A GaN-based alpha particle detector and its preparation method

Abstract

The present application provides a GaN-based α-particle detector and a preparation method thereof, including a substrate and an epitaxial structure formed on the substrate by epitaxy, wherein the epitaxial structure includes a multi-quantum well layer. By introducing the multi-quantum well layer, the multi-quantum well layer absorbs the incident energy of the α-particle and correspondingly excites a large number of electron-hole pairs, and the electron-hole pairs are confined in the quantum wells by the quantum confinement effect of the multi-quantum well layer, which not only reduces the loss of electron-hole pair diffusion and recombination, but also prolongs the life of carriers, greatly improves the collection efficiency of the α-particle detector for carriers, ensures that more electron-hole pairs can be collected and converted into electrical signal output, thereby improving the performance of the α-particle detector.

Description

Technical Field

[0001] The present application relates to the technical field of alpha particle detection, and in particular to a GaN-based alpha particle detector and a preparation method thereof. Background Art

[0002] Alpha particles are radioactive particles that are widely used in nuclear radiation detection, nuclear safety monitoring, and environmental radiation detection. As the core component of the alpha particle detection system, the performance of the alpha particle detector directly affects the sensitivity, energy resolution, and reliability of the detection system. Traditional alpha particle detectors mainly use high-purity silicon materials, such as lithium drift silicon, ion implanted silicon, and gold silicon surface barrier detectors. Lithium drift silicon and ion implanted silicon detectors achieve energy collection and signal conversion of alpha particles through the PN junction of silicon, while gold silicon surface barrier detectors rely on Schottky surface barriers to accomplish the same function. However, with the increasing complexity of the application environment, especially under extreme conditions such as strong radiation and high temperature, silicon-based detectors have exposed a variety of problems, such as poor radiation resistance, poor high temperature performance, and insufficient signal stability.

[0003] In order to overcome the limitations of traditional alpha particle detectors, gallium nitride (GaN) materials have gradually become an ideal choice for the new generation of alpha particle detector materials due to their wide bandgap (3.4 eV), high breakdown electric field (3 MV / cm), excellent radiation resistance and good thermal stability. However, in the process of alpha particle detection, the existing single GaN structure has the problem that the energy of the incident alpha particles cannot be effectively converted into electron-hole pairs, and the GaN structure has insufficient charge binding ability, resulting in high charge recombination rate and low charge collection efficiency. Summary of the invention

[0004] The present application aims to solve one of the technical problems in the related art at least to some extent.

[0005] To this end, the first purpose of the present application is to propose a GaN-based α-particle detector and a preparation method thereof, which can further improve the detection sensitivity, energy resolution and response speed of the detector α-particles, and also have strong environmental adaptability and long-term reliability.

[0006] To achieve the above-mentioned purpose, the first embodiment of the present application proposes a GaN-based α-particle detector, comprising:

[0007] substrate;

[0008] An epitaxial structure is located on the substrate; the epitaxial structure includes a multi-quantum well layer, and the multi-quantum well layer is configured to provide a quantum confinement effect to confine carriers corresponding to the incident alpha particles in the multi-quantum well layer within the multi-quantum well layer.

[0009] Optionally, the multi-quantum well layer includes a multi-periodically stacked stacked structure, and the stacked structure includes any one of an AlGaN / GaN stack, an AlGaN / InGaN stack, an AlN / GaN stack or an InAlN / GaN stack.

[0010] Optionally, the number of stacking periods of the multi-periodic stacked layer structure is between 3 and 100 periods.

[0011] Optionally, the epitaxial structure further comprises a GaN buffer layer, an N-GaN layer, a barrier layer and a P-GaN layer stacked in sequence on the substrate, wherein the multi-quantum well layer is located between the barrier layer and the P-GaN layer.

[0012] Optionally, a stepped step is etched on a side of the epitaxial structure away from the substrate, and the stepped step includes an upper mesa and a lower mesa, the upper mesa is the upper surface of the P-GaN layer, and the lower mesa is the surface of the N-GaN layer exposed by etching.

[0013] Optionally, the detector further includes an electrode structure, the electrode structure includes a first electrode and a second electrode arranged at intervals, the first electrode is located on the upper surface, the second electrode is located on the lower surface, and the second electrode is arranged around the first electrode.

[0014] Optionally, the electrode structure is composed of a metal material with a high work function, and the electrode structure includes any one of Ni / Au, Pd / Au or Pt / Au metal combinations.

[0015] Optionally, the first electrode includes a first contact portion and a second contact portion, the first contact portion is a metal thin layer formed on the upper table surface, and the second contact portion is a metal column formed on the first contact portion.

[0016] Optionally, the thickness of the first contact portion ranges from 5 nm to 20 nm, and the thickness of the second contact portion ranges from 50 nm to 500 nm.

[0017] To achieve the above-mentioned purpose, the second embodiment of the present application proposes a method for preparing a GaN-based α-particle detector, comprising:

[0018] providing a substrate;

[0019] Forming an epitaxial stack layer on the substrate, wherein the epitaxial stack layer includes a GaN buffer layer, an N-GaN layer, a barrier layer, a multi-quantum well layer and a P-GaN layer stacked in sequence from bottom to top;

[0020] Etching is performed on the side of the epitaxial stack layer away from the substrate to form an epitaxial structure with a stepped step, wherein the stepped step includes an upper table and a lower table, wherein the upper table is the upper surface of the P-GaN layer, and the lower table is the surface of the N-GaN layer exposed by etching.

[0021] forming an electrode structure on the epitaxial structure, the electrode structure comprising a first electrode and a second electrode, the first electrode being located on the upper table surface, the second electrode being located on the lower table surface, and the second electrode surrounding a peripheral side of the first electrode;

[0022] A passivation layer is formed on the epitaxial structure, wherein the passivation layer covers the stepped steps and the side edges of the electrode structure and exposes the upper surfaces of the first electrode and the second electrode respectively.

[0023] The GaN-based α-particle detector and its preparation method provided in the present application have at least the following beneficial effects:

[0024] The GaN-based α-particle detector and its preparation method provided in the present application introduce a multi-quantum well layer into the epitaxial structure and utilize the special design of the multi-quantum well layer so that electrons and holes are confined in the quantum wells of the multi-quantum well layer. This quantum confinement effect not only reduces the loss of carrier (electrons and holes) diffusion and recombination, but also prolongs the lifetime of carriers, greatly improving the detector's efficiency in collecting carriers.

[0025] This application uses the difference between spontaneous polarization and piezoelectric polarization between multi-quantum well layers to form a built-in electric field in the multi-quantum well region. The direction of the built-in electric field is from N-GaN to P-GaN, running through the entire detection area. Under the action of the built-in electric field, electrons migrate rapidly along the conduction band to one end of the N-GaN layer, and holes migrate along the valence band to one end of the P-GaN layer. The built-in electric field enables carriers (electrons and holes) of different properties to automatically separate rapidly in different directions, effectively suppressing the recombination process and further improving the signal collection efficiency.

[0026] The present application can also adjust the energy response characteristics of the alpha particle detector to alpha particles by optimizing the thickness, composition and number of periods of the quantum well layer, thereby further enhancing the sensitivity and energy resolution of the alpha particle detector.

[0027] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0029] Figure 1 It is a schematic diagram of a top view structure of a GaN-based α-particle detector according to an embodiment of the present application.

[0030] Figure 2 Based on Figure 1 Schematic diagram of the cross-sectional structure of a GaN-based α-particle detector taken along line AA'.

[0031] Figure 3 Schematic diagram of the energy band of a GaN-based α-particle detector according to an embodiment of the present application.

[0032] Figure 4 It is a schematic flow chart of a method for preparing a GaN-based α-particle detector according to an embodiment of the present application.

[0033] 100 substrate; 210 GaN buffer layer; 220 N-GaN layer; 230 barrier layer; 240 multi-quantum well layer; 250 P-GaN layer; 310 first electrode; 311 first contact portion; 312 second contact portion; 320 second electrode; 400 passivation layer. DETAILED DESCRIPTION

[0034] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0035] GaN materials can work stably for a long time in high temperature and high radiation environments. At the same time, due to its wide bandgap characteristics, it can significantly reduce dark current and improve the sensitivity and signal-to-noise ratio of the detector, making GaN gradually become an ideal choice for the preparation of new generation alpha particle detectors. In addition, the high breakdown electric field and high saturation electron velocity characteristics of GaN-based devices give it significant advantages in the application of nuclear radiation detection.

[0036] However, α-particle detectors composed of a single GaN structure still face some problems in the process of α-particle detection. For example, the energy of the incident α-particles may not be fully or effectively converted into electron-hole pairs, or the traditional homogeneous GaN material has insufficient binding ability for electron and / or hole carriers, resulting in high charge recombination rate and low charge collection efficiency, which in turn affects the sensitivity and signal-to-noise ratio of α-particle detection.

[0037] Based on the above problems, the first aspect of the present application provides a GaN-based α-particle detector, such as Figure 1 and Figure 2As shown, the α-particle detector structure includes a substrate 100 and an epitaxial structure. The epitaxial structure is epitaxially formed on the substrate 100, and includes a GaN buffer layer 210, an N-GaN layer 220, a barrier layer 230, a multi-quantum well layer 240 and a P-GaN layer 250 stacked in sequence on the substrate 100.

[0038] It can be understood that the present application introduces a multi-quantum well layer 240 into the epitaxial structure of the alpha particle detector, so that when the alpha particle is incident on the detector, its incident energy will be absorbed by the multi-quantum well layer 240 and the material layer in the vicinity thereof, and a large number of electron-hole pairs will be excited in the multi-quantum well layer 240.

[0039] like Figure 3 As shown, due to the special design of the multi-quantum well layer 240 in the epitaxial structure, electrons and holes are confined in the quantum wells of the multi-quantum well layer 240. This quantum confinement effect not only reduces the loss of carrier (electrons and holes) diffusion and recombination, but also prolongs the carrier lifetime and greatly improves the carrier collection efficiency of the α-particle detector, ensuring that more electron-hole pairs can be collected and converted into electrical signal output, thereby improving the detection sensitivity of the α-particle detector.

[0040] The multi-quantum well layer 240 is formed by periodically alternating the growth of two materials with different bandgap widths, and the two materials with different bandgap widths include, but are not limited to, a stacked structure composed of any one of AlGaN / GaN, InGaN / GaN, AlN / GaN, etc. The stacked structure has strong spontaneous polarization characteristics and piezoelectric polarization characteristics, so that a strong built-in electric field is formed in the quantum well region of the multi-quantum well layer 240. The direction of the built-in electric field is from the N-GaN layer 220 to the P-GaN layer 250, and runs through the entire quantum well region. Under the action of the built-in electric field, electrons migrate rapidly along the conduction band to one end of the N-GaN layer 220, and holes migrate rapidly along the valence band to one end of the P-GaN layer 250. By quickly separating electron-hole pairs, the recombination process of electrons and holes is reduced, thereby improving the response speed of the alpha particle detector and further improving the collection efficiency of the alpha particle detection signal. After the electrons and holes are collected at one end of the N-GaN layer 220 (collecting electrons) and one end of the P-GaN layer 250 (collecting holes), respectively, corresponding electrical signals can be formed through an external circuit, and the strength of the electrical signals can directly reflect the energy of the incident α particles.

[0041] At the same time, due to the periodic structural characteristics of the multi-quantum well layer 240 and the selection of the stacked structure material, the multi-quantum well layer 240 can properly adjust the distribution and transfer path of carriers (electrons or holes), for example, by optimizing the thickness, composition and number of periods of the quantum well layer, thereby adjusting the response characteristics to the energy of alpha particles, reducing parasitic charge effects, reducing energy spectrum broadening, and further enhancing the sensitivity and energy resolution of the detector. Among them, the number of stacking periods of the stacked structure in the multi-quantum well layer 240 is between 3 and 100 periods.

[0042] The material of the substrate 100 includes but is not limited to any one of silicon, sapphire or silicon carbide, etc. The material of the barrier layer 230 includes but is not limited to any one of AlGaN, AlN or InAlN, etc.

[0043] As an example, the material of the substrate 100 is sapphire, which is an aluminum oxide crystal. As a substrate material, sapphire has high chemical stability, high thermal stability, excellent optical properties, good electrical properties, high mechanical properties and good biocompatibility.

[0044] The GaN buffer layer 210 formed on the sapphire is obtained by taking the sapphire c-plane as the substrate and growing along its crystal direction. The GaN buffer layer 210 helps to relieve the stress caused by the lattice mismatch between the materials, which helps to maintain the stability of the quantum well structure, thereby improving the epitaxial quality of the subsequent epitaxial formation of the N-GaN layer 220, the barrier layer 230, the multi-quantum well layer 240 and the P-GaN layer 250, and reducing the defect density.

[0045] In other examples, the material of the substrate 100 may also be a heavily doped high-resistance silicon substrate.

[0046] In some embodiments, a stair-like step is etched on one side of the epitaxial structure away from the substrate 100, and the stair-like step includes an upper mesa and a lower mesa with clear boundaries, the upper mesa is the upper surface of the P-GaN layer 250, and the lower mesa is the surface of the N-GaN layer 220 exposed by etching. The stair-like step can define the active area and realize the electrical isolation of the functional area of ​​the epitaxial structure.

[0047] In some embodiments, the alpha particle detector further includes an electrode structure and a passivation layer 400, wherein the electrode structure includes a first electrode 310 and a second electrode 320 which are arranged at intervals, wherein the first electrode 310 is located on the upper table surface, and the second electrode 320 is located on the lower table surface, and the second electrode 320 is arranged in a ring shape around the circumference of the first electrode 310. The first electrode 310 and the second electrode 320 are both composed of a metal material with a high work function, including but not limited to any one of Ni / Au, Pd / Au or Pt / Au metal combinations.

[0048] In addition, the first electrode 310 may specifically include a first contact portion 311 and a second contact portion 312, wherein the first contact portion 311 is a metal thin layer formed on the P-GaN layer 250, and the second contact portion 312 is a metal column formed on the first contact portion 311, so that the hole carriers collected and gathered on the P-GaN layer 250 can be connected to an external circuit through the first contact portion 311 and the second contact portion 312 in sequence.

[0049] The thickness design of the first contact portion 311 has a significant impact on the performance of the alpha particle detector, and an overly thick first contact portion 311 will cause significant energy loss when the alpha particles pass through the area, forming a detection dead zone, thereby reducing the charge collection efficiency and causing the energy spectrum to be broadened, thereby reducing the sensitivity and energy resolution of the alpha particle detector. Therefore, the present application designs the first electrode 310 as a first contact portion 311 in the form of a metal thin layer and a second contact portion 312 in the form of a metal column, and uses the first contact portion 311 with a thinner thickness and a larger area to cover the P-GaN layer 250, so as to significantly reduce the energy loss when the alpha particles are incident and pass through the first contact portion 311, and at the same time reduce the broadening of the alpha particle energy spectrum, thereby improving the sensitivity and energy resolution of the alpha particle detector.

[0050] At the same time, due to the limited thickness of the first contact portion 311, its mechanical strength is insufficient and it is difficult to directly withstand the pressure of gold wire bonding when the external circuit is electrically connected, thereby affecting the structural integrity of the α particle detector. Therefore, the present application also locally deposits a second contact portion 312 with a larger thickness and a smaller area on the first contact portion 311 to enhance the mechanical strength and bonding reliability of the corresponding area of ​​the first electrode 310, so that the external circuit can achieve stable gold wire bonding through the second contact portion 312, thereby enabling the first electrode 310 provided by the present application to meet the high performance and reliability advantages of the α particle detector, while also ensuring the structural integrity of the α particle detector.

[0051] As an example, the thickness of the first contact portion 311 ranges from 5 nm to 20 nm, the thickness of the second contact portion 312 ranges from 50 nm to 200 nm, and the area ratio between the second contact portion 312 and the first contact portion 311 on the P-GaN layer 250 should be less than 5%, and the second contact portion 312 with a smaller area can also reduce the energy loss of alpha particles when passing through the corresponding range of the second contact portion 312. In this example, the thickness of the first contact portion 311 is 20 nm, and the thickness of the second contact portion 312 is 100 nm.

[0052] The passivation layer 400 is formed on the epitaxial structure, so that the passivation layer 400 can cover the exposed surface of the upper mesa, the lower mesa, and the step surface between the upper mesa and the lower mesa of the epitaxial structure, so as to passivate the surface of the epitaxial structure, so that the inside of the epitaxial structure, especially the multi-quantum well layer, can be protected from the influence of the external environment, such as air, moisture, dust, etc., so as to ensure the stability of the performance of the multi-quantum well layer. At the same time, the passivation layer 400 also covers the side of the electrode structure, thereby exposing part of the upper surface of the first electrode 310 and the second electrode 320, so that the exposed surface of the first electrode 310 and the second electrode 320 can transmit the electrons collected by the N-GaN end and the holes collected by the P-GaN end to the external circuit to form an electrical signal reflecting the energy size of the alpha particles.

[0053] In summary, this embodiment provides a GaN-based α-particle detector, which combines the excellent physical properties of GaN materials with the quantum confinement effect, spontaneous polarization characteristics and piezoelectric polarization characteristics of the quantum well structure. It can not only significantly improve the detection sensitivity, energy resolution and response speed of α particles, but also has strong environmental adaptability and long-term reliability.

[0054] The second aspect of the present application provides a method for preparing a GaN-based α-particle detector, which is used to prepare the α-particle detector described in the above embodiment, such as Figure 1~Figure 4 As shown, the method may specifically include the following steps:

[0055] S1, providing a substrate 100;

[0056] S2, forming an epitaxial stack layer on the substrate 100, wherein the epitaxial stack layer includes a GaN buffer layer 210, an N-GaN layer 220, a barrier layer 230, a multi-quantum well layer 240 and a P-GaN layer 250 stacked in sequence from bottom to top;

[0057] S3, etching is performed on the side of the epitaxial stack layer away from the substrate 100 to form an epitaxial structure with a stepped step, wherein the stepped step includes an upper mesa and a lower mesa, wherein the upper mesa is the upper surface of the P-GaN layer 250, and the lower mesa is the surface of the N-GaN layer 220 exposed by etching;

[0058] S4, forming an electrode structure on the epitaxial structure, the electrode structure including a first electrode 310 and a second electrode 320, the first electrode 310 is located on the upper table surface, the second electrode 320 is located on the lower table surface, and the second electrode 320 surrounds the circumference of the first electrode 310;

[0059] S5 , forming a passivation layer 400 on the epitaxial structure, wherein the passivation layer 400 covers the stepped steps and the side edges of the electrode structure and exposes the upper surfaces of the first electrode 310 and the second electrode 320 .

[0060] The first electrode 310 is deposited on the upper table by MOCVD method, and is subjected to rapid high temperature annealing, the annealing temperature range is 400 ° C ~ 600 ° C, and the annealing time is 30 seconds ~ 2 minutes, so as to activate the acceptor impurities in the P-GaN layer 250, optimize the injection efficiency of hole carriers, and reduce the contact resistance between the first electrode 310 and the P-GaN layer 250. The second electrode 320 is deposited on the lower table by MOCVD, and is subjected to rapid high temperature annealing, the annealing temperature range is 750 ° C ~ 850 ° C, and the annealing time is 30 seconds ~ 2 minutes, so as to optimize the ohmic contact between the second electrode 320 and the N-GaN layer 220 and reduce the contact resistance between the second electrode 320 and the N-GaN layer 220.

[0061] As an example, the first electrode 310 is a Pd / Au metal stack with a thickness of 50 nm deposited on the surface of the P-GaN layer 250, and the first electrode 310 is subjected to rapid annealing at a temperature of 400°C and an annealing time of 30 seconds. The second electrode 320 is a Ti / Al / Ni / Au metal stack with a thickness of 220 nm deposited on the surface of the N-GaN layer 220, and the second electrode 320 is subjected to rapid high temperature annealing at a temperature of 800°C and an annealing time of 30 seconds.

[0062] It should be noted that the epitaxial stacking layer may be formed by any one or more methods including but not limited to molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) and the like. The passivation layer 400 may be formed by any one or more methods including but not limited to plasma enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD) and the like on the epitaxial structure.

[0063] For details not disclosed in the preparation method of the GaN-based α-particle detector provided in this embodiment, please refer to the details disclosed in the GaN-based α-particle detector in the embodiments of the present application, and no further details will be given here.

[0064] In summary, this embodiment provides a method for preparing a GaN-based α-particle detector. Thanks to the design of the multi-quantum well layer 240, the GaN-based α-particle detector prepared by the method provided by the present application is superior in signal intensity, response speed and energy resolution compared to conventional single GaN structure α-particle detectors or silicon-based α-particle detectors. It also has high dark current suppression capability and excellent radiation resistance, and can work stably for a long time in a complex environment, meeting the high performance requirements of nuclear radiation detection and nuclear safety monitoring.

[0065] In the description of the aforementioned embodiments, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they contradict each other.

[0066] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

Claims

1. A GaN-based α-particle detector for detecting α-particles, characterized in that: include: substrate; An epitaxial structure is located on the substrate; the epitaxial structure includes a multi-quantum well layer, and the multi-quantum well layer is configured to provide a quantum confinement effect to confine carriers corresponding to the incident α particles in the multi-quantum well layer within the multi-quantum well layer, wherein: A stair-shaped step is etched on a side of the epitaxial structure away from the substrate, and the stair-shaped step includes an upper table and a lower table; The alpha particle detector further comprises an electrode structure, wherein the electrode structure comprises a first electrode and a second electrode arranged at intervals, wherein the first electrode is located on the upper table surface, the second electrode is located on the lower table surface, and the second electrode is arranged around the periphery of the first electrode; The first electrode includes a first contact portion and a second contact portion, the first contact portion is a metal thin layer formed on the upper table surface, and the second contact portion is a metal column formed on the first contact portion.

2. The alpha particle detector according to claim 1, characterized in that: The multi-quantum well layer includes a multi-periodic stacked layer structure, and the layer structure includes any one of an AlGaN / GaN stack, an AlGaN / InGaN stack, an AlN / GaN stack, or an InAlN / GaN stack.

3. The alpha particle detector according to claim 2, characterized in that: The number of stacking periods of the multi-periodic stacked layer structure is between 3 and 100 periods.

4. The alpha particle detector according to claim 1, characterized in that: The epitaxial structure also includes a GaN buffer layer, an N-GaN layer, a barrier layer and a P-GaN layer stacked in sequence on the substrate, wherein the multi-quantum well layer is located between the barrier layer and the P-GaN layer.

5. The alpha particle detector according to claim 4, characterized in that: The upper mesa is the upper surface of the P-GaN layer, and the lower mesa is the surface of the N-GaN layer exposed by etching.

6. The alpha particle detector according to claim 1, characterized in that: The electrode structure is composed of a metal material with a high work function, and the electrode structure includes any one of Ni / Au, Pd / Au or Pt / Au metal combinations.

7. The alpha particle detector according to claim 1, characterized in that The thickness of the first contact portion ranges from 5 nm to 20 nm, and the thickness of the second contact portion ranges from 50 nm to 500 nm.

8. A method for preparing a GaN-based α-particle detector, used for preparing the α-particle detector according to any one of claims 1 to 7, characterized in that: include: providing a substrate; Forming an epitaxial stack layer on the substrate, wherein the epitaxial stack layer includes a GaN buffer layer, an N-GaN layer, a barrier layer, a multi-quantum well layer and a P-GaN layer stacked in sequence from bottom to top; Etching is performed on a side of the epitaxial stack layer away from the substrate to form an epitaxial structure with a stepped step, wherein the stepped step includes an upper mesa and a lower mesa, wherein the upper mesa is the upper surface of the P-GaN layer, and the lower mesa is the surface of the N-GaN layer exposed by etching; forming an electrode structure on the epitaxial structure, the electrode structure comprising a first electrode and a second electrode, the first electrode being located on the upper table surface, the second electrode being located on the lower table surface, and the second electrode surrounding a peripheral side of the first electrode; A passivation layer is formed on the epitaxial structure, wherein the passivation layer covers the stepped steps and the side edges of the electrode structure and exposes the upper surfaces of the first electrode and the second electrode respectively.

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