A method of bonding diamond to gallium nitride

Abstract

This invention discloses a method for bonding diamond to gallium nitride (GaN), comprising preparing single-crystal diamond and a GaN epitaxial wafer, etching the GaN epitaxial wafer to form a layered stepped structure, then bombarding the GaN surface with an Ar ion beam to activate it, depositing an intermediate layer on the surface, thinning the intermediate layer to expose the central GaN portion after deposition, polishing after thinning, immersing the GaN and single-crystal diamond in acidic and alkaline solutions respectively, then bonding them by applying pressure and high-temperature annealing, and finally removing the substrate of the GaN epitaxial wafer to obtain GaN / diamond. This invention, through its layered stepped structure design, not only achieves bonding between diamond and GaN but also effectively reduces interfacial thermal resistance, significantly increases the contact area, enables more uniform and sufficient heat dissipation in GaN devices, and solves the problem of differences in thermal expansion coefficients.

Description

Technical Field

[0001] This invention relates to a method for integrating gallium nitride and diamond based on low interfacial thermal resistance, belonging to the field of semiconductor technology. Background Technology

[0002] Currently, with the rapid development of modern electronic devices towards high frequency, high power and high integration, more stringent requirements have been placed on the thermal management capabilities of semiconductor materials, especially in the fields of high-power electronic devices and high-frequency microwave devices.

[0003] Gallium nitride (GaN) exhibits remarkable application potential due to its unique physical properties, such as wide bandgap, high intrinsic breakdown electric field, and high electron saturation velocity. While GaN-based power devices theoretically possess high power density, in practical applications, their power density often only reaches a quarter of the theoretical value due to severe self-heating effects in high-power modes. This is primarily because the heat generated by GaN-based power devices accumulates rapidly during high-power operation and is difficult to dissipate effectively.

[0004] Generally, GaN power devices are typically fabricated on silicon and silicon carbide substrates. However, these raw substrates have relatively low thermal conductivity, which fails to meet heat dissipation requirements, leading to severe performance degradation and significantly limiting the application range of GaN power devices. Therefore, improving the thermal management level of GaN devices has become crucial for further enhancing their performance.

[0005] Diamond, a material with ultra-high thermal conductivity, extremely low coefficient of thermal expansion, high resistivity, and excellent chemical inertness, is considered an ideal substrate material for high-power electronic devices. Integrating diamond with GaN can effectively improve the heat dissipation capacity of the near-junction region of GaN devices, reduce peak temperature, and thus significantly improve device reliability and performance.

[0006] In existing technologies, the integration methods of diamond and GaN are mainly divided into three categories: growing GaN on diamond, growing diamond on GaN, and bonding diamond and GaN. The first two methods are limited in practical production due to lattice mismatch and differences in thermal expansion coefficients between the materials, as well as wafer warping and cracking caused by high-temperature processes. Therefore, bonding technology between diamond and GaN is a good solution.

[0007] Existing technologies for bonding diamond and GaN include: 1) A bonding method disclosed in CN111599693A, which uses an embedded structure of protrusions and grooves for bonding. By extruding and embedding copper nano-paste in the grooves, the thickness of the solder paste can be well controlled, resulting in a more uniform solder paste, which helps to reduce bonding defects and improve product strength; 2) A gallium nitride semiconductor structure and its fabrication method disclosed in CN113299736A, which forms a gallium nitride layer on a composite patterned substrate. During the growth process, the dislocation density can be further reduced and the dislocations can be concentrated in a specific region to form a defect closure region. The gallium nitride material formed in other growth regions has almost no dislocation defects. Then, trenches and insulating barrier layers are formed on the defect closure region. The insulating barrier layer can prevent electrode metal and impurity metal elements from diffusing into the dislocations, thus preventing the formation of leakage channels. Moreover, there are no dislocations in the gallium nitride layer under the ohmic contact region or Schottky contact region, thereby improving the reliability and stability of the device.

[0008] However, in diamond-GaN bonding technology, using intermediate layers such as Si, SiO2, and SiC can avoid lattice mismatch and differences in thermal expansion coefficients caused by high-temperature growth, but it increases interfacial thermal resistance. While metal diffusion techniques such as Au, Ag, Mo, and Cu can increase bonding strength, they also affect thermal conductivity and introduce differences in thermal expansion coefficients. Direct bonding between diamond and GaN does not decrease thermal conductivity, but it suffers from insufficient bonding strength and thermal expansion coefficient mismatch. Traditional bonding structures typically employ planar contact designs with limited contact area, resulting in high interfacial thermal resistance. Heat easily accumulates at the interface, affecting the device's heat dissipation performance. Furthermore, the lack of stress relief mechanisms makes it prone to stress concentration due to the difference in thermal expansion coefficients between GaN and diamond under high-temperature operating conditions, leading to interfacial cracks or delamination, severely impacting device reliability. Traditional single-layer bonding structures have a single heat conduction path and low heat conduction efficiency at the interface, making the device prone to localized overheating during high-power operation. Summary of the Invention

[0009] The purpose of this invention is to provide a method for bonding diamond and gallium nitride to solve at least one of the above-mentioned technical problems, thereby overcoming the limitations of existing technologies and providing a new approach to improve the performance of GaN-based power devices. This method not only enables the bonding of diamond and GaN but also effectively reduces interfacial thermal resistance, solves the problem of thermal expansion coefficient mismatch, and enables more uniform and sufficient heat dissipation of GaN devices, thus improving mechanical stability. This has significant scientific and application value for promoting the development of diamond-based GaN power devices.

[0010] This invention achieves the above objective through the following technical solution: a method for bonding diamond to gallium nitride, the method comprising the following steps:

[0011] S1. Prepare single-crystal diamond and GaN grown on sapphire or Si substrate, wherein the Ra of single-crystal diamond is less than 10 nm and the Ra of GaN is less than 5 nm.

[0012] S2. Use a mask with a layered stepped structure to etch the GaN epitaxial wafer to form a layered stepped structure. After etching, perform ultrasonic cleaning and nitrogen drying on the GaN and single crystal diamond.

[0013] S3. The GaN surface is bombarded with an Ar ion beam to remove the oxide layer and activate the GaN surface. Then, a buffer layer is grown on the GaN surface, and the buffer layer fills both sides of the step and covers the middle GaN.

[0014] S4. Thin the grown buffer layer to expose the middle region of GaN and polish it;

[0015] S5. Immerse the thinned and polished GaN epitaxial wafer and single crystal diamond in different solutions respectively.

[0016] S6. The soaked GaN epitaxial wafer and single crystal diamond are washed with deionized water and dried with nitrogen to obtain GaN epitaxial wafer samples and single crystal diamond samples. The GaN epitaxial wafer samples and single crystal diamond samples are brought into contact with each other and pressure is applied during high-temperature annealing to bond them together. After completion, the substrate on the GaN epitaxial wafer is removed to obtain the target GaN / diamond.

[0017] As a further aspect of the present invention: in S2, the GaN epitaxial wafer is etched into a three-layer stepped structure, and the method of etching into a three-layer stepped structure includes, but is not limited to, chemical etching, plasma etching and electron beam etching.

[0018] As a further aspect of the present invention: in S2, the method for etching the GaN epitaxial wafer into a three-layer stepped structure includes:

[0019] 1) The first layer is etched to a depth of 50-70nm, forming a wide convex structure at the bottom layer;

[0020] 2) The second layer is etched to a depth of 25-40nm, forming a convex structure in the intermediate layer;

[0021] 3) The third layer is etched to a depth of 50-120nm, forming the topmost convex structure.

[0022] As a further embodiment of the present invention: In S2, the ultrasonic cleaning method uses acetone, ethyl ketone, and deionized water to perform ultrasonic cleaning for 5-10 minutes in sequence.

[0023] As a further embodiment of the present invention: in S3, the buffer layer grown on the GaN surface is a SiC or AlN intermediate layer.

[0024] As a further aspect of the present invention: in S3, the method for growing a buffer layer on the GaN surface includes, but is not limited to, plasma-enhanced chemical vapor deposition and magnetron sputtering.

[0025] As a further aspect of the present invention: In S3, the method for growing a buffer layer on the GaN surface specifically includes:

[0026] 1) The buffer layer fills both sides of the bottom convex structure to form the first layer structure;

[0027] 2) The buffer layer fills both sides of the convex structure of the intermediate layer to form a second layer structure;

[0028] 3) The buffer layer fills both sides of the topmost convex structure to form a third layer structure and completely covers GaN.

[0029] As a further embodiment of the present invention: in S5, the GaN epitaxial wafer is soaked in an acid solution, and the sapphire or Si substrate is soaked in an alkaline solution. The acid solution includes, but is not limited to, dilute hydrochloric acid and dilute sulfuric acid, and the alkaline solution includes, but is not limited to, a mixture of NaOH, NH4OH and H2O2.

[0030] As a further embodiment of the present invention: in S6, the high-temperature annealing temperature is 200-350°C, the applied pressure is 1-2 MPa, and the time is 2-3 hours.

[0031] As a further aspect of the present invention: in S6, the method for removing the substrate on the GaN epitaxial wafer includes, but is not limited to, mechanical separation and laser separation.

[0032] The beneficial effects of this invention are:

[0033] 1) The present invention significantly increases the contact area between GaN and diamond and the intermediate layer through the convex design of the multi-layer (three-layer) stepped structure, thereby reducing the interface thermal resistance and effectively improving the heat conduction efficiency. Furthermore, through the multi-layer stress dispersion mechanism, it alleviates the stress concentration problem caused by the difference in thermal expansion coefficient, thereby reducing the probability of interface crack formation, enhancing the mechanical stability of the bonding interface, and improving the reliability and heat dissipation of the device.

[0034] 2) Through the structural design and process optimization of this invention, the performance integrity of the gallium nitride and diamond bonding can be maintained. This not only effectively solves the problems of high interface thermal resistance, low bonding strength and difference in thermal expansion coefficient in the prior art, but also realizes the uniformity and sufficiency of heat dissipation of GaN devices, improves mechanical stability, and provides a new technical approach for high-performance heat dissipation of GaN-based power devices. It has important scientific significance and broad application prospects. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of GaN grown on the substrate of the present invention;

[0036] Figure 2 This is a schematic diagram of the three-layer stepped GaN epitaxial wafer obtained after etching according to the present invention;

[0037] Figure 3 This is a schematic diagram of the intermediate layer grown on the layered stepped GaN epitaxial wafer of the present invention;

[0038] Figure 4 This is a schematic diagram showing the intermediate layer of the present invention after it has been thinned to expose the intermediate region of GaN;

[0039] Figure 5 This is a schematic diagram of GaN and diamond after soaking and bonding according to the present invention;

[0040] Figure 6 This is a schematic diagram of the target GaN / diamond obtained after removing the substrate according to the present invention;

[0041] In the diagram: 1. Sapphire or Si substrate, 2. GaN, 3. SiC or AlN interlayer, 4. Single crystal diamond. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1: This example provides a method for bonding diamond to gallium nitride, the method comprising the following steps:

[0044] First: such as Figure 1 As shown, a single-crystal diamond 4 and a GaN2 grown on a sapphire or Si substrate 1 are prepared, wherein the Ra of the single-crystal diamond 4 is less than 10 nm and the Ra of the GaN2 is less than 5 nm.

[0045] Second: Use a layered stepped structure mask to etch the GaN epitaxial wafer to form a layered stepped structure. After etching, ultrasonically clean the GaN2 and single crystal diamond 4, and then dry them with nitrogen.

[0046] like Figure 2 As shown, the GaN epitaxial wafer is etched into a three-layer stepped structure, and the methods for etching into the three-layer stepped structure include, but are not limited to, chemical etching, plasma etching, and electron beam etching.

[0047] Methods for etching GaN epitaxial wafers into a three-layer stepped structure include:

[0048] 1) The first layer is etched to a depth of 50-70nm, forming a wide convex structure at the bottom layer;

[0049] 2) The second layer is etched to a depth of 25-40nm, forming a convex structure in the intermediate layer;

[0050] 3) The third layer is etched to a depth of 50-120nm, forming the topmost convex structure.

[0051] The ultrasonic cleaning method involves sequentially using acetone, ethyl ketone, and deionized water for 5-10 minutes.

[0052] Third: The GaN2 surface is bombarded with an Ar ion beam to remove the oxide layer and activate the GaN2 surface. Then, a buffer layer is grown on the GaN2 surface, which fills both sides of the step and covers the middle GaN2.

[0053] like Figure 3 As shown, the buffer layer grown on the GaN2 surface is a SiC or AlN intermediate layer 3. Methods for growing the buffer layer on the GaN2 surface include, but are not limited to, plasma-enhanced chemical vapor deposition and magnetron sputtering.

[0054] The specific methods for growing a buffer layer on the GaN2 surface include:

[0055] 1) The buffer layer fills both sides of the bottom convex structure to form the first layer structure;

[0056] 2) The buffer layer fills both sides of the convex structure of the intermediate layer to form a second layer structure;

[0057] 3) The buffer layer fills both sides of the topmost convex structure to form a third layer structure and completely covers GaN2.

[0058] Fourth: such as Figure 4 As shown, the grown buffer layer is thinned to expose the middle region of GaN2 and then polished.

[0059] Fifth: Immerse the thinned and polished GaN epitaxial wafer and single-crystal diamond 4 in different solutions respectively.

[0060] The GaN epitaxial wafer is immersed in a prepared acid solution, and the sapphire or Si substrate 1 is immersed in a prepared alkaline solution. The acid solution includes, but is not limited to, dilute hydrochloric acid and dilute sulfuric acid, and the alkaline solution includes, but is not limited to, a mixture of NaOH, NH4OH and H2O2.

[0061] Sixth: such as Figure 5 As shown, the soaked GaN epitaxial wafer and single-crystal diamond 4 were washed with deionized water and dried with nitrogen to obtain GaN epitaxial wafer samples and single-crystal diamond 4 samples. The GaN epitaxial wafer samples and single-crystal diamond 4 samples were brought into contact and bonded together under pressure while undergoing high-temperature annealing. After completion, the substrate on the GaN epitaxial wafer was removed to obtain the target GaN / diamond, as shown. Figure 6 As shown.

[0062] The high-temperature annealing temperature is 200-350℃, the pressure is 1-2MPa, and the time is 2-3h; the methods for removing the substrate from the GaN epitaxial wafer include, but are not limited to, mechanical separation and laser separation.

[0063] Example 2: This example provides a method for preparing GaN / diamond bonds, the specific preparation method is as follows:

[0064] The first step involves uniformly coating a layer of photoresist onto the sapphire-based GaN surface and performing a soft bake (80°C) for one minute to remove air bubbles. Using a pre-designed layered stepped mask, the mask is aligned with the GaN epitaxial wafer, and ultraviolet light exposure is performed (exposure energy 100 mJ / cm²). After exposure, a post-bake (110°C, 1 minute) is performed to cure the photoresist. Subsequently, development is carried out using a developer (such as KMPR developer) to remove the photoresist from unexposed areas, exposing the GaN surface. The GaN epitaxial wafer is then etched using an acidic mixed solution (HCl:H3PO4:H2O2 = 1:1:1 ratio) at the following etching temperature: The etching process, conducted at 30-80℃, consists of three steps, forming three stepped structures: the first layer has an etching depth of 60nm, forming a wide convex structure at the bottom; the second layer has an etching depth of 30nm, forming a convex structure in the middle layer; and the third layer has an etching depth of 15nm, forming a convex structure at the top. The width decreases from bottom to top. After reaching the required etching depth, the etching solution and photoresist residue are washed away with deionized water, and the remaining photoresist is removed with a photoresist remover (acetone). After completion, the sapphire-based GaN epitaxial wafer and single-crystal diamond are ultrasonically cleaned for 5-10 minutes in sequence with acetone, ethyl ketone, and deionized water.

[0065] The second step involves bombarding the sapphire-based GaN surface with an Ar ion beam to remove the surface oxide layer and activate the surface. The ion energy is 1-2 keV, and the ion flux is 10-100 μA / cm.2 The bombardment time is 1-3 minutes. After completion, SiC is deposited on GaN using plasma-enhanced chemical vapor deposition (PECVD). The cleaned sapphire-based GaN is placed in the PECVD reaction chamber, and after evacuating to the required working pressure, precursor gases for SiC deposition are introduced, including silicon sources (such as silane SiH4), carbon sources (such as methane CH4), and dilution gases (such as hydrogen H2). During deposition, the SiC intermediate layer first fills both sides of the bottommost wide convex structure, forming the first SiC-GaN-SiC structure; then it fills both sides of the intermediate layer's convex structure, forming the second SiC-GaN-SiC structure; finally, it fills both sides of the topmost convex structure, forming the third SiC-GaN-SiC structure and completely covering the GaN. Gas flow rates: SiH4: 20 sccm, CH4: 40 sccm, RF power: 150 W, deposition pressure: 50-80 Pa, deposition temperature: 500℃, deposition thickness: 120-150 nm.

[0066] The third step involves using laser thinning to thin the SiC intermediate layer of the deposited sapphire-based GaN to expose the GaN region in the middle of the top layer. After completion, a nanodiamond particle polishing slurry is selected for polishing.

[0067] The fourth step involves placing the SiC-deposited sapphire-based GaN into a prepared dilute sulfuric acid solution, and the single-crystal diamond into a prepared NaOH / H2O2 mixed solution. The concentration of the dilute sulfuric acid solution is 30%, and the NaOH / H2O2 mixture consists of 20 mL of 15% NaOH solution, 20 mL of 25% H2O2 solution, and 50 mL of deionized water. The soaking temperature is 60℃, and the soaking time is 10 min.

[0068] The fifth step involves cleaning the soaked GaN epitaxial wafer and single-crystal diamond with deionized water and drying them with nitrogen. Then, they are placed in an inert gas environment and subjected to pressure during high-temperature annealing to bond them together. Annealing temperature: 100℃, applied pressure: 1MPa, bonding time: 2h.

[0069] The sixth step involves mechanically separating the sapphire substrate and the GaN / diamond, removing the sapphire substrate, and obtaining the target GaN / diamond.

[0070] Example 3: This example provides a method for preparing GaN / diamond bonds, the method is as follows:

[0071] The first step involves uniformly coating a layer of photoresist onto the Si-based GaN surface and then performing a soft bake (90°C) for one minute to remove air bubbles. Using a pre-designed layered stepped mask, the mask is aligned with the GaN epitaxial wafer, and ultraviolet light exposure is performed (exposure energy of 120 mJ / cm²). After exposure, a post-bake (100°C, 1 min) is performed to cure the photoresist. Then, development is carried out with a developer (such as sodium carbonate solution or KMPR solution) to remove the photoresist from unexposed areas, exposing the GaN surface. The surface is then placed in a plasma etching machine and etched using a mixed gas of Cl₂ and Ar. The Cl₂ flow rate is 50-100 sccm, the Ar flow rate is 20-50 sccm, the RF power is 300-500 W, and the etching temperature is 15°C. At 0℃, the etching process consists of three steps, forming three stepped structures: the first layer has an etching depth of 50nm, forming the bottom layer with a wide convex structure; the second layer has an etching depth of 25nm, forming the middle layer with a convex structure; and the third layer has an etching depth of 15nm, forming the top layer with a convex structure. The width decreases from bottom to top. After reaching the required etching depth, the photoresist residue is washed away with deionized water, and then the remaining photoresist is removed with a photoresist remover (N-methylpyrrolidone). After completion, the sapphire-based GaN epitaxial wafer and single crystal diamond are ultrasonically cleaned with acetone, ethyl ketone, and deionized water for 5-10 minutes in sequence.

[0072] The second step involves bombarding the Si-based GaN surface with an Ar ion beam to remove the surface oxide layer and activate the surface. Ion energy: 2-3 keV, ion flux: 20-80 μA / cm². 2 The bombardment time is 1-3 minutes. After completion, AlN is deposited on GaN using magnetron sputtering. The cleaned Si-based GaN is placed in the vacuum chamber of the magnetron sputtering system, and after evacuating to the required working pressure, the AlN sputtering target material is loaded. The sputtering power supply is started to generate a magnetic field and ions, causing argon (Ar) ions to bombard the AlN target material, sputtering AlN atoms or molecules from the target surface and depositing them on the GaN substrate. During the deposition process, the intermediate AlN layer first fills both sides of the bottommost wide convex structure, forming the first AlN-GaN-AlN structure; then it fills both sides of the intermediate convex structure, forming the second AlN-GaN-AlN structure; finally, it fills both sides of the topmost convex structure, forming the third AlN-GaN-AlN structure and completely covering the GaN. Ar flow rate: 50-80 sccm, sputtering power: 300-500 W, sputtering pressure: 2-5 Pa, sputtering temperature: 400-450℃, sputtering thickness: 90-120 nm.

[0073] The third step involves using laser thinning to thin the AlN intermediate layer of the deposited sapphire-based GaN until the GaN region in the middle of the top layer is exposed. After completion, an alkaline solution containing Al2O3 particles is selected for polishing.

[0074] In the fourth step, the Si-based GaN with deposited AlN was placed in a prepared dilute hydrochloric acid solution, and the single-crystal diamond was placed in a prepared mixed solution of NH4OH / H2O2. The concentration of the dilute hydrochloric acid solution was 20%, and the NH4OH / H2O2 mixture consisted of 15 mL of 25% NH4OH solution, 15 mL of 25% H2O2 solution, and 30 mL of deionized water. The immersion temperature was 60℃, and the time was 10 min.

[0075] The fifth step involves washing the soaked Si-based GaN and single-crystal diamond with deionized water and drying them with nitrogen. Then, the mixture is placed in an inert gas environment and subjected to pressure during high-temperature annealing to bond the materials together. Annealing temperature: 350℃, pressure: 2MPa, bonding time: 3h.

[0076] The sixth step involves laser separation of the Si substrate and GaN / diamond to remove the Si substrate and obtain the target GaN / diamond.

[0077] Working process: First, prepare single-crystal diamond and GaN epitaxial wafers, and etch the GaN epitaxial wafer to form a layered stepped structure; second, bombard the GaN surface with an Ar ion beam to activate it, deposit an intermediate layer on the surface, and after deposition, thin the intermediate layer to expose the middle GaN part, and then polish it; then, immerse GaN and single-crystal diamond in acidic and alkaline solutions respectively, and after completion, apply pressure to them and anneal them at high temperature to bond them; finally, remove the substrate of the GaN epitaxial wafer to obtain the desired interface thermal resistance GaN / diamond.

[0078] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0079] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for bonding diamond to gallium nitride, characterized in that, The method includes the following steps: S1. Prepare single-crystal diamond (4) and GaN (2) grown on sapphire or Si substrate (1), wherein the Ra of single-crystal diamond (4) is less than 10 nm and the Ra of GaN (2) is less than 5 nm. S2. Use a mask with a layered stepped structure to etch the GaN epitaxial wafer to form a layered stepped structure. After etching, ultrasonic cleaning and nitrogen drying are performed on GaN (2) and single crystal diamond (4). In step S2, the GaN epitaxial wafer is etched into a three-layer stepped structure, and the method for etching into the three-layer stepped structure includes, but is not limited to, chemical etching, plasma etching, and electron beam etching. In step S2, the method for etching the GaN epitaxial wafer into a three-layer stepped structure includes: 1) The first layer is etched to a depth of 50-70nm, forming a wide convex structure at the bottom layer; 2) The second layer is etched to a depth of 25-40nm, forming a convex structure in the intermediate layer; 3) The third layer is etched to a depth of 50-120nm, forming the convex structure of the uppermost layer; S3. The GaN(2) surface is bombarded with an Ar ion beam to remove the oxide layer and activate the GaN(2) surface. Then, a buffer layer is grown on the GaN(2) surface, while the buffer layer fills both sides of the step and covers the middle GaN(2). In S3, the buffer layer grown on the GaN (2) surface is a SiC or AlN intermediate layer (3); In S3, the method for growing a buffer layer on the GaN(2) surface specifically includes: 1) The buffer layer fills both sides of the bottom convex structure to form the first layer structure; 2) The buffer layer fills both sides of the convex structure of the intermediate layer to form a second layer structure; 3) The buffer layer fills both sides of the uppermost convex structure, forming a third layer structure and completely covering GaN(2); S4. Thin the grown buffer layer to expose the middle region of GaN(2) and polish it; S5. The thinned and polished GaN epitaxial wafer and single crystal diamond (4) are immersed in different solutions respectively; S6. The soaked GaN epitaxial wafer and single crystal diamond (4) are washed with deionized water and dried with nitrogen to obtain GaN epitaxial wafer sample and single crystal diamond (4) sample. The GaN epitaxial wafer sample and single crystal diamond (4) sample are brought into contact with each other and pressure is applied during high-temperature annealing to bond them together. After completion, the substrate on the GaN epitaxial wafer is removed to obtain the target GaN / diamond.

2. The method according to claim 1, characterized in that: In step S2, the ultrasonic cleaning method uses acetone, ethyl ketone, and deionized water to perform ultrasonic cleaning for 5-10 minutes in sequence.

3. The method according to claim 1, characterized in that: In S3, the method for growing a buffer layer on the GaN (2) surface includes, but is not limited to, plasma-enhanced chemical vapor deposition and magnetron sputtering.

4. The method according to claim 1, characterized in that: In S5, the GaN epitaxial wafer is soaked in an acid solution, and the sapphire or Si substrate (1) is soaked in an alkaline solution. The acid solution includes, but is not limited to, dilute hydrochloric acid and dilute sulfuric acid, and the alkaline solution includes, but is not limited to, a mixture of NaOH, NH4OH and H2O2.

5. The method according to claim 1, characterized in that: In step S6, the high-temperature annealing temperature is 200-350℃, the applied pressure is 1-2MPa, and the time is 2-3h.

6. The method according to claim 1, characterized in that: In step S6, the methods for removing the substrate from the GaN epitaxial wafer include, but are not limited to, mechanical separation and laser separation.

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