Heterojunction-based aluminum nitride vacuum detector and preparation method thereof

Abstract

The invention provides a heterojunction-based aluminum nitride vacuum detector, which can be applied to the technical field of semiconductors and optoelectronic materials, and comprises a sapphire substrate, an aluminum nitride epitaxial layer, an n-type aluminum gallium nitride layer and an aluminum nitride layer which are sequentially arranged, the first electrode is positioned on one side, far away from the sapphire substrate, of the aluminum nitride layer; the second electrode is positioned on one side, far away from the sapphire substrate, of the n-type aluminum gallium nitride layer; the insulating layer is located on the side, away from the sapphire substrate, of the n-type aluminum gallium nitride layer and located between the aluminum nitride layer and the second electrode, and a heterojunction is formed between the aluminum nitride layer and the n-type aluminum gallium nitride layer. By arranging the n-type aluminum gallium nitride layer with high doping concentration and the undoped aluminum nitride layer, depletion regions are mainly distributed in the aluminum nitride layer, so that the aluminum nitride layer has relatively high electric field intensity, and separation and transportation of current carriers are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductors and optoelectronic materials, and particularly relates to an aluminum nitride vacuum detector based on a heterojunction and a preparation method thereof. Background Art

[0002] Vacuum detectors are used to detect vacuum ultraviolet light with a wavelength range of 120 - 200 nm, and are mainly applied in fields such as space science and astrophysics. Usually, wide-bandgap semiconductor aluminum nitride (AlN) is used as the light absorption medium. Nowadays, AlN-based vacuum ultraviolet detectors are mainly Schottky structures and Metal-Semiconductor-Metal (MSM) structures. The advantages of these two structures include large responsivity, high quantum efficiency, low dark current, low noise, etc. However, these two structures are greatly affected by surface states, and large-area electrodes will seriously affect the absorption of vacuum ultraviolet light, thereby reducing the quantum efficiency. Summary of the Invention

[0003] (I) Technical Problems to be Solved

[0004] To solve at least one of the above problems existing in vacuum detectors in the prior art, embodiments of the present invention provide an aluminum nitride vacuum detector based on a heterojunction and a preparation method thereof. By setting an n-type aluminum gallium nitride layer with a high doping concentration and an undoped aluminum nitride layer, the depletion region is mainly distributed in the aluminum nitride layer, so that there is a high electric field strength in the aluminum nitride layer, which is conducive to the separation and transportation of carriers.

[0005] (II) Technical Solutions

[0006] In view of the above technical problems, embodiments of the present invention propose an aluminum nitride vacuum detector based on a heterojunction and a preparation method thereof.

[0007] According to a first aspect of the present invention, there is provided an aluminum nitride vacuum detector based on a heterojunction, comprising: a sapphire substrate; an aluminum nitride buffer layer located on the sapphire substrate; an aluminum nitride epitaxial layer located on a side of the aluminum nitride buffer layer away from the sapphire substrate; an n-type aluminum gallium nitride layer located on a side of the aluminum nitride epitaxial layer away from the sapphire substrate; an aluminum nitride layer located on a side of the n-type aluminum gallium nitride layer away from the sapphire substrate; a first electrode located on a side of the aluminum nitride layer away from the sapphire substrate; a second electrode located on a side of the n-type aluminum gallium nitride layer away from the sapphire substrate; and an insulating layer located on a side of the n-type aluminum gallium nitride layer away from the sapphire substrate and between the aluminum nitride layer and the second electrode, wherein a heterojunction is formed between the aluminum nitride layer and the n-type aluminum gallium nitride layer.

[0008] In some exemplary embodiments, the doping element in the n-type aluminum gallium nitride layer includes silicon, and the doping concentration is 2×10 18 cm-3 -4×10 18 cm -3 ; The molar ratio of aluminum element to gallium element in the n-type aluminum gallium nitride layer is 6:4.

[0009] In some exemplary embodiments, a Schottky contact is formed between the first electrode and the aluminum nitride layer; and an ohmic contact is formed between the second electrode and the n-type aluminum gallium nitride layer.

[0010] In some exemplary embodiments, the first electrode includes a metal electrode and a bonding pad electrode sequentially arranged along a direction perpendicular to the surface of the sapphire substrate, wherein the area of the metal electrode is larger than that of the bonding pad electrode; the metal electrode includes a nickel layer and a gold layer sequentially arranged along a direction perpendicular to the surface of the sapphire substrate; and the bonding pad electrode includes a titanium layer, an aluminum layer, a titanium layer, and a gold layer sequentially arranged along a direction perpendicular to the surface of the sapphire substrate; the second electrode includes a titanium layer, an aluminum layer, a titanium layer, and a gold layer sequentially arranged along a direction perpendicular to the surface of the sapphire substrate.

[0011] In some exemplary embodiments, the structure of the area of the metal electrode not covered by the bonding pad electrode includes one of a hollow electrode structure, an interdigital electrode structure, or a grid-shaped electrode.

[0012] According to a second aspect of the present invention, a method for preparing a heterojunction-based aluminum nitride vacuum detector is provided, including: preparing a sapphire substrate; sequentially growing an aluminum nitride buffer layer, an aluminum nitride epitaxial layer, an n-type aluminum gallium nitride layer, and an aluminum nitride layer on the sapphire substrate to obtain an epitaxial wafer; fabricating a second electrode on the epitaxial wafer; and fabricating a first electrode on the epitaxial wafer to obtain a heterojunction-based aluminum nitride vacuum detector.

[0013] In some exemplary embodiments, sequentially growing an aluminum nitride buffer layer, an aluminum nitride epitaxial layer, an n-type aluminum gallium nitride layer, and an aluminum nitride layer on the sapphire substrate includes: using trimethylaluminum as an aluminum source and ammonia as a nitrogen source, and using a metal organic chemical vapor deposition device to sequentially grow an aluminum nitride buffer layer and an aluminum nitride epitaxial layer on the sapphire substrate; using trimethylaluminum as an aluminum source, trimethylgallium as a gallium source, and ammonia as a nitrogen source to grow an aluminum gallium nitride layer on the aluminum nitride epitaxial layer; using silane as a silicon source to perform n-type doping on the aluminum gallium nitride layer to obtain an n-type aluminum gallium nitride layer; and growing an aluminum nitride layer on the n-type aluminum gallium nitride layer to obtain an epitaxial wafer.

[0014] In some exemplary embodiments, preparing a second electrode on an epitaxial wafer includes: growing an insulating layer on an aluminum nitride layer; coating a photoresist on the insulating layer; performing a first photolithography process, and obtaining an n-type aluminum gallium nitride layer mesa through exposure, development, etching, and engraving; removing the photoresist and the insulating layer; re-coating the insulating layer and applying a second photoresist; performing a second photolithography process, and etching an n-type ohmic contact window on the n-type aluminum gallium nitride layer mesa; sputtering a titanium layer, an aluminum layer, a titanium layer, and a gold layer on the n-type ohmic contact window to obtain a second electrode; and performing distributed annealing with nitrogen as a protective atmosphere, where the first annealing temperature is 530 °C ± 30 °C and the first annealing time is 300 s ± 30 s; and the second annealing temperature is 900 °C ± 50 °C and the second annealing time is 25 s - 30 s.

[0015] In some exemplary embodiments, preparing a first electrode on an epitaxial wafer includes: applying a third photoresist, and through the third photolithography process, etching a Schottky contact electrode window on the aluminum nitride layer; using an electron beam evaporation coating process to sequentially deposit a transparent electrode nickel layer and a gold layer on the Schottky contact electrode window to obtain a metal electrode in the first electrode; removing the photoresist and the excess metal to obtain a preset electrode pattern; using a mixed gas of oxygen and nitrogen as a protective atmosphere, annealing at a temperature of 500 °C ± 50 °C for 4 min - 6 min; applying a fourth photoresist, and through the fourth photolithography process, etching a bonding electrode window on the metal electrode; and sputtering a titanium layer, an aluminum layer, a titanium layer, and a gold layer on the bonding electrode window to obtain a first electrode.

[0016] In some exemplary embodiments, the doping element in the n-type aluminum gallium nitride layer includes silicon, and the doping concentration is 2×10 18 cm -3 -4×10 18 cm -3 ; the molar ratio of aluminum element to gallium element in the n-type aluminum gallium nitride layer is 6:4.

[0017] (III) Beneficial effects

[0018] As can be seen from the above technical solutions, a heterojunction-based aluminum nitride vacuum detector and a preparation method thereof provided by an embodiment of the present invention have at least the following beneficial effects:

[0019] (1) By setting an n-type aluminum gallium nitride layer with a high doping concentration and an undoped aluminum nitride layer, the depletion region is mainly distributed in the aluminum nitride layer, so that there is a high electric field strength in the aluminum nitride layer, which is beneficial to the separation and transportation of carriers.

[0020] (2) Compared with aluminum nitride vacuum detectors with MSM structures and Schottky structures, the aluminum nitride vacuum detector of the embodiment of the present invention converts the pn junction from in-plane to in-body, greatly reducing the influence of surface states and improving the light reception efficiency.

[0021] (3) A Schottky contact is formed between the aluminum nitride layer and the first electrode. The first electrode is hollowed out or processed into an interdigital electrode or a grid-shaped electrode by using photolithography technology, reducing the absorption of light by the electrode and improving the light reception efficiency, and it is expected to achieve vacuum ultraviolet light detection below 150 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Through the following description of the embodiments of the present invention with reference to the drawings, the above content and other objects, features and advantages of the present invention will become clearer. In the drawings:

[0023] Figure 1 Schematically shows a structural diagram of a heterojunction-based aluminum nitride vacuum detector according to an embodiment of the present invention;

[0024] Figure 2 Schematically shows a first structural diagram of a first electrode according to an embodiment of the present invention;

[0025] Figure 3 Schematically shows a second structural diagram of a first electrode according to an embodiment of the present invention;

[0026] Figure 4 Schematically shows a third structural diagram of a first electrode according to an embodiment of the present invention; and

[0027] Figure 5 Schematically shows a flowchart of a preparation method of a heterojunction-based aluminum nitride vacuum detector according to an embodiment of the present invention.

[0028] REFERENCE SIGNS:

[0029] 1 - Sapphire substrate; 2 - Aluminum nitride buffer layer; 3 - Aluminum nitride epitaxial layer; 4 - n-type aluminum gallium nitride layer; 5 - Aluminum nitride layer; 6 - First electrode; 61 - Metal electrode; 62 - Bonding electrode; 7 - Second electrode; 8 - Insulating layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To make the objects, technical solutions and advantages of the present invention clearer and more understandable, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0031] Figure 1 Schematically shows a structural diagram of a heterojunction-based aluminum nitride vacuum detector according to an embodiment of the present invention.

[0032] As Figure 1As shown, a vacuum detector based on a heterojunction of aluminum nitride according to an embodiment of the present invention includes: a sapphire substrate 1; an aluminum nitride buffer layer 2 located on the sapphire substrate 1; an aluminum nitride epitaxial layer 3 located on the side of the aluminum nitride buffer layer 2 away from the sapphire substrate 1; an n-type aluminum gallium nitride layer 4 located on the side of the aluminum nitride epitaxial layer 3 away from the sapphire substrate 1; an aluminum nitride layer 5 located on the side of the n-type aluminum gallium nitride layer 4 away from the sapphire substrate 1; a first electrode 6 located on the side of the aluminum nitride layer 5 away from the sapphire substrate 1; a second electrode 7 located on the side of the n-type aluminum gallium nitride layer 4 away from the sapphire substrate 1; and an insulating layer 8 located on the side of the n-type aluminum gallium nitride layer 4 away from the sapphire substrate 1 and between the aluminum nitride layer 5 and the second electrode 7, wherein a heterojunction is formed between the aluminum nitride layer 5 and the n-type aluminum gallium nitride layer 4.

[0033] In some exemplary embodiments, the doping element in the n-type aluminum gallium nitride layer 4 includes silicon, and the doping concentration is 2×10 18 cm -3 -4×10 18 cm -3 ; the molar ratio of aluminum to gallium in the n-type aluminum gallium nitride layer 4 is 6:4. By setting the highly doped n-type aluminum gallium nitride layer 4 and the undoped aluminum nitride layer 5, the depletion region is mainly distributed in the aluminum nitride layer 5, resulting in a high electric field strength in the aluminum nitride layer 5, which is beneficial to the separation and transportation of carriers. Compared with the aluminum nitride vacuum detectors of the MSM structure and the Schottky structure, the aluminum nitride vacuum detector of the embodiment of the present invention converts the pn junction from in-plane to in-body, greatly reducing the influence of surface states and improving the light reception efficiency.

[0034] In the embodiment of the present invention, a Schottky contact is formed between the first electrode 6 and the aluminum nitride layer 5; and an ohmic contact is formed between the second electrode 7 and the n-type aluminum gallium nitride layer 4.

[0035] In some exemplary embodiments, the first electrode 6 includes a metal electrode 61 and a bonding electrode 62 arranged in sequence along the direction perpendicular to the surface of the sapphire substrate 1, wherein the area of the metal electrode 61 is larger than that of the bonding electrode 62; the metal electrode 61 includes a nickel layer and a gold layer arranged in sequence along the direction perpendicular to the surface of the sapphire substrate 1. Preferably, the thicknesses of each layer are 10 nm and 10 nm respectively; and the bonding electrode 62 includes a titanium layer, an aluminum layer, a titanium layer, and a gold layer (Ti / Al / Ti / Au) arranged in sequence along the direction perpendicular to the surface of the sapphire substrate 1. Preferably, the thicknesses of each layer are 15 nm, 250 nm, 50 nm, and 150 nm respectively; the second electrode 7 includes a titanium layer, an aluminum layer, a titanium layer, and a gold layer arranged in sequence along the direction perpendicular to the surface of the sapphire substrate 1, and preferably, the thicknesses of each layer are 15 nm, 250 nm, 50 nm, and 150 nm respectively.

[0036] Preferably, the structure of the region where the metal electrode 61 is not covered by the bonding electrode 62 includes one of a hollowed electrode structure, an interdigital electrode structure, or a grid-shaped electrode. Please refer to Figure 2 , Figure 3 and Figure 4 respectively. Through the design of the first electrode 6 structure, the absorption of light by the electrode is reduced, and the light reception efficiency is improved. It is expected to achieve vacuum ultraviolet light detection below 150 nm.

[0037] Figure 5 FIG. schematically shows a flowchart of a method for preparing a heterojunction-based aluminum nitride vacuum detector according to an embodiment of the present invention.

[0038] As Figure 5 shown, a method for preparing a heterojunction-based aluminum nitride vacuum detector according to an embodiment of the present invention includes steps S110-S140.

[0039] In step S110, a sapphire substrate 1 is prepared.

[0040] In step S120, an aluminum nitride buffer layer 2, an aluminum nitride epitaxial layer 3, an n-type aluminum gallium nitride layer 4, and an aluminum nitride layer 5 are sequentially grown on the sapphire substrate 1 to obtain an epitaxial wafer.

[0041] For example, using trimethylaluminum as the aluminum source and ammonia as the nitrogen source, an aluminum nitride buffer layer 2 and an aluminum nitride epitaxial layer 3 are sequentially grown on the sapphire substrate 1 using a metalorganic chemical vapor deposition equipment; using trimethylaluminum as the aluminum source, trimethylgallium as the gallium source, and ammonia as the nitrogen source, an aluminum gallium nitride layer is grown on the aluminum nitride epitaxial layer 3; using silane as the silicon source, the aluminum gallium nitride layer is n-type doped to obtain an n-type aluminum gallium nitride layer 4; an aluminum nitride layer 5 is grown on the n-type aluminum gallium nitride layer 4 to obtain an epitaxial wafer, wherein the doping element in the n-type aluminum gallium nitride layer 4 includes silicon, and the doping concentration is 2×10 18 cm -3 -4×10 18 cm -3 ; the molar ratio of aluminum element to gallium element in the n-type aluminum gallium nitride layer 4 is 6:4; the thickness of the aluminum nitride layer 5 can be 300 nm.

[0042] In step S130, a second electrode 7 is fabricated on the epitaxial wafer.

[0043] For example, an insulating layer is grown on the aluminum nitride layer 5; photoresist is coated on the insulating layer; for the first photolithography, after exposure, development, etching, and engraving, a mesa of the n-type aluminum gallium nitride layer 4 is obtained; the photoresist and the insulating layer are removed; the insulating layer is re-covered and the second photoresist is coated; for the second photolithography, an n-type ohmic contact window is etched on the mesa of the n-type aluminum gallium nitride layer 4; a titanium layer, an aluminum layer, a titanium layer, and a gold layer are sputtered on the n-type ohmic contact window to obtain the second electrode 7; and distributed annealing is performed with nitrogen as the protective atmosphere, the first annealing temperature is 530 °C plus or minus 30 °C, and the first annealing time is 300 s ± 30 s; and the second annealing temperature is 900 °C ± 50 °C, and the second annealing time is 25 s - 30 s. The material of the insulating layer can be silicon dioxide.

[0044] In step S140, a first electrode 6 is prepared on the epitaxial wafer to obtain a heterojunction-based aluminum nitride vacuum detector.

[0045] For example, the third photoresist is coated, and through the third photolithography, a Schottky contact electrode window is etched on the aluminum nitride layer 5; using the electron beam evaporation coating process, a transparent electrode nickel layer and a gold layer are sequentially evaporated on the Schottky contact electrode window to obtain the metal electrode 61 in the first electrode 6; the photoresist and the excess metal are removed to obtain a preset electrode pattern; with a mixed gas of oxygen and nitrogen as the protective atmosphere, annealing is performed at a temperature of 500 °C ± 50 °C for 4 min - 6 min; the fourth photoresist is coated, and through the fourth photolithography, a bonding electrode window is etched on the metal electrode 61; and a titanium layer, an aluminum layer, a titanium layer, and a gold layer are sputtered on the bonding electrode window to obtain the first electrode 6.

[0046] Example 1: A preparation method of a vacuum ultraviolet detector based on an aluminum nitride n-type aluminum gallium nitride heterojunction.

[0047] (1) Epitaxial wafer growth: Trimethylaluminum (TMAl) and trimethylgallium (TMGa) are respectively used as metal sources, ammonia (NH3) is used as the N source, and silane (SiH4) is used as the Si source. A high-quality aluminum nitride epitaxial wafer is grown on the sapphire substrate 1 in turn by a metal-organic chemical vapor deposition (MOCVD) device, including an aluminum nitride buffer layer 2 and an aluminum nitride epitaxial layer 3. Then, an n-type aluminum gallium nitride layer 4 is grown on the aluminum nitride epitaxial wafer, where the Al component is 60%, and Si is used as a dopant to achieve n-type doping, and the electron concentration is 3×10 18 cm -3 . Finally, a layer of aluminum nitride layer 5 about 300 nm thick is grown to complete the preparation of the epitaxial wafer.

[0048] (2) Process preparation: After cleaning the epitaxial wafer, silicon dioxide (SiO 2), an insulating layer and photoresist are applied. For the first photolithography, after exposure and development, SiO 2 etching is carried out, and the mesa of the n-type aluminum gallium nitride layer 4 is etched out by inductively coupled plasma (ICP). The photoresist is removed, and SiO 2 is applied again, and SiO 2 insulating layer is covered. Photoresist is applied for the second photolithography, and the n-type ohmic contact window is etched out. Ti / Al / Ti / Au is sputtered with thicknesses of 15nm / 250nm / 50nm / 150nm respectively. The photoresist and the excess metal are removed to obtain the second electrode 7. In an N 2 atmosphere, one-step annealing is carried out at 530 °C for 300 s, and two-step annealing is carried out at 900 °C for 30 s. Photoresist is applied, and for the third photolithography, the p-pole Schottky electrode window is etched out. 10nm Ni and 10nm Au are successively evaporated by an electron beam evaporation coating machine to obtain the metal electrode 61. The photoresist and the excess metal are removed. After the photoresist is removed, a specific electrode pattern is obtained. In an O 2 and N 2 mixed atmosphere, annealing is carried out at 500 °C for 5 min. Photoresist is applied for the fourth photolithography, and the window of the bonding electrode 62 of the Schottky electrode is etched out. Ti / Al / Ti / Au is sputtered with thicknesses of 15nm / 250nm / 50nm / 150nm respectively to obtain the bonding electrode 62. The photoresist and the excess metal are removed. In the embodiment of the present invention, the size of each device is 350μm×350μm.

[0049] In the above specific embodiments, the purpose, technical solution and beneficial effects of the present invention are further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An aluminum nitride vacuum detector based on heterojunction, characterized in that: include: Sapphire substrate; An aluminum nitride buffer layer, located on the sapphire substrate; An aluminum nitride epitaxial layer, located on a side of the aluminum nitride buffer layer away from the sapphire substrate; An n-type aluminum gallium nitride layer is located on a side of the aluminum nitride epitaxial layer away from the sapphire substrate; An aluminum nitride layer, located on a side of the n-type aluminum gallium nitride layer away from the sapphire substrate; A first electrode, located on a side of the aluminum nitride layer away from the sapphire substrate; A second electrode is located on a side of the n-type aluminum gallium nitride layer away from the sapphire substrate; as well as an insulating layer, located on a side of the n-type aluminum gallium nitride layer away from the sapphire substrate and between the aluminum nitride layer and the second electrode, Wherein, a heterojunction is formed between the aluminum nitride layer and the n-type aluminum gallium nitride layer.

2. The aluminum nitride vacuum detector based on heterojunction according to claim 1, characterized in that: The doping element in the n-type aluminum gallium nitride layer includes silicon element, and the doping concentration is 2×10 18 cm -3 -4×10 18 cm -3 ; The molar ratio of aluminum element to gallium element in the n-type aluminum gallium nitride layer is 6:

4.

3. The aluminum nitride vacuum detector based on heterojunction according to claim 1, characterized in that: A Schottky contact is formed between the first electrode and the aluminum nitride layer; and An ohmic contact is formed between the second electrode and the n-type aluminum gallium nitride layer.

4. The aluminum nitride vacuum detector based on heterojunction according to claim 1, characterized in that: The first electrode comprises a metal electrode and a pressure welding electrode sequentially arranged in a direction perpendicular to the surface of the sapphire substrate, wherein the area of ​​the metal electrode is larger than the area of ​​the pressure welding electrode; the metal electrode comprises a nickel layer and a gold layer sequentially arranged in a direction perpendicular to the surface of the sapphire substrate; and the pressure welding electrode comprises a titanium layer, an aluminum layer, a titanium layer and a gold layer sequentially arranged in a direction perpendicular to the surface of the sapphire substrate; The second electrode includes a titanium layer, an aluminum layer, a titanium layer and a gold layer which are sequentially arranged in a direction perpendicular to the surface of the sapphire substrate.

5. The aluminum nitride vacuum detector based on heterojunction according to claim 4, characterized in that: The structure of the area of ​​the metal electrode not covered by the pressure welding electrode includes one of a hollow electrode structure, an interdigitated structure electrode or a gate electrode.

6. A method for preparing an aluminum nitride vacuum detector based on a heterojunction, characterized in that: The method comprises: Preparing a sapphire substrate; An aluminum nitride buffer layer, an aluminum nitride epitaxial layer, an n-type aluminum gallium nitride layer, and an aluminum nitride layer are sequentially grown on the sapphire substrate to obtain an epitaxial wafer; preparing a second electrode on the epitaxial wafer; and A first electrode is prepared on the epitaxial wafer to obtain an aluminum nitride vacuum detector based on a heterojunction.

7. The preparation method according to claim 6, characterized in that: The sequentially growing an aluminum nitride buffer layer, an aluminum nitride epitaxial layer, an n-type aluminum gallium nitride layer, and an aluminum nitride layer on the sapphire substrate comprises: Using trimethylaluminum as an aluminum source and ammonia as a nitrogen source, using metal organic chemical vapor deposition equipment, an aluminum nitride buffer layer and an aluminum nitride epitaxial layer are sequentially grown on a sapphire substrate; growing an aluminum gallium nitride layer on the aluminum nitride epitaxial layer using trimethylaluminum as an aluminum source, trimethylgallium as a gallium source, and ammonia as a nitrogen source; Using monosilane as a silicon source, performing n-type doping on the aluminum gallium nitride layer to obtain an n-type aluminum gallium nitride layer; An aluminum nitride layer is grown on the n-type aluminum gallium nitride layer to obtain an epitaxial wafer.

8. The preparation method according to claim 6, characterized in that: The step of preparing the second electrode on the epitaxial wafer comprises: growing an insulating layer on the aluminum nitride layer; Applying photoresist on the insulating layer; The first photolithography, after exposure, development, corrosion and etching, obtains the n-type aluminum gallium nitride layer table; Removing photoresist and insulating layers; Re-cover the insulating layer and apply the photoresist for the second time; A second photolithography process is to etch an n-type ohmic contact window on the n-type aluminum gallium nitride layer mesa; sputtering a titanium layer, an aluminum layer, a titanium layer and a gold layer on the n-type ohmic contact window to obtain a second electrode; and Distributed annealing is performed with nitrogen as the protective atmosphere, the first step annealing temperature is 530°C plus or minus 30°C, the first step annealing time is 300s±30s; and the second step annealing temperature is 900°C±50°C, and the second step annealing time is 25s-30s.

9. The preparation method according to claim 8, characterized in that: The step of preparing a first electrode on the epitaxial wafer comprises: Applying a third photoresist, and etching a Schottky contact electrode window on the aluminum nitride layer through a third photolithography; By using an electron beam evaporation coating process, a transparent electrode nickel layer and a gold layer are sequentially evaporated on the Schottky contact electrode window to obtain a metal electrode in the first electrode; Remove the photoresist and excess metal to obtain a preset electrode pattern; Anneal for 4-6 minutes at 500°C ± 50°C with a mixture of oxygen and nitrogen as the protective atmosphere; Applying a fourth photoresist, and etching a bonding electrode window on the metal electrode through a fourth photolithography; and A titanium layer, an aluminum layer, a titanium layer and a gold layer are sputtered on the pressure welding electrode window to obtain a first electrode.

10. The preparation method according to claim 6, characterized in that: The doping element in the n-type aluminum gallium nitride layer includes silicon element, and the doping concentration is 2×10 18 cm -3 -4×10 18 cm -3 ; The molar ratio of aluminum element to gallium element in the n-type aluminum gallium nitride layer is 6:4.

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