Diamond and gallium nitride bonding method

Abstract

The invention discloses a method for bonding diamond and gallium nitride, which comprises the following steps of: preparing monocrystal diamond and a GaN epitaxial wafer, etching the GaN epitaxial wafer to form a layered stepped structure, bombarding GaN by using Ar ion beams to activate the surface of the GaN, depositing an intermediate layer on the surface, thinning the intermediate layer until the middle GaN part is exposed after the deposition is completed, polishing after the thinning is completed, and finally, carrying out the bonding of the diamond and the gallium nitride. The method comprises the following steps: respectively soaking GaN and monocrystal diamond in an acidic solution and an alkaline solution, enabling the GaN and the monocrystal diamond to be in contact with each other after soaking, applying pressure, performing high-temperature annealing for bonding, and then removing a substrate of a GaN epitaxial wafer to finally obtain the GaN / diamond. Through the layered stepped structural design, the bonding of diamond and GaN can be realized, the interface thermal resistance can be effectively reduced, the contact area is obviously increased, the heat dissipation of a GaN device can be more uniform and sufficient, and the problem of difference of thermal expansion coefficients is solved.

Description

Technical Field

[0001] The present invention relates to an integration method of gallium nitride and diamond based on low interfacial thermal resistance, belonging to the field of semiconductor technology. Background Art

[0002] Currently, with the rapid development of modern electronic devices towards high frequency, high power and high integration, more stringent requirements are imposed 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 excellent application potential due to its unique physical properties, such as wide bandgap, high intrinsic breakdown electric field and high electron saturation velocity. The theoretical power density of GaN-based power devices is very high. However, in practical applications, due to the severe self-heating effect of the devices in the high-power mode, their power density can often only reach one-fourth of the theory, which is mainly because the heat generated by GaN-based power devices during high-power operation accumulates rapidly and is difficult to dissipate effectively.

[0004] Generally speaking, GaN power devices are usually fabricated on silicon and silicon carbide substrates. However, the thermal conductivities of these original substrates are relatively low and cannot meet the heat dissipation requirements, resulting in serious degradation of device performance and greatly limiting the application scope of GaN power devices. Therefore, how to improve the thermal management level of GaN devices has become the key to further enhancing their performance.

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

[0006] In the prior art, 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 their practical production applications due to lattice mismatch and differences in thermal expansion coefficients between materials, as well as problems such as wafer warping and cracking caused by high-temperature processes. Therefore, the bonding technology of diamond and GaN is a good solution.

[0007] The bonding technologies for diamond and GaN in the prior art include: 1) a bonding method disclosed in publication number CN111599693A, which is bonded through an embedded structure of protrusions and grooves, and by squeezing and embedding the copper nanopaste in the groove, the thickness of the solder paste can be well controlled to form a more uniform solder paste, which is beneficial to reduce bonding defects and help improve product strength; 2) a gallium nitride semiconductor structure and a preparation method disclosed in publication number CN113299736A, which forms a gallium nitride layer on a composite pattern substrate, and can further reduce the dislocation density during the growth process and can concentrate the dislocations in a specific area to form a defect closure area, while the gallium nitride material formed in other growth areas has almost no dislocation defects, and then a groove and an insulating barrier layer are formed on the defect closure area, wherein the insulating barrier layer can prevent the electrode metal and impurity metal elements from diffusing into the dislocation, thereby preventing the formation of a leakage channel, and the gallium nitride layer below the ohmic contact area or the Schottky contact area has no dislocations, thereby improving the reliability and stability of the device.

[0008] However, in the bonding technology of diamond and GaN, Si, SiO 2 Intermediate layers such as SiC can avoid lattice mismatch and difference in thermal expansion coefficient caused by high-temperature growth, but will increase interface thermal resistance; using metal diffusion technology such as Au, Ag, Mo, Cu, etc., although it can increase bonding strength, it will also affect thermal conductivity and bring about the problem of difference in thermal expansion coefficient; direct bonding of diamond and GaN will not reduce thermal conductivity, but there are problems of insufficient bonding strength and mismatch in thermal expansion coefficient. Traditional bonding structures usually adopt a planar contact design with limited contact area, resulting in high interface thermal resistance, heat is easily accumulated at the interface, affecting the heat dissipation performance of the device, and lacks a stress release mechanism. In a high-temperature working environment, stress concentration is easily generated due to the difference in thermal expansion coefficient between GaN and diamond, resulting in interface cracks or peeling, which seriously affects the reliability of the device; the traditional ordinary single-layer bonding structure has a single thermal conduction path, and the heat conduction efficiency at the interface is low, which makes the device prone to local overheating when running at high power. Summary of the invention

[0009] The purpose of the present invention is to provide a method for bonding diamond to gallium nitride in order to solve at least one of the above technical problems, so as to overcome the limitations of the prior art and provide a new way to improve the performance of GaN-based power devices. It can not only achieve the bonding of diamond to GaN, but also effectively reduce the interface thermal resistance, solve the problem of thermal expansion coefficient mismatch, and make the heat dissipation of GaN devices more uniform and sufficient, and improve mechanical stability. It has important scientific significance and application value for promoting the development of diamond-based GaN power devices.

[0010] The present invention achieves the above object through the following technical solutions: A method for bonding diamond and gallium nitride, the method comprising the following steps: S1. Prepare single-crystal diamond and GaN grown on a sapphire or Si substrate. Among them, the Ra of the single-crystal diamond is less than 10 nm, and the Ra of the GaN 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 the etching is completed, ultrasonically clean the GaN and the single-crystal diamond and dry them with nitrogen; S3. Bombard the surface of the GaN with an Ar ion beam to remove the oxide layer and activate the surface of the GaN, and then grow a buffer layer on the surface of the GaN. At the same time, the buffer layer fills both sides of the step and covers the middle GaN; S4. Thin the grown buffer layer until the middle region of the GaN is exposed and polish it; S5. Immerse the thinned and polished GaN epitaxial wafer and the single-crystal diamond in different solutions respectively; S6. Clean the immersed GaN epitaxial wafer and the single-crystal diamond with deionized water and dry them with nitrogen to obtain a sample of the GaN epitaxial wafer and a sample of the single-crystal diamond. Contact the sample of the GaN epitaxial wafer and the sample of the single-crystal diamond with each other, apply pressure while performing high-temperature annealing to bond them, and after completion, remove the substrate on the GaN epitaxial wafer to obtain the target GaN / diamond.

[0011] As a further scheme of the present invention: In S2, the GaN epitaxial wafer is etched into a three-layer stepped structure, and the method for etching into a three-layer stepped structure includes but is not limited to chemical etching, plasma etching, and electron beam etching.

[0012] As a further scheme of the present invention: In S2, the method for etching the GaN epitaxial wafer into a three-layer stepped structure includes: 1) The etching depth of the first layer is 50 - 70 nm to form a wide convex structure at the bottom layer; 2) The etching depth of the second layer is 25 - 40 nm to form a convex structure in the middle layer; 3) The etching depth of the third layer is 50 - 120 nm to form a convex structure at the top layer.

[0013] As a further scheme of the present invention: In S2, the ultrasonic cleaning method uses acetone, acetone, and deionized water to perform ultrasonic cleaning in sequence for 5 - 10 min.

[0014] As a further scheme of the present invention: In S3, the buffer layer grown on the GaN surface is an SiC or AlN intermediate layer.

[0015] As a further aspect of the present invention: In S3, the method for growing a buffer layer on the surface of GaN includes, but is not limited to, plasma-enhanced chemical vapor deposition and magnetron sputtering.

[0016] As a further aspect of the present invention: In S3, the method for growing a buffer layer on the surface of GaN specifically includes: 1) The buffer layer fills both sides of the bottommost convex structure to form a first layer structure; 2) The buffer layer fills both sides of the middle convex structure to form a second layer structure; 3) The buffer layer fills both sides of the uppermost convex structure to form a third layer structure and completely covers the GaN.

[0017] As a further aspect 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, NaOH, NH 4 OH and H 2 O 2 mixed.

[0018] As a further aspect of the present invention: In S6, the temperature of the high-temperature annealing is 200 - 350 °C, the applied pressure is 1 - 2 MPa, and the time is 2 - 3 h.

[0019] 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.

[0020] The beneficial effects of the present invention are: 1) Through the convex design of the multi-layer (three-layer) stepped structure in the present invention, the contact area between GaN and diamond and the intermediate layer is significantly increased, reducing the interface thermal resistance, effectively improving the heat conduction efficiency, and through the multi-level stress dispersion mechanism, the stress concentration problem caused by the difference in thermal expansion coefficients is alleviated, reducing the generation probability of interface cracks, enhancing the mechanical stability of the bonding interface, and improving the reliability and heat dissipation of the device; 2) Through the structural design and process optimization of the present invention, the performance integrity of the bonding between gallium nitride and diamond can be maintained. It not only effectively solves the problems of high interface thermal resistance, low bonding strength, and difference in thermal expansion coefficients existing in the prior art, but also realizes the uniformity and sufficiency of heat dissipation of GaN devices, improves the mechanical stability, provides a new technical idea for the high-performance heat dissipation of GaN-based power devices, and has important scientific significance and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of GaN grown on the substrate of the present invention; Figure 2 Schematic diagram of the three-layer stepped GaN epitaxial wafer obtained after etching according to the present invention; Figure 3 Schematic diagram after growing an intermediate layer on the layered stepped GaN epitaxial wafer according to the present invention; Figure 4 Schematic diagram after thinning the intermediate layer until the intermediate region of GaN is exposed according to the present invention; Figure 5 Schematic diagram after soaking and bonding GaN and diamond according to the present invention; Figure 6 Schematic diagram of the target GaN / diamond obtained after removing the substrate according to the present invention; In the figure: 1, sapphire or Si substrate, 2, GaN, 3, SiC or AlN intermediate layer, 4, single-crystal diamond. Detailed implementation manners

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] Embodiment 1, this embodiment provides a method for bonding diamond and gallium nitride, and this method includes the following steps: First: As Figure 1 shown, 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.

[0024] Second: Use a layered stepped structure mask to etch the GaN epitaxial wafer to form a layered stepped structure, and after the etching is completed, ultrasonically clean GaN 2 and single-crystal diamond 4, and then dry with nitrogen.

[0025] As Figure 2 shown, the GaN epitaxial wafer is etched into a three-layer stepped structure, and the method for etching it into a three-layer stepped structure includes but is not limited to chemical etching, plasma etching, and electron beam etching.

[0026] The method for etching the GaN epitaxial wafer into a three-layer stepped structure includes: 1) The etching depth of the first layer is 50 - 70 nm to form a wide convex structure at the bottom layer; 2) The etching depth of the second layer is 25 - 40 nm to form a convex structure in the intermediate layer; 3) The etching depth of the third layer is 50 - 120 nm to form a convex structure at the top layer.

[0027] The ultrasonic cleaning method uses acetone, methyl ethyl ketone, and deionized water to perform ultrasonic cleaning for 5 - 10 minutes in sequence.

[0028] Third: Bombard the surface of GaN2 with an Ar ion beam to remove the oxide layer and activate the surface of GaN2, and then grow a buffer layer on the surface of GaN2. At the same time, the buffer layer fills both sides of the step and covers the middle GaN2.

[0029] As Figure 3 shown, the buffer layer grown on the surface of GaN2 is the SiC or AlN intermediate layer 3. The methods for growing the buffer layer on the surface of GaN2 include, but are not limited to, plasma-enhanced chemical vapor deposition method and magnetron sputtering method.

[0030] The methods for growing the buffer layer on the surface of GaN2 specifically include: 1) The buffer layer fills both sides of the convex structure at the bottom layer to form the first layer structure; 2) The buffer layer fills both sides of the convex structure at the intermediate layer to form the second layer structure; 3) The buffer layer fills both sides of the convex structure at the top layer to form the third layer structure and cover all of GaN2.

[0031] Fourth: As Figure 4 shown, thin the grown buffer layer until the middle region of GaN2 is exposed and polish it.

[0032] Fifth: Immerse the thinned and polished GaN epitaxial wafer and single-crystal diamond 4 in different solutions respectively.

[0033] The GaN epitaxial wafer is immersed in the prepared acid solution, and the sapphire or Si substrate 1 is immersed in the prepared alkali solution. The acid solution includes, but is not limited to, dilute hydrochloric acid and dilute sulfuric acid, and the alkali solution includes, but is not limited to, NaOH, NH 4 OH and H 2 O 2 mixed.

[0034] Sixth: As Figure 5 shown, wash the immersed GaN epitaxial wafer and single-crystal diamond 4 with deionized water and dry them with nitrogen to obtain the samples of the GaN epitaxial wafer and the single-crystal diamond 4. Contact the samples of the GaN epitaxial wafer and the single-crystal diamond 4 with each other and apply pressure while performing high-temperature annealing to bond them. After completion, remove the substrate on the GaN epitaxial wafer to obtain the target GaN / diamond, as Figure 6 shown.

[0035] Among them, the temperature of high-temperature annealing is 200 - 350 °C, the applied pressure is 1 - 2 MPa, and the time is 2 - 3 h; the methods for removing the substrate on the GaN epitaxial wafer include but are not limited to mechanical separation and laser separation.

[0036] Example 2. This example provides a preparation method for GaN / diamond bonding. The specific preparation method is as follows: The first step is to uniformly coat a layer of photoresist on the surface of sapphire-based GaN, and perform soft baking (80 °C) for one minute to remove air bubbles. Using a pre-designed layered stepped structure mask, align the mask with the GaN epitaxial wafer, perform ultraviolet light exposure (exposure energy is 100 mJ / cm²), and perform post-baking (110 °C, 1 minute) after exposure to cure the photoresist. Subsequently, use a developer (such as KMPR developer) for development to remove the photoresist in the unexposed area, expose the GaN surface, and then use an acidic mixed solution (HCl:H 3 PO 4 :H 2 O 2 =1:1:1 ratio) to etch the GaN epitaxial wafer. The etching temperature is 30 - 80 °C. The etching process is divided into three steps to form three layers of stepped structures: the etching depth of the first layer is 60 nm to form a wide convex structure at the bottom layer; the etching depth of the second layer is 30 nm to form a convex structure in the middle layer; the etching depth of the third layer is 15 nm to form a convex structure at the top layer, and the width decreases from bottom to top. After reaching the required etching depth, use deionized water to wash away the etching solution and photoresist residues, and then use a photoresist remover (acetone) to remove the remaining photoresist. After completion, use acetone, methyl ethyl ketone, and deionized water to ultrasonically clean the sapphire-based GaN epitaxial wafer and single-crystal diamond for 5 - 10 min.

[0037] The second step is to bombard the surface of sapphire-based GaN with an Ar ion beam to remove the surface oxide layer and activate the surface. The ion energy is 1 - 2 keV, the ion flux is 10 - 100 μA / cm 2 , and the bombardment time is 1 - 3 min. After completion, use plasma-enhanced chemical vapor deposition to deposit SiC on GaN. Place the cleaned sapphire-based GaN into the PECVD reaction chamber, evacuate to the required working pressure, and then introduce the precursor gases required for SiC deposition, including a silicon source (such as silane SiH 4 ) and a carbon source (such as methane CH 4 ) and a dilution gas (such as hydrogen H 2); During the deposition process, the SiC intermediate layer will first fill the two sides of the wide convex structure at the bottom layer to form the first SiC-GaN-SiC structure; then fill the two sides of the convex structure in the intermediate layer to form the second SiC-GaN-SiC structure; finally fill the two sides of the convex structure at the top layer to form the third SiC-GaN-SiC structure and completely cover the GaN. Gas flow rate: SiH 4 : 20 sccm, CH 4 : 40 sccm, radio frequency power: 150 W, deposition pressure: 50 - 80 Pa, deposition temperature: 500 °C, deposition thickness: 120 - 150 nm.

[0038] The third step is to thin the SiC intermediate layer of the deposited sapphire-based GaN by laser thinning until the GaN region in the middle of the top layer is exposed, and after completion, select nanodiamond particle polishing liquid for polishing.

[0039] The fourth step is to put the sapphire-based GaN deposited with SiC into the prepared dilute sulfuric acid solution, and put single crystal diamond into the prepared NaOH / H 2 O 2 mixed solution. The concentration of the dilute sulfuric acid solution is 30%, and the mixture of NaOH / H 2 O 2 consists of 20 mL of 15% NaOH solution, 20 mL of 25% H 2 O 2 solution and 50 mL of deionized water. The soaking temperature is 60 °C and the time is 10 min.

[0040] The fifth step is to wash the soaked GaN epitaxial wafer and single crystal diamond with deionized water and dry them with nitrogen, then put them in an inert gas environment to contact each other, apply pressure while annealing at high temperature to bond them. Annealing temperature: 100 °C, applied pressure: 1 MPa, bonding time: 2 h.

[0041] The sixth step is to mechanically separate the sapphire substrate and GaN / diamond, remove the sapphire substrate, and obtain the target GaN / diamond.

[0042] Example 3, this example provides a preparation method for GaN / diamond bonding, and the preparation method is as follows: First step: Uniformly coat a layer of photoresist on the surface of Si-based GaN, and perform soft baking (90 °C) for one minute to remove air bubbles. Use a pre-designed layered stepped structure mask, align the mask with the GaN epitaxial wafer, perform ultraviolet light exposure (exposure energy is 120 mJ / cm²), perform post-baking (100 °C, 1 min) after exposure to cure the photoresist, then develop it with a developer (such as sodium carbonate solution or KMPR solution) to remove the photoresist in the unexposed area, expose the GaN surface and put it into a plasma etching machine, and use a mixed gas of Cl 2 and Ar for plasma etching. Cl 2 Flow rate: 50 - 100 sccm, Ar flow rate: 20 - 50 sccm, RF power: 300 - 500 W, etching temperature: 150 °C. The etching process is divided into three steps to form three-layer stepped structures respectively: the etching depth of the first layer is 50 nm to form the wide convex structure at the bottom layer; the etching depth of the second layer is 25 nm to form the convex structure in the middle layer; the etching depth of the third layer is 15 nm to form the convex structure at the top layer, and the width decreases from bottom to top. After reaching the required etching depth, wash away the photoresist residue with deionized water, and then use a photoresist remover (N-methylpyrrolidone) to remove the remaining photoresist. After completion, ultrasonically clean the sapphire-based GaN epitaxial wafer and single-crystal diamond with acetone, methyl ethyl ketone, and deionized water in sequence for 5 - 10 min.

[0043] Second step: Bombard the surface of Si-based GaN with an Ar ion beam to remove the surface oxide layer and activate the surface. Ion energy: 2 - 3 keV, ion flow rate: 20 - 80 μA / cm 2 , bombardment time: 1 - 3 min. After completion, deposit AlN on GaN using magnetron sputtering. Put the cleaned Si-based GaN into the vacuum chamber of the magnetron sputtering system, evacuate to the required working pressure, load the AlN sputtering target material, start the sputtering power supply to generate a magnetic field and ions, make argon (Ar) ions bombard the AlN target, sputter AlN atoms or molecules from the target surface, and deposit them on the GaN substrate. During the deposition process, the AlN intermediate layer will first fill the two sides of the wide convex structure at the bottom layer to form the first layer of AlN-GaN-AlN structure; then fill the two sides of the convex structure in the middle layer to form the second layer of AlN-GaN-AlN structure; finally fill the two sides of the convex structure at the top layer to form the third layer of AlN-GaN-AlN structure and cover all of the GaN. Ar flow rate: 50 - 80 sccm, sputtering power: 300 - 500 W, sputtering pressure: 2 - 5 Pa, sputtering temperature: 400 - 450 °C, sputtering thickness: 90 - 120 nm.

[0044] In the third step, the sapphire-based GaN after deposition is thinned by laser to thin the AlN intermediate layer until the GaN region in the middle of the uppermost layer is exposed. After completion, an alkaline solution containing Al 2 O 3 particles is selected for polishing.

[0045] In the fourth step, the Si-based GaN deposited with AlN is placed in the prepared dilute hydrochloric acid solution, and the single-crystal diamond is placed in the prepared NH 4 OH / H 2 O 2 mixed solution. The concentration of the dilute hydrochloric acid solution is 20%. The mixture of NH 4 OH / H 2 O 2 consists of 15 mL of 25% NH 4 OH solution, 15 mL of 25% H 2 O 2 solution, and 30 mL of deionized water. The soaking temperature is 60 °C and the time is 10 min.

[0046] In the fifth step, the soaked Si-based GaN and single-crystal diamond are cleaned with deionized water and dried with nitrogen, and then placed in an inert gas environment to contact each other. While annealing at high temperature, pressure is applied to bond them. Annealing temperature: 350 °C, applied pressure: 2 MPa, bonding time: 3 h.

[0047] In the sixth step, the Si substrate and GaN / diamond are separated by laser to remove the Si substrate, and the target GaN / diamond is obtained.

[0048] Working process: First, prepare a single-crystal diamond and a GaN epitaxial wafer, and etch the GaN epitaxial wafer to form a layered stepped structure; second, bombard the GaN with an Ar ion beam to activate its surface, deposit an intermediate layer on the surface, and after deposition, thin the intermediate layer until the middle GaN part is exposed. After thinning, polishing is carried out; then, the GaN and the single-crystal diamond are respectively soaked in acidic and alkaline solutions. After completion, they are brought into contact with each other, pressure is applied, and annealing is carried out at high temperature for bonding; finally, after completion, the substrate of the GaN epitaxial wafer is removed to obtain the required GaN / diamond with interfacial thermal resistance.

[0049] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0050] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard 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 comprises the following steps: S1, preparing a single crystal diamond (4) and GaN (2) grown on a sapphire or Si substrate (1), wherein Ra of the single crystal diamond (4) is less than 10 nm, and Ra of the GaN (2) is less than 5 nm; S2, etching the GaN epitaxial wafer using a mask with a layered step structure to form a layered step structure, and after the etching is completed, ultrasonically cleaning the GaN (2) and the single crystal diamond (4) and drying them with nitrogen; S3, bombarding the surface of GaN (2) with an Ar ion beam to remove the oxide layer and activate the surface of GaN (2), and then growing a buffer layer on the surface of GaN (2), while the buffer layer fills both sides of the step and covers the middle GaN (2); S4, thinning the grown buffer layer to expose the middle region of GaN (2) and polishing; S5, respectively immersing the GaN epitaxial wafer and the single crystal diamond (4) after thinning and polishing in different solutions; S6. The immersed GaN epitaxial wafer and the single crystal diamond (4) are cleaned with deionized water and dried with nitrogen to obtain a sample of the GaN epitaxial wafer and a sample of the single crystal diamond (4). The sample of the GaN epitaxial wafer and the sample of the single crystal diamond (4) are brought into contact with each other and pressure is applied to bond them while annealing at high temperature. 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 S2, the GaN epitaxial wafer is etched into a three-layer stepped structure, and the method of etching into the three-layer stepped structure includes but is not limited to chemical etching, plasma etching and electron beam etching.

3. The method according to claim 2, characterized in that: In S2, the method of etching the GaN epitaxial wafer into a three-layer stepped structure includes: 1) The first layer has an etching depth of 50-70nm, forming a wide convex structure at the bottom layer; 2) The second layer etching depth is 25-40nm, forming a convex structure of the middle layer; 3) The third layer is etched to a depth of 50-120 nm, forming a convex structure on the top layer.

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

5. The method according to claim 1, characterized in that: In S3, the buffer layer grown on the surface of GaN (2) is a SiC or AlN intermediate layer (3).

6. The method according to claim 5, characterized in that: In S3, the method of growing a buffer layer on the surface of GaN (2) includes but is not limited to plasma enhanced chemical vapor deposition and magnetron sputtering.

7. The method according to claim 5, characterized in that: In S3, the method for growing a buffer layer on the surface of GaN (2) 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 middle layer to form a second layer structure; 3) The buffer layer fills both sides of the top convex structure to form the third layer structure and completely covers the GaN (2).

8. 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.

9. The method according to claim 1, characterized in that: In S6, the high temperature annealing is performed at a temperature of 200-350°C, with an applied pressure of 1-2 MPa for 2-3 hours.

10. The method according to claim 1, characterized in that: In S6, the method of removing the substrate on the GaN epitaxial wafer includes but is not limited to mechanical separation and laser separation.

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