Epitaxial wafer based on sapphire substrate and growth method

Abstract

The invention relates to the technical field of epitaxial wafers, and discloses an epitaxial wafer based on a sapphire substrate and a growth method, an AlN thin film layer, an AlN growth layer, an AlGaN buffer layer, a GaN buffer layer, a GaN channel layer, an AlN spacing layer, an AlGaN barrier layer and a GaN cap layer are sequentially arranged on the top surface of the sapphire substrate of the epitaxial wafer from bottom to top; for the epitaxial wafer, the AlN thin film layer is arranged, so that the epitaxial wafer can grow more smoothly; by arranging the AlN growth layer, oxygen in a substrate material can be prevented from diffusing into the structure, so that impurities are prevented from being formed, and the voltage endurance capability of the device can be improved due to relatively high potential barrier energy; by arranging the AlGaN buffer layer and the GaN buffer layer, lattice mismatch and stress release between AlN and GaN can be reduced, and the high-temperature GaN channel layer can be better grown on the surface of the AlN growth layer; due to the structural design of the epitaxial wafer, two-dimensional growth of GaN can be directly carried out, a thin epitaxial film can be obtained, and the low warping degree of the epitaxial wafer is achieved; the surface of the finally obtained epitaxial layer is flat, which is beneficial to the uniformity of the device and the manufacturing of a back-end chip.

Description

Technical Field

[0001] The invention relates to the technical field of epitaxial wafers, and in particular to an epitaxial wafer based on a sapphire substrate and a growth method thereof. Background Art

[0002] Currently, lateral GaN power devices fabricated with HEMTs on silicon substrates have provided commercial transistors with operating voltages up to 650 V. However, moving to higher voltages, such as 1200 V on GaN-on-Si platforms, lateral GaN power devices require the use of very thick buffer layers, on the order of about 10-12 μm, which significantly increases costs and processing challenges.

[0003] Among substrate materials, the insulating properties of sapphire substrates help extend the voltage rating of GaN HEMTs to 1200V and above while using thinner buffer layers than GaN on Si to achieve similar voltages.

[0004] However, due to lattice mismatch and thermal mismatch, the growth of GaN on sapphire will result in a large bow (warpage value) of the final epitaxial wafer. Generally, a 3um thick GaN film layer is grown on sapphire in two steps, and its bow is about +30um. When it grows to a 6um thick GaN film layer, its bow will increase to about +120um. The larger bow of the epitaxial wafer will be detrimental to the subsequent chip process. Therefore, how to reasonably design a thinner buffer layer and control the epitaxial wafer bow value within ±25um is particularly important for the epitaxial growth of GaN lateral devices based on sapphire substrates. Summary of the invention

[0005] In view of the shortcomings of the background technology, the present invention provides an epitaxial wafer based on a sapphire substrate and a growth method, and the technical problem to be solved is that the warpage value of the existing epitaxial wafer based on a sapphire substrate is relatively large.

[0006] To solve the above technical problems, in a first aspect, the present invention provides the following technical solutions: an epitaxial wafer based on a sapphire substrate, wherein an AlN thin film layer, an AlN growth layer, an AlGaN buffer layer, a GaN buffer layer, a GaN channel layer, an AlN spacer layer, an AlGaN barrier layer and a GaN cap layer are sequentially arranged on the top surface of the sapphire substrate from bottom to top.

[0007] In certain embodiments of the first aspect, the size of the sapphire substrate is 2 inches, 4 inches, 6 inches or 8 inches.

[0008] In certain implementations of the first aspect, the Al component in the AlGaN barrier layer is between 15% and 25%.

[0009] In a certain embodiment of the first aspect, the thickness of the AlN thin film layer is between 10nm and 20nm; the thickness of the AlN growth layer is between 5nm and 15nm; the thickness of the AlGaN buffer layer is between 10nm and 20nm; the thickness of the GaN buffer layer is between 10nm and 20nm; the thickness of the GaN channel layer is between 200nm and 300nm; the thickness of the AlN spacer layer is between 1nm and 1.5nm; the thickness of the AlGaN barrier layer is between 20nm and 25nm; and the thickness of the GaN cap layer is between 2nm and 5nm.

[0010] In a second aspect, the present invention provides a method for growing an epitaxial wafer based on a sapphire substrate, comprising the following steps:

[0011] S1: growing AlN thin film layer on sapphire substrate;

[0012] S2: In an MOCVD reactor, an AlN growth layer, an AlGaN buffer layer, a GaN buffer layer, a GaN channel layer, an AlN spacer layer, an AlGaN barrier layer and a GaN cap layer are sequentially grown on the AlN thin film layer.

[0013] In a certain embodiment of the second aspect, the thickness of the AlN thin film layer produced in step S1 is between 10nm and 20nm; the thickness of the AlN growth layer produced in step S2 is between 5nm and 15nm; the thickness of the AlGaN buffer layer produced in step S2 is between 10nm and 20nm; the thickness of the GaN buffer layer produced in step S2 is between 10nm and 20nm; the thickness of the GaN channel layer produced in step S2 is between 200nm and 300nm; the thickness of the AlN spacer layer produced in step S2 is between 1nm and 1.5nm; the thickness of the AlGaN barrier layer produced in step S2 is between 20nm and 25nm; the thickness of the GaN cap layer produced in step S2 is between 2nm and 5nm.

[0014] In a certain embodiment of the second aspect, the Al composition of the AlGaN barrier layer manufactured in step S2 is between 15% and 25%.

[0015] In certain embodiments of the second aspect, the size of the sapphire substrate in step S1 is 2 inches, 4 inches, 6 inches or 8 inches.

[0016] In a certain implementation manner of the second aspect, the process of making the AlN thin film layer in step S1 is as follows:

[0017] The AlN thin film layer is formed on the sapphire substrate by a PVD sputtering method, and the temperature of the formation is set between 500 degrees Celsius and 550 degrees Celsius.

[0018] In a certain implementation manner of the second aspect, the process of making the AlN growth layer in step S2 is as follows:

[0019] In the MOCVD reactor, the temperature is first raised to 1050 degrees Celsius to perform high-temperature treatment on the sapphire substrate for 2 minutes, and H2 is introduced, wherein the flow rate of H2 is between 120L and 180L;

[0020] Then, before the growth, 5-10S of trimethylaluminum is introduced into the MOCVD reactor, wherein the flow rate of trimethylaluminum is 50-100 sccm;

[0021] Then, H2, NH3 and trimethylaluminum are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of NH3 is between 1 and 2 L, the flow rate of trimethylaluminum is between 100 and 200 sccm, and the temperature is set between 1000 and 1050 degrees Celsius;

[0022] The process of making the AlGaN buffer layer in step S2 is as follows:

[0023] The temperature of the MOCVD reactor is set between 900 and 950 degrees Celsius, and H2, NH3, trimethylaluminum and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of NH3 is between 5 and 10 L, the flow rate of trimethylaluminum is between 200 and 400 sccm, and the flow rate of trimethylgallium is between 20 and 100 sccm;

[0024] The process of making the GaN buffer layer in step S2 is as follows:

[0025] N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 5 and 20 L, and the flow rate of trimethylgallium is between 200 and 400 sccm;

[0026] The process of making the GaN channel layer in step S2 is as follows:

[0027] The temperature of the MOCVD reactor is set between 1000 and 1050 degrees Celsius, and N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 20 and 50 L, and the flow rate of trimethylgallium is between 200 and 400 sccm;

[0028] The process of making the AlN spacer layer in step S2 is as follows:

[0029] The temperature of the MOCVD reactor is set between 1050 and 1100 degrees Celsius, and H2 and trimethylaluminum are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, and the flow rate of trimethylaluminum is between 100 and 200 sccm;

[0030] The process of making the AlGaN barrier layer in step S2 is as follows:

[0031] The temperature of the MOCVD reactor is set between 1000 and 1050 degrees Celsius, and H2, trimethylaluminum and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of trimethylaluminum is between 300 and 500 sccm, and the flow rate of trimethylgallium is between 100 and 200 sccm;

[0032] The process of making the GaN cap layer in step S2 is as follows:

[0033] The temperature of the MOCVD reactor is set between 1050 and 1100 degrees Celsius, and N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 20 and 50 L, and the flow rate of trimethylgallium is between 200 and 400 sccm.

[0034] Compared with the prior art, the present invention has the following beneficial effects: for the epitaxial wafer of the present invention, by providing the AlN thin film layer, it is beneficial for the epitaxial wafer to grow more smoothly;

[0035] The AlN growth layer can prevent oxygen in the substrate material from diffusing into the structure, thereby avoiding the formation of impurities. Its higher potential barrier can increase the device's withstand voltage. In addition, a two-dimensional GaN layer can be grown on its surface, directly skipping the low-temperature GaN growth and three-dimensional to two-dimensional GaN growth required by the traditional two-step method of growing GaN on sapphire, thereby improving device leakage.

[0036] By providing the AlGaN buffer layer and the GaN buffer layer, not only can the lattice mismatch between AlN and GaN be reduced, but also the stress can be released to a certain extent, so that the high-temperature GaN channel layer can be better grown on the surface of the AlN growth layer;

[0037] Finally, the structural design of the epitaxial wafer of the present invention enables GaN to be directly grown in two dimensions, so that a thinner epitaxial wafer film can be obtained, and a low warpage of the epitaxial wafer can be achieved; and the surface of the obtained epitaxial layer is smooth, which is beneficial to the uniformity of the device and the subsequent chip production; at the same time, this design growth can obtain an epitaxial wafer with higher crystal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1is a schematic structural diagram of the epitaxial wafer in Example 1;

[0039] Figure 2 This is a growth flow chart of the epitaxial wafer in the second embodiment. DETAILED DESCRIPTION

[0040] The illustrative embodiments of the present application include, but are not limited to, an epitaxial wafer based on a sapphire substrate and a growth method.

[0041] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0042] The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in this article refers to and includes any or all possible combinations of one or more associated listed items. "Include" or "include" and similar words mean that the elements or objects appearing in front of "include" or "include" cover the elements or objects listed after "include" or "include" and their equivalents, and do not exclude other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, and can include electrical connections, whether direct or indirect.

[0043] It should be understood that although the terms first, second, third, etc. may be used in the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0044] Embodiment 1

[0045] like Figure 1As shown, an epitaxial wafer based on a sapphire substrate, wherein an AlN thin film layer 2, an AlN growth layer 3, an AlGaN buffer layer 4, a GaN buffer layer 5, a GaN channel layer 6, an AlN spacer layer 7, an AlGaN barrier layer 8 and a GaN cap layer 9 are sequentially arranged on the top surface of the sapphire substrate 1 from bottom to top.

[0046] Specifically, in this embodiment, the size of the sapphire substrate 1 is 2 inches, 4 inches, 6 inches or 8 inches.

[0047] Specifically, in this embodiment, the Al component in the AlGaN barrier layer 8 is between 15% and 25%, and illustratively, may be 18%, 20% or 22%.

[0048] Specifically, in this embodiment, the thickness of the AlN thin film layer 2 is between 10 nm and 20 nm, and illustratively, may be 12 nm, 14 nm, 16 nm or 18 nm.

[0049] For the epitaxial wafer in this embodiment, the epitaxial wafer can be grown more flat by providing the AlN thin film layer 2. In addition, if the thickness of the AlN thin film layer 2 is too thin, it will not work, and if the thickness is too thick, the crystal quality will deteriorate, so the thickness of the AlN thin film layer 2 is between 10nm and 20nm.

[0050] Specifically, in this embodiment, the thickness of the AlN growth layer 3 is between 5 nm and 15 nm, and may be 7 nm, 9 nm, 11 nm or 13 nm, for example.

[0051] For the epitaxial wafer in this embodiment, by setting an AlN growth layer 3, oxygen in the sapphire substrate 1 material can be prevented from diffusing into the structure, thereby avoiding the formation of impurities. Its higher potential barrier can increase the voltage resistance of the device. In addition, a two-dimensional GaN layer can be grown on its surface, directly skipping the low-temperature GaN growth and three-dimensional to two-dimensional GaN growth required for the traditional two-step method of growing GaN on sapphire, thereby improving device leakage.

[0052] Specifically, in this embodiment, the thickness of the AlGaN buffer layer 4 is between 10 nm and 20 nm, and illustratively, may be 12 nm, 14 nm, 16 nm or 18 nm.

[0053] Specifically, in this embodiment, the thickness of the GaN buffer layer 5 is between 10 nm and 20 nm, and illustratively, may be 12 nm, 14 nm, 16 nm or 18 nm.

[0054] The AlGaN buffer layer 4 and the GaN buffer layer 5 in this embodiment can not only reduce the lattice mismatch between AlN and GaN, but also release stress to a certain extent. In addition, if the thickness of the AlGaN buffer layer 4 and the GaN buffer layer 5 is too thin, it will not play a good role. If the thickness is too thick, the crystal quality will deteriorate. Therefore, the thickness of the AlGaN buffer layer 4 and the GaN buffer layer 5 is between 10nm and 20nm.

[0055] Specifically, in this embodiment, the thickness of the GaN channel layer 6 is between 200 nm and 300 nm, and illustratively, may be 220 nm, 240 nm, 260 nm or 280 nm.

[0056] For the epitaxial wafer in this embodiment, the function of the GaN channel layer 6 is to form a polarization effect with the subsequent AlGaN barrier layer 8 to generate spontaneous 2DEG (two-dimensional electron gas). The thickness of this layer matches the thickness of the AlGaN barrier layer 8 and the Al component, and a higher carrier mobility can be obtained.

[0057] Specifically, in this embodiment, the thickness of the AlN spacer layer 7 is between 1 nm and 1.5 nm, and illustratively, may be 1.2 nm or 1.4 nm.

[0058] For the AlN spacer layer 7 in this embodiment, the thickness thereof is set between 1 nm and 1.5 nm, which can reduce the on-resistance Ron of the device while maintaining a good threshold voltage Vth.

[0059] Specifically, in this embodiment, the thickness of the AlGaN barrier layer 8 is between 20 nm and 25 nm, and illustratively, may be 22 nm or 24 nm.

[0060] For the AlGaN barrier layer 8 in this embodiment, its layer thickness and Al composition are designed to obtain a higher carrier concentration and a higher carrier mobility.

[0061] Specifically, in this embodiment, the thickness of the GaN cap layer 9 is between 2 nm and 5 nm, and illustratively, may be 3 nm or 4 nm.

[0062] In actual use, the GaN cap layer 9 can be provided to protect the epitaxial wafer.

[0063] In summary, for the epitaxial wafer of the present invention, by providing the AlN thin film layer 2, it is beneficial for the epitaxial wafer to grow more flat;

[0064] By setting the AlN growth layer 3, oxygen in the substrate material can be prevented from diffusing into the structure to avoid the formation of impurities, and its higher potential barrier can increase the voltage resistance of the device; in addition, a two-dimensional GaN layer can be grown on its surface, directly skipping the low-temperature GaN growth and three-dimensional to two-dimensional GaN growth required by the traditional two-step method of growing GaN on sapphire, thereby improving device leakage;

[0065] By providing the AlGaN buffer layer 4 and the GaN buffer layer 5, not only can the lattice mismatch between AlN and GaN be reduced, but also the stress can be released to a certain extent, so that the high-temperature GaN channel layer can be better grown on the surface of the AlN growth layer 3;

[0066] Finally, the structural design of the epitaxial wafer of the present invention enables GaN to be directly grown in two dimensions, so that a thinner epitaxial wafer film can be obtained, and a low warpage of the epitaxial wafer can be achieved; and the surface of the obtained epitaxial layer is smooth, which is beneficial to the uniformity of the device and the subsequent chip production; at the same time, this design growth can obtain an epitaxial wafer with higher crystal quality.

[0067] In addition, during actual growth, the bow value of the epitaxial wafer of the present invention is within ±25 um, which is beneficial to subsequent process manufacturing.

[0068] Embodiment 2

[0069] like Figure 2 As shown, this embodiment provides a method for growing an epitaxial wafer based on a sapphire substrate, comprising the following steps:

[0070] S1: growing an AlN thin film layer 2 on a sapphire substrate 1 .

[0071] In step S1 , the size of the sapphire substrate 1 is 2 inches, 4 inches, 6 inches or 8 inches.

[0072] In addition, in step S1, the process of making the AlN thin film layer 2 is as follows:

[0073] The AlN thin film layer 2 is formed on the sapphire substrate 1 by a PVD sputtering method, and the forming temperature is set between 500 degrees Celsius and 550 degrees Celsius.

[0074] S2: In an MOCVD reactor, an AlN growth layer 3, an AlGaN buffer layer 4, a GaN buffer layer 5, a GaN channel layer 6, an AlN spacer layer 7, an AlGaN barrier layer 8 and a GaN cap layer 9 are sequentially grown on the AlN thin film layer 2.

[0075] Specifically, in this embodiment, the thickness of the AlN thin film layer 2 produced in step S1 is between 10nm and 20nm; the thickness of the AlN growth layer 3 produced in step S2 is between 5nm and 15nm; the thickness of the AlGaN buffer layer 4 produced in step S2 is between 10nm and 20nm; the thickness of the GaN buffer layer 5 produced in step S2 is between 10nm and 20nm; the thickness of the GaN channel layer 6 produced in step S2 is between 200nm and 300nm; the thickness of the AlN spacer layer 7 produced in step S2 is between 1nm and 1.5nm; the thickness of the AlGaN barrier layer 8 produced in step S2 is between 20nm and 25nm; the thickness of the GaN cap layer 9 produced in step S2 is between 2nm and 5nm.

[0076] For the thickness settings of the AlN growth layer 3, AlGaN buffer layer 4, GaN buffer layer 5, GaN channel layer 6, AlN spacer layer 7, AlGaN barrier layer 8 and GaN cap layer 9 in this embodiment, the specific functions refer to the first embodiment and will not be described here.

[0077] Specifically, in this embodiment, the Al composition of the AlGaN barrier layer manufactured in step S2 is between 15% and 25%.

[0078] Specifically, in this embodiment, the process of making the AlN growth layer 3 in step S2 is as follows:

[0079] In the MOCVD reactor, the temperature is first raised to 1050 degrees Celsius to perform high temperature treatment on the sapphire substrate 1 for 2 minutes, and H2 is introduced, wherein the flow rate of H2 is between 120L and 180L;

[0080] Then, before the growth, 5-10S of trimethylaluminum is introduced into the MOCVD reactor, wherein the flow rate of trimethylaluminum is 50-100 sccm;

[0081] Then, H2, NH3 and trimethylaluminum are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of NH3 is between 1 and 2 L, the flow rate of trimethylaluminum is between 100 and 200 sccm, and the temperature is set between 1000 and 1050 degrees Celsius;

[0082] The process of making the AlGaN buffer layer 4 in step S2 is as follows:

[0083] The temperature of the MOCVD reactor is set between 900 and 950 degrees Celsius, and H2, NH3, trimethylaluminum and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of NH3 is between 5 and 10 L, the flow rate of trimethylaluminum is between 200 and 400 sccm, and the flow rate of trimethylgallium is between 20 and 100 sccm;

[0084] The process of making the GaN buffer layer 5 in step S2 is as follows:

[0085] N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 5 and 20 L, and the flow rate of trimethylgallium is between 200 and 400 sccm;

[0086] The process of making the GaN channel layer 6 in step S2 is as follows:

[0087] The temperature of the MOCVD reactor is set between 1000 and 1050 degrees Celsius, and N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 20 and 50 L, and the flow rate of trimethylgallium is between 200 and 400 sccm;

[0088] The process of making the AlN spacer layer 7 in step S2 is as follows:

[0089] The temperature of the MOCVD reactor is set between 1050 and 1100 degrees Celsius, and H2 and trimethylaluminum are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, and the flow rate of trimethylaluminum is between 100 and 200 sccm;

[0090] The process of making the AlGaN barrier layer 8 in step S2 is as follows:

[0091] The temperature of the MOCVD reactor is set between 1000 and 1050 degrees Celsius, and H2, trimethylaluminum and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of trimethylaluminum is between 300 and 500 sccm, and the flow rate of trimethylgallium is between 100 and 200 sccm;

[0092] The process of making the GaN cap layer 9 in step S2 is as follows:

[0093] The temperature of the MOCVD reactor is set between 1050 and 1100 degrees Celsius, and N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 20 and 50 L, and the flow rate of trimethylgallium is between 200 and 400 sccm.

[0094] The above is based on the present invention as an inspiration. Through the above description, relevant staff can make various changes and modifications without departing from the technical idea of ​​this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. An epitaxial wafer based on a sapphire substrate, characterized in that: The top surface of the sapphire substrate is provided with an AlN thin film layer, an AlN growth layer, an AlGaN buffer layer, a GaN buffer layer, a GaN channel layer, an AlN spacer layer, an AlGaN barrier layer and a GaN cap layer in sequence from bottom to top.

2. The epitaxial wafer based on a sapphire substrate according to claim 1, characterized in that: The size of the sapphire substrate is 2 inches, 4 inches, 6 inches or 8 inches.

3. The epitaxial wafer based on a sapphire substrate according to claim 1, characterized in that: The Al component in the AlGaN barrier layer is between 15% and 25%.

4. An epitaxial wafer based on a sapphire substrate according to any one of claims 1 to 3, characterized in that: The thickness of the AlN thin film layer is between 10nm and 20nm; the thickness of the AlN growth layer is between 5nm and 15nm; the thickness of the AlGaN buffer layer is between 10nm and 20nm; the thickness of the GaN buffer layer is between 10nm and 20nm; the thickness of the GaN channel layer is between 200nm and 300nm; the thickness of the AlN spacer layer is between 1nm and 1.5nm; the thickness of the AlGaN barrier layer is between 20nm and 25nm; and the thickness of the GaN cap layer is between 2nm and 5nm.

5. A method for growing an epitaxial wafer based on a sapphire substrate, characterized in that: The following steps are involved: S1: growing AlN thin film layer on sapphire substrate; S2: In an MOCVD reactor, an AlN growth layer, an AlGaN buffer layer, a GaN buffer layer, a GaN channel layer, an AlN spacer layer, an AlGaN barrier layer and a GaN cap layer are sequentially grown on the AlN thin film layer.

6. The method for growing an epitaxial wafer based on a sapphire substrate according to claim 5, characterized in that: The thickness of the AlN thin film layer produced in step S1 is between 10nm and 20nm; the thickness of the AlN growth layer produced in step S2 is between 5nm and 15nm; the thickness of the AlGaN buffer layer produced in step S2 is between 10nm and 20nm; the thickness of the GaN buffer layer produced in step S2 is between 10nm and 20nm; the thickness of the GaN channel layer produced in step S2 is between 200nm and 300nm; the thickness of the AlN spacer layer produced in step S2 is between 1nm and 1.5nm; the thickness of the AlGaN barrier layer produced in step S2 is between 20nm and 25nm; the thickness of the GaN cap layer produced in step S2 is between 2nm and 5nm.

7. The method for growing an epitaxial wafer based on a sapphire substrate according to claim 5, characterized in that: The Al composition of the AlGaN barrier layer produced in step S2 is between 15% and 25%.

8. The method for growing an epitaxial wafer based on a sapphire substrate according to claim 5, characterized in that: The size of the sapphire substrate in step S1 is 2 inches, 4 inches, 6 inches or 8 inches.

9. The method for growing an epitaxial wafer based on a sapphire substrate according to claim 5, characterized in that: The process of making the AlN thin film layer in step S1 is as follows: The AlN thin film layer is formed on the sapphire substrate by a PVD sputtering method, and the temperature of the formation is set between 500 degrees Celsius and 550 degrees Celsius.

10. A method for growing an epitaxial wafer based on a sapphire substrate according to any one of claims 5 to 9, characterized in that: The process of making the AlN growth layer in step S2 is as follows: In the MOCVD reactor, the temperature is first raised to 1050 degrees Celsius to perform high-temperature treatment on the sapphire substrate for 2 minutes, and H2 is introduced, wherein the flow rate of H2 is between 120L and 180L; Then, before the growth, 5-10S of trimethylaluminum is introduced into the MOCVD reactor, wherein the flow rate of trimethylaluminum is 50-100 sccm; Then, H2, NH3 and trimethylaluminum are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of NH3 is between 1 and 2 L, the flow rate of trimethylaluminum is between 100 and 200 sccm, and the temperature is set between 1000 and 1050 degrees Celsius; The process of making the AlGaN buffer layer in step S2 is as follows: The temperature of the MOCVD reactor is set between 900 and 950 degrees Celsius, and H2, NH3, trimethylaluminum and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of NH3 is between 5 and 10 L, the flow rate of trimethylaluminum is between 200 and 400 sccm, and the flow rate of trimethylgallium is between 20 and 100 sccm; The process of making the GaN buffer layer in step S2 is as follows: N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 5 and 20 L, and the flow rate of trimethylgallium is between 200 and 400 sccm; The process of making the GaN channel layer in step S2 is as follows: The temperature of the MOCVD reactor is set between 1000 and 1050 degrees Celsius, and N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 20 and 50 L, and the flow rate of trimethylgallium is between 200 and 400 sccm; The process of making the AlN spacer layer in step S2 is as follows: The temperature of the MOCVD reactor is set between 1050 and 1100 degrees Celsius, and H2 and trimethylaluminum are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, and the flow rate of trimethylaluminum is between 100 and 200 sccm; The process of making the AlGaN barrier layer in step S2 is as follows: The temperature of the MOCVD reactor is set between 1000 and 1050 degrees Celsius, and H2, trimethylaluminum and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of H2 is between 120 and 180 L, the flow rate of trimethylaluminum is between 300 and 500 sccm, and the flow rate of trimethylgallium is between 100 and 200 sccm; The process of making the GaN cap layer in step S2 is as follows: The temperature of the MOCVD reactor is set between 1050 and 1100 degrees Celsius, and N2, H2, NH3 and trimethylgallium are introduced into the MOCVD reactor, wherein the flow rate of N2 is between 60 and 100 L, the flow rate of H2 is between 50 and 120 L, the flow rate of NH3 is between 20 and 50 L, and the flow rate of trimethylgallium is between 200 and 400 sccm.

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