of the bottom highly reflective metal film near the active region is higher than a preset reflectance threshold, and the top reflector and the bottom highly reflective metal film form an asymmetric optical resonant structure.
[0045] In this photosensitive array, multiple avalanche photodiodes are arranged in a matrix to form a two-dimensional array structure. Each avalanche photodiode, as a pixel unit in the array, can independently perform photoelectric conversion. This array arrangement enables the photosensitive array to capture two-dimensional image information, achieving spatially resolved photoelectric detection. The arrangement of the avalanche photodiodes in the photosensitive array can be set and adjusted according to actual application requirements, and is not limited here.
[0046] In one embodiment, the avalanche photodiodes in the array can be integrated on the same chip via a common underlying substrate, and each diode unit is connected to an external readout circuit via an independent electrode lead. The array structure can be designed with different sizes and densities according to application requirements, such as 8×8, 16×16, 32×32, or larger arrays.
[0047] Each avalanche photodiode unit in the photosensitive array can be designed with the same spectral response characteristics for detection in a single wavelength range; or it can be designed with different spectral response characteristics. By adjusting the structural parameters of the top reflector of different units, it can selectively respond to light of different wavelengths, thereby achieving multispectral or hyperspectral imaging functions.
[0048] This photosensitive array can be applied to low-light imaging, high-speed optical communication receiver arrays, 3D lidar, quantum communication receivers, and other fields. Due to the use of an asymmetric optical resonant structure, each avalanche photodiode unit in the array has high sensitivity and fast response characteristics, enabling the entire array to maintain good signal-to-noise ratio and imaging quality even under low-light conditions.
[0049] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. An asymmetric optical resonant avalanche photodiode, characterized in that, include: An electrode layer, within which a first window area is provided; A top reflector is disposed within the first window area. The transmittance of the incident side of the top reflector to light with the target wavelength is higher than a preset transmittance threshold, and the reflectance of the exit side to light with the target wavelength is higher than a preset reflectance threshold. A substrate is disposed on the emission side of the top reflector; A buffer layer is disposed on the side of the substrate opposite to the top reflector; An active region is located on the side of the buffer layer opposite to the top reflector; A bottom high-reflectivity metal film is disposed on both sides of the active region opposite to the top reflector. The reflectivity of the bottom high-reflectivity metal film closer to the active region is higher than the reflectivity threshold for the tube of the target wavelength. The top reflector and the bottom high-reflectivity metal film form an asymmetric optical resonant structure.
2. The asymmetric optical resonant avalanche photodiode according to claim 1, characterized in that, The top reflector comprises an anti-reflection layer, a gradient refractive layer, and a DBR layer stacked sequentially. The anti-reflection layer is located on the incident side of the top reflector to receive incident light. The gradient refractive layer is composed of multiple discrete dielectric films with different refractive indices, and the refractive index of each discrete dielectric film increases sequentially from the incident side to the exit side.
3. The asymmetric optical resonant avalanche photodiode according to claim 2, characterized in that, The antireflective layer is composed of a single-layer dielectric film, and the refractive index n0 of the single-layer dielectric film is: Wherein, n1 is the refractive index of the discrete dielectric film closest to the antireflection layer in the gradient refractive layer; The thickness of the anti-reflective layer for: in, The target wavelength is denoted as .
4. The asymmetric optical resonant avalanche photodiode according to claim 3, characterized in that, The anti-reflective layer is made of one of MF2, Al2O3, or ZnS.
5. The asymmetric optical resonant avalanche photodiode according to claim 2, characterized in that, The DBR layer is formed by periodically alternating two dielectric thin films with different refractive indices, resulting in a reflectivity of the DBR layer greater than 90%.
6. The asymmetric optical resonant avalanche photodiode according to claim 3, characterized in that, The total thickness of the gradient refractive layer is greater than half of the target wavelength, and the incident light transmittance of the gradient refractive layer is greater than 90%.
7. The asymmetric optical resonant avalanche photodiode according to claim 1, characterized in that, The active region consists of an absorption layer, a multiplication layer, a gradient layer, and a charge layer stacked sequentially. The absorption layer is close to the top reflector, and the charge layer is close to the bottom high-reflectivity metal film. The material of the absorption layer includes one of InGaAs, InGaAsP, mercury cadmium telluride, AlGaN, Si, or Ge.
8. The asymmetric optical resonant avalanche photodiode according to claim 1, characterized in that, It also includes a first passivation layer, in which a second window area is provided, and the second window area is disposed opposite to the first window area, and the bottom high-reflectivity metal film is disposed in the second window area.
9. The asymmetric optical resonant avalanche photodiode according to claim 8, characterized in that, A second passivation layer is further disposed on the side of the stacked structure formed by the electrode, the top reflector, the substrate, the buffer layer, the active region, and the bottom high-reflectivity metal film. The second passivation layer and the first passivation layer serve as protective layers for the stacked structure.
10. A photosensitive array, characterized in that, It includes a plurality of asymmetric optical resonant avalanche photodiodes as described in any one of claims 1-9, wherein each of the avalanche photodiodes is arranged in an array.