Diamond-based gallium nitride epitaxial substrate structure and preparation method thereof

Abstract

The present invention relates to a diamond-based gallium nitride epitaxial substrate structure and a preparation method thereof. The preparation method comprises: step 1: preparing an aluminum nitride nucleation layer on a diamond substrate; step 2: growing a graphene layer on a copper foil surface; step 3: transferring the graphene layer from the copper foil to the aluminum nitride nucleation layer; and step 4: epitaxially growing a gallium nitride epitaxial layer on the graphene layer to obtain a diamond-based gallium nitride epitaxial substrate structure. The preparation method of the diamond-based gallium nitride epitaxial substrate structure of the present invention first forms a layer of aluminum nitride nucleation layer on a diamond substrate by low-temperature magnetron sputtering, then transfers the graphene layer to the aluminum nitride nucleation layer by transfer, and then performs gallium nitride epitaxial growth. The gallium nitride layer obtained by epitaxy has a good lattice orientation, and the aluminum nitride nucleation layer plays a lattice correction role.

Description

Technical Field

[0001] The present invention belongs to the field of microelectronics technology, and in particular relates to a substrate structure for diamond-based gallium nitride epitaxy and a preparation method thereof. Background Art

[0002] The third-generation wide bandgap nitride semiconductor material has a large bandgap width and has superior properties such as high breakdown electric field, high thermal conductivity, high electron saturation rate, and strong radiation resistance. Therefore, semiconductor devices made of wide bandgap nitride semiconductor materials can not only operate stably at higher temperatures, but are also more reliable under high voltage and high frequency conditions. In addition, they can achieve higher operating capabilities with less power consumption.

[0003] As the performance of GaN-based devices continues to improve, high-quality GaN epitaxial materials are becoming increasingly important. Traditional mainstream processes involve growing GaN directly on diamond substrates. However, due to the severe lattice mismatch between the diamond substrate and the nitride and the high dislocation density, the resulting GaN epitaxial films are of poor quality and cannot be used for device fabrication.

[0004] To improve the quality of GaN films grown on diamond substrates, the following methods are usually used: magnetron sputtering aluminum nitride on the diamond substrate and then performing GaN film epitaxy. Since the temperature of magnetron sputtering aluminum nitride is relatively low, it is easily destroyed during the high-temperature growth process, resulting in its effect not being well reflected; photolithography is performed on the surface of the diamond substrate to obtain a patterned substrate to promote GaN nucleation and obtain a GaN epitaxial layer film. However, the cost of photolithography is high and it is not suitable for industrial-scale production applications. In addition, the quality of the prepared GaN film is poor and remains only in the experimental stage. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a substrate structure for diamond-based gallium nitride epitaxy and a method for preparing the same. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] The present invention provides a method for preparing a substrate structure for diamond-based gallium nitride epitaxy, comprising:

[0007] Step 1: Prepare an aluminum nitride nucleation layer on a diamond substrate;

[0008] Step 2: growing a graphene layer on the surface of the copper foil;

[0009] Step 3: transferring the graphene layer from the copper foil to the aluminum nitride nucleation layer;

[0010] Step 4: epitaxially growing a gallium nitride epitaxial layer on the graphene layer to obtain a diamond-based gallium nitride epitaxial substrate structure.

[0011] In one embodiment of the present invention, step 1 includes:

[0012] Step 1.1: Pre-treating the diamond substrate and the Al target respectively;

[0013] Step 1.2: Deposit an aluminum nitride nucleation layer on the pretreated diamond substrate using a magnetron sputtering process in a mixed atmosphere of argon and nitrogen, wherein the sputtering power is 45-60 W, the deposition time is 15-65 min, and the thickness of the aluminum nitride nucleation layer is 15-100 nm.

[0014] In one embodiment of the present invention, step 1.1 includes:

[0015] Step 1.1.1: heating the diamond substrate to 500-600° C. and bombarding the diamond substrate with reverse sputtering in a mixed atmosphere of argon and nitrogen to remove the oxide layer on the surface of the diamond substrate and nitride the surface of the diamond substrate;

[0016] Step 1.1.2: Pre-sputtering the Al target in an argon atmosphere to remove the oxide layer and impurities on the surface of the Al target.

[0017] In one embodiment of the present invention, in step 1.1.2, the pre-sputtering process is: the sputtering power is 45-60W, and the sputtering time is 4-10 minutes.

[0018] In one embodiment of the present invention, step 3 includes:

[0019] Step 3.1: spin coating and curing to form a PMMA film on the surface of the graphene layer to obtain a Cu foil / graphene / PMMA material;

[0020] Step 3.2: Soaking the Cu foil / graphene / PMMA material in an ammonium persulfate solution to remove the copper foil and obtain a graphene / PMMA material;

[0021] Step 3.3: After the graphene / PMMA material in the ammonium persulfate solution is transferred to deionized water for immersion, the graphene / PMMA material is picked up using a diamond substrate having an aluminum nitride nucleation layer to obtain a graphene / PMMA-covered substrate;

[0022] Step 3.4: Soak the substrate prepared in step 3.3 in acetone solution to remove the PMMA film;

[0023] Step 3.5: Transfer the graphene-covered diamond substrate from the acetone solution to an ethanol solution, let it stand, and then remove it and air dry it to complete the transfer of the graphene layer.

[0024] In one embodiment of the present invention, in step 3.1, the spin coating process is: spin coating at a rotation speed of 800-1200 rpm for 15-40s, and then spin coating at a rotation speed of 2500-3400 rpm for 60-120s; the curing process is: drying at a drying temperature of 50-80°C for 20-45min.

[0025] In one embodiment of the present invention, step 4 includes:

[0026] Step 4.1: Under an ammonia atmosphere, the reaction chamber temperature was raised to 900°C and the reaction chamber pressure was 300 mbar;

[0027] Step 4.2: Hydrogen, ammonia, and gallium source were introduced sequentially, the reaction chamber temperature was raised to 1100°C, and the reaction chamber pressure was maintained at 300 mbar;

[0028] Step 4.3: epitaxially growing a GaN epitaxial layer on the graphene layer using a MOCVD process in an atmosphere of hydrogen, ammonia, and a gallium source;

[0029] Step 4.4: After the reaction chamber temperature is lowered to room temperature, a substrate structure for diamond-based gallium nitride epitaxy is obtained.

[0030] The present invention provides a substrate structure for diamond-based gallium nitride epitaxy, comprising: a diamond substrate, an aluminum nitride nucleation layer, a graphene layer and a gallium nitride epitaxial layer stacked in sequence from bottom to top.

[0031] In one embodiment of the present invention, the thickness of the aluminum nitride nucleation layer is 15-100 nm.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention provides a method for preparing a substrate structure for diamond-based gallium nitride epitaxy. First, an aluminum nitride nucleation layer is formed on a diamond substrate by low-temperature magnetron sputtering. A graphene layer is then transferred onto the aluminum nitride nucleation layer by transfer, and then gallium nitride epitaxial growth is performed. The epitaxially grown gallium nitride layer has a good lattice orientation, and the aluminum nitride nucleation layer plays a lattice correction role.

[0034] 2. The method for preparing a diamond-based GaN epitaxial substrate structure of the present invention uses a graphene layer and a magnetron-sputtered aluminum nitride nucleation layer as a composite insertion layer. The composite insertion layer is used to effectively block dislocations. The graphene layer increases the probability of GaN nucleation while protecting the underlying aluminum nitride nucleation layer, releasing the stress between the diamond substrate and the GaN epitaxial layer, reducing the dislocation density, and realizing the use of the graphene layer to promote the growth of heteroepitaxial GaN layers on a diamond substrate, thereby improving the quality of the GaN epitaxial layer.

[0035] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of a method for preparing a diamond-based gallium nitride epitaxial substrate structure provided by an embodiment of the present invention;

[0037] Figure 2 1 is a schematic cross-sectional view of a substrate structure for diamond-based gallium nitride epitaxy provided by an embodiment of the present invention;

[0038] Figure 3 It is a schematic diagram of the substrate structure after the graphene layer is transferred to the aluminum nitride nucleation layer provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description of a diamond-based gallium nitride epitaxial substrate structure and a preparation method thereof proposed in accordance with the present invention, in conjunction with the accompanying drawings and specific embodiments.

[0040] The aforementioned and other technical contents, features, and effects of the present invention are clearly presented in the following detailed description of the specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a deeper and more specific understanding of the technical means and effects adopted by the present invention to achieve the intended purpose can be obtained. However, the accompanying drawings are provided for reference and illustration purposes only and are not intended to limit the technical solutions of the present invention.

[0041] Example 1

[0042] See Figure 1 , Figure 1 This is a flow chart of a method for preparing a diamond-based gallium nitride epitaxial substrate structure provided by an embodiment of the present invention. As shown in the figure, the method for preparing a diamond-based gallium nitride epitaxial substrate structure of this embodiment includes:

[0043] Step 1: Prepare an aluminum nitride nucleation layer on a diamond substrate;

[0044] In this example, a magnetron sputtering device model PRO Line PVD 75 was used to form an aluminum nitride nucleation layer on a diamond substrate. The target-substrate distance of the device was fixed at 22 cm. A metal Al target with a purity of 99.999% was used. To prevent contamination by air impurities, the vacuum level of the sputtering chamber was evacuated to 1E before reactive sputtering. -6Torr, to ensure that the impurity gas content in the chamber is low enough.

[0045] Specifically, step 1 includes:

[0046] Step 1.1: Pre-treating the diamond substrate and the Al target respectively; specifically, comprising:

[0047] Step 1.1.1: Heat the diamond substrate to 500-600°C and, in a mixed atmosphere of argon and nitrogen, perform reverse sputtering bombardment on the diamond substrate to remove the oxide layer on the surface of the diamond substrate and nitride the surface of the diamond substrate;

[0048] In this embodiment, after the diamond substrate is heated to the target temperature, a mixture of high-purity argon and high-purity nitrogen is introduced, and the diamond substrate is sputtered for 10-20 minutes using a radio frequency source with a power of 45-60W to remove the oxide layer on the surface of the substrate and nitride the surface of the substrate.

[0049] Step 1.1.2: In an argon atmosphere, pre-sputter the Al target to remove the oxide layer and impurities on the Al target surface.

[0050] In this embodiment, after the diamond substrate is pretreated, pure argon gas is introduced to pre-sputter the Al target to remove the oxide layer and impurities on the surface of the Al target. The pre-sputtering process is as follows: the sputtering power is 45-60W and the sputtering time is 4-10 minutes.

[0051] Step 1.2: Deposit an aluminum nitride nucleation layer on the pretreated diamond substrate using a magnetron sputtering process in a mixed atmosphere of argon and nitrogen, wherein the sputtering power is 45-60 W, the deposition time is 15-65 min, and the thickness of the aluminum nitride nucleation layer is 15-50 nm.

[0052] In this embodiment, a mixed gas of argon and nitrogen is introduced in a ratio of 1:1.

[0053] Step 2: growing a graphene layer on the surface of the copper foil;

[0054] In this embodiment, a graphene layer is grown on the surface of the copper foil using a CVD process, and the number of graphene layers is 1-5. 2 Graphene is a new material in which hybrid-connected carbon atoms are tightly stacked into a single-layer two-dimensional honeycomb lattice structure. It has excellent optical, electrical and mechanical properties.

[0055] Step 3: Transferring the graphene layer from the copper foil to the aluminum nitride nucleation layer;

[0056] Specifically, step 3 includes:

[0057] Step 3.1: spin coating and curing to form a PMMA film on the surface of the graphene layer to obtain a Cu foil / graphene / PMMA material;

[0058] In this embodiment, the spin coating process is: spin coating at a speed of 800-1200 rpm for 15-40s, and then spin coating at a speed of 2500-3400 rpm for 60-120s; the curing process is: drying at a drying temperature of 50-80°C for 20-45min.

[0059] Step 3.2: Soaking the Cu foil / graphene / PMMA material in an ammonium persulfate solution to remove the copper foil and obtain a graphene / PMMA material;

[0060] Specifically, the Cu foil / graphene / PMMA material is immersed in a 64-68 g / L ammonium persulfate solution for 12-24 hours, and the copper foil is removed to obtain the graphene / PMMA material.

[0061] Step 3.3: After the graphene / PMMA material in the ammonium persulfate solution is transferred to deionized water for immersion, the graphene / PMMA material is picked up using a diamond substrate having an aluminum nitride nucleation layer to obtain a graphene / PMMA-covered substrate;

[0062] Specifically, the graphene / PMMA material in the ammonium persulfate solution was transferred to deionized water using a clean glass slide. After soaking for 60-180 minutes, the graphene / PMMA material was picked up using a diamond substrate with an aluminum nitride nucleation layer to obtain a substrate covered with graphene / PMMA.

[0063] Step 3.4: Soak the substrate prepared in step 3.3 in acetone solution to remove the PMMA film;

[0064] Specifically, place the substrate prepared in step 3.3 in a glass container, add an appropriate amount of acetone and dissolve the PMMA film, replace the acetone after 40-70 minutes, and continue for 3-5 times. The last time, soak the sample in acetone for 12-24 hours to fully remove the PMMA residue.

[0065] Step 3.5: Transfer the graphene-covered diamond substrate from the acetone solution to an ethanol solution, let it stand, and then remove it and air dry to complete the transfer of the graphene layer.

[0066] Specifically, the graphene-covered substrate is transferred from the acetone solution to the ethanol solution and allowed to stand for 30-60 minutes, then taken out and naturally dried to complete the transfer of the graphene layer.

[0067] Step 4: epitaxially growing a gallium nitride epitaxial layer on the graphene layer to obtain a diamond-based gallium nitride epitaxial substrate structure. Specifically, step 4 includes:

[0068] Step 4.1: Under an ammonia atmosphere, the reaction chamber temperature was raised to 900°C and the reaction chamber pressure was 300 mbar;

[0069] Step 4.2: Hydrogen, ammonia, and gallium source were introduced sequentially, the reaction chamber temperature was raised to 1100°C, and the reaction chamber pressure was maintained at 300 mbar;

[0070] Step 4.3: epitaxially growing a GaN epitaxial layer on the graphene layer using a MOCVD process in an atmosphere of hydrogen, ammonia, and a gallium source;

[0071] In this embodiment, the flow rate of the gallium source TMGa is 300 sccm, the flow rate of the ammonia gas is 10500 sccm, the epitaxial growth time is 40 minutes, and the thickness of the gallium nitride epitaxial layer is 1-3 μm.

[0072] Step 4.4: After the reaction chamber temperature is lowered to room temperature, a substrate structure for diamond-based gallium nitride epitaxy is obtained.

[0073] In the method for preparing the diamond-based GaN epitaxial substrate structure of this embodiment, an aluminum nitride nucleation layer is first formed on a diamond substrate by low-temperature magnetron sputtering. A graphene layer is then transferred onto the aluminum nitride nucleation layer by transfer, and then GaN epitaxial growth is performed. The epitaxially grown GaN layer has a good lattice orientation, and the aluminum nitride nucleation layer plays a lattice correction role.

[0074] Example 2

[0075] This embodiment uses different aluminum nitride nucleation layer thicknesses as an example to specifically illustrate the preparation method in Example 1.

[0076] 1. Prepare a substrate structure for diamond-based gallium nitride epitaxy with an aluminum nitride nucleation layer having a thickness of 25 nm, comprising the following steps:

[0077] Step a. preparing a 25 nm aluminum nitride nucleation layer on a diamond substrate;

[0078] (a1) A PRO Line PVD 75 magnetron sputtering system was used to form an aluminum nitride nucleation layer on a diamond substrate. The target-substrate distance of the system was fixed at 22 cm. A metal Al target with a purity of 99.999% was used. To prevent contamination by air impurities, the sputtering chamber was vacuumed to 1E before reactive sputtering. -6 Torr, to ensure that the impurity gas content in the chamber is low enough.

[0079] (a2) The substrate temperature was set to 550°C. After the diamond substrate reached the target temperature, a mixture of high-purity argon and high-purity nitrogen was introduced and the diamond substrate was sputtered for 15 minutes using a 50W RF source to remove the oxide layer on the surface of the diamond substrate and nitride the surface of the diamond substrate.

[0080] (a3) Pure argon gas was introduced to pre-sputter the Al target using a DC 50 W sputtering technique for 5 min to remove the oxide layer and impurities on the Al target surface.

[0081] (a4) A mixture of argon and nitrogen is introduced at a ratio of 1:1. The sputtering power is set to 50 W. Pre-sputtering is performed for 5 minutes to allow the target voltage and current to reach a stable state to ensure a relatively constant film deposition rate. The baffle is then opened to begin depositing the AlN film. The deposition process lasts for 20 minutes, forming an aluminum nitride nucleation layer with a thickness of approximately 25 nm on the diamond substrate.

[0082] Step b. growing a graphene layer on the surface of the copper foil and transferring the graphene layer to the aluminum nitride nucleation layer.

[0083] (b1) Graphene is grown on the surface of copper foil using CVD process.

[0084] (b2) A PMMA film was spin-coated on the surface of the graphene layer at an initial rotation speed of 1000 rpm for 20 s, and then at a rotation speed of 3000 rpm for 60 s. The PMMA-spin-coated Cu foil was then placed on a baking table and dried at 70°C for 20 min to solidify the PMMA film, thereby obtaining a Cu foil / graphene / PMMA material.

[0085] (b3) The Cu foil / graphene / PMMA material was placed upward in a 64 g / L ammonium persulfate solution and immersed for 12 h. The copper foil was removed to obtain the graphene / PMMA material.

[0086] (b4) Using a clean glass slide, the graphene / PMMA material in the ammonium persulfate solution is transferred to deionized water. After soaking for 60-180 min, the graphene / PMMA material is scooped out using a diamond substrate having an aluminum nitride nucleation layer to obtain a graphene / PMMA-covered substrate.

[0087] (b5) Place the substrate prepared in (b4) in a glass container and add an appropriate amount of acetone to dissolve the PMMA film. Replace the acetone after 60 minutes, and repeat this process three times. Finally, soak the sample in acetone for 12 hours to fully remove the PMMA residue.

[0088] (b4) The graphene-covered diamond substrate was transferred from the acetone solution to an ethanol solution and allowed to stand for 30 min. The substrate was then removed and allowed to dry naturally, completing the transfer of the graphene layer.

[0089] Step c. epitaxially growing a gallium nitride epitaxial layer on the graphene layer.

[0090] (c1) In an ammonia atmosphere, the reaction chamber temperature was raised to 900°C and the reaction chamber pressure was 300 mbar. Subsequently, hydrogen, ammonia, and a gallium source were introduced in sequence, and the reaction chamber temperature was raised to 1100°C and the pressure was maintained at 300 mbar.

[0091] (c2) epitaxially growing a 1-3 μm gallium nitride epitaxial layer on the graphene layer using an MOCVD process in an atmosphere of hydrogen, ammonia, and a gallium source, wherein the flow rate of the gallium source TMGa is 300 sccm; and the flow rate of the ammonia is 10500 sccm.

[0092] (c3) After the reaction chamber temperature is lowered to room temperature, the sample is taken out to obtain a substrate structure for diamond-based gallium nitride epitaxy.

[0093] 2. Prepare a substrate structure for diamond-based gallium nitride epitaxy with an aluminum nitride nucleation layer having a thickness of 100 nm, comprising the following steps:

[0094] Step a. preparing a 100 nm aluminum nitride nucleation layer on a diamond substrate;

[0095] (a1) A PRO Line PVD 75 magnetron sputtering system was used to form an aluminum nitride nucleation layer on a diamond substrate. The target-substrate distance of the system was fixed at 22 cm. A metal Al target with a purity of 99.999% was used. To prevent contamination by air impurities, the sputtering chamber was vacuumed to 1E before reactive sputtering. -6 Torr, to ensure that the impurity gas content in the chamber is low enough.

[0096] (a2) The substrate temperature was set to 550°C. After the diamond substrate reached the target temperature, a mixture of high-purity argon and high-purity nitrogen was introduced and the diamond substrate was sputtered for 15 minutes using a 50W RF source to remove the oxide layer on the surface of the diamond substrate and nitride the surface of the diamond substrate.

[0097] (a3) Pure argon gas was introduced to pre-sputter the Al target using a DC 50 W sputtering technique for 5 min to remove the oxide layer and impurities on the Al target surface.

[0098] (a4) A mixture of argon and nitrogen was introduced at a ratio of 1:1, and the sputtering power was set to 50 W. Pre-sputtering was performed for 5 minutes to allow the target voltage and current to reach a stable state to ensure a relatively constant film deposition rate. The baffle was then opened to begin deposition of the AlN film. The deposition process lasted for 65 minutes, forming an aluminum nitride nucleation layer with a thickness of approximately 100 nm on the diamond substrate.

[0099] Step b. growing a graphene layer on the surface of the copper foil and transferring the graphene layer to the aluminum nitride nucleation layer.

[0100] (b1) Graphene is grown on the surface of copper foil using CVD process.

[0101] (b2) A PMMA film was spin-coated on the surface of the graphene layer at an initial rotation speed of 1000 rpm for 20 s, and then at a rotation speed of 3000 rpm for 60 s. The PMMA-spin-coated Cu foil was then placed on a baking table and dried at 70°C for 20 min to solidify the PMMA film, thereby obtaining a Cu foil / graphene / PMMA material.

[0102] (b3) The Cu foil / graphene / PMMA material was placed upward in a 64 g / L ammonium persulfate solution and immersed for 12 h. The copper foil was removed to obtain the graphene / PMMA material.

[0103] (b4) Using a clean glass slide, the graphene / PMMA material in the ammonium persulfate solution is transferred to deionized water. After soaking for 60-180 min, the graphene / PMMA material is scooped out using a diamond substrate having an aluminum nitride nucleation layer to obtain a graphene / PMMA-covered substrate.

[0104] (b5) Place the substrate prepared in (b4) in a glass container and add an appropriate amount of acetone to dissolve the PMMA film. Replace the acetone after 60 minutes, and repeat this process three times. Finally, soak the sample in acetone for 12 hours to fully remove the PMMA residue.

[0105] (b4) The graphene-covered diamond substrate was transferred from the acetone solution to an ethanol solution and allowed to stand for 30 min. The substrate was then removed and allowed to dry naturally, completing the transfer of the graphene layer.

[0106] Step c. epitaxially growing a gallium nitride epitaxial layer on the graphene layer.

[0107] (c1) In an ammonia atmosphere, the reaction chamber temperature was raised to 900°C and the reaction chamber pressure was 300 mbar. Subsequently, hydrogen, ammonia, and a gallium source were introduced in sequence, and the reaction chamber temperature was raised to 1100°C and the pressure was maintained at 300 mbar.

[0108] (c2) epitaxially growing a 1-3 μm gallium nitride epitaxial layer on the graphene layer using an MOCVD process in an atmosphere of hydrogen, ammonia, and a gallium source, wherein the flow rate of the gallium source TMGa is 300 sccm; and the flow rate of the ammonia is 10500 sccm.

[0109] (c3) After the reaction chamber temperature is lowered to room temperature, the sample is taken out to obtain a substrate structure for diamond-based gallium nitride epitaxy.

[0110] The method for preparing a diamond-based gallium nitride epitaxial substrate structure of this embodiment uses a graphene layer and a magnetron-sputtered aluminum nitride nucleation layer as a composite insertion layer. The composite insertion layer is used to effectively block dislocations. The graphene layer increases the probability of gallium nitride nucleation while protecting the aluminum nitride nucleation layer underneath, releasing the stress between the diamond substrate and the gallium nitride epitaxial layer, reducing the dislocation density, and realizing the use of the graphene layer to promote the growth of a heteroepitaxial gallium nitride layer on a diamond substrate, thereby improving the quality of the gallium nitride epitaxial layer.

[0111] Example 3

[0112] This embodiment provides a substrate structure for diamond-based gallium nitride epitaxy. Figure 2 and Figure 3 , Figure 2 1 is a schematic cross-sectional view of a substrate structure for diamond-based gallium nitride epitaxy provided by an embodiment of the present invention; Figure 3 This is a schematic diagram of the substrate structure after the graphene layer is transferred to the aluminum nitride nucleation layer, according to an embodiment of the present invention. As shown in the figure, the substrate structure for diamond-based gallium nitride epitaxy in this embodiment comprises: a diamond substrate, an aluminum nitride nucleation layer, a graphene layer, and a gallium nitride epitaxial layer, stacked in order from bottom to top. In this embodiment, the aluminum nitride nucleation layer is 15-100 nm thick.

[0113] In the substrate structure of diamond-based gallium nitride epitaxy in this embodiment, graphene is evenly covered on the surface of the magnetron sputtered aluminum nitride nucleation layer. On the one hand, because the magnetron sputtered aluminum nitride nucleation layer has a low temperature, it will decompose during the high-temperature MOCVD growth of the gallium nitride epitaxial layer and will not play a nucleation role. After the addition of the graphene layer, the graphene layer effectively protects the magnetron sputtered aluminum nitride layer. On the other hand, because the graphene layer can form a weak van der Waals force with the magnetron sputtered aluminum nitride nucleation layer, it can release the stress generated by the lattice mismatch between the aluminum nitride nucleation layer and the gallium nitride epitaxial layer. At the same time, the graphene layer can also act as a dislocation barrier, reducing the dislocation density, realizing the use of graphene to promote the nucleation of heteroepitaxial gallium nitride on diamond, and improving the quality of the gallium nitride epitaxial material on diamond.

[0114] It should be noted that, in this document, the terms "comprises", "includes" or any other variations are intended to cover non-exclusive inclusion, so that an article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed. In the absence of further restrictions, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the article or device comprising the element. The orientation or positional relationship indicated by "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0115] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a substrate structure for diamond-based gallium nitride epitaxy, characterized in that: include: Step 1: Prepare an aluminum nitride nucleation layer on a diamond substrate; The step 1 comprises: Step 1.1: Pre-treating the diamond substrate and the Al target respectively; Step 1.1 includes: Step 1.1.1: Heat the diamond substrate to 500-600 o C. In a mixed atmosphere of argon and nitrogen, reverse sputtering bombards the diamond substrate to remove the oxide layer on the surface of the diamond substrate and nitride the surface of the diamond substrate; Step 1.1.2: Pre-sputtering the Al target in an argon atmosphere to remove the oxide layer and impurities on the surface of the Al target; in step 1.1.2, the pre-sputtering process is as follows: the sputtering power is 45-60W, and the sputtering time is 4-10 minutes; Step 1.2: Depositing an aluminum nitride nucleation layer on the pretreated diamond substrate using a magnetron sputtering process in an argon and nitrogen mixed atmosphere, wherein the sputtering power is 45-60 W and the deposition time is 15-65 minutes. The thickness of the aluminum nitride nucleation layer is 15-100 nm. Step 2: growing a graphene layer on the surface of the copper foil; Step 3: transferring the graphene layer from the copper foil to the aluminum nitride nucleation layer, with the graphene layer and the magnetron sputtered aluminum nitride nucleation layer serving as a composite insertion layer; Step 4: epitaxially growing a gallium nitride epitaxial layer on the graphene layer to obtain a diamond-based gallium nitride epitaxial substrate structure.

2. The method for preparing a substrate structure for diamond-based gallium nitride epitaxy according to claim 1, characterized in that: The step 3 includes: Step 3.1: spin coating and curing to form a PMMA film on the surface of the graphene layer to obtain a Cu foil / graphene / PMMA material; Step 3.2: Soaking the Cu foil / graphene / PMMA material in an ammonium persulfate solution to remove the copper foil and obtain a graphene / PMMA material; Step 3.3: After the graphene / PMMA material in the ammonium persulfate solution is transferred to deionized water for immersion, the graphene / PMMA material is picked up using a diamond substrate having an aluminum nitride nucleation layer to obtain a graphene / PMMA-covered substrate; Step 3.4: Soak the substrate prepared in step 3.3 in acetone solution to remove the PMMA film; Step 3.5: Transfer the graphene-covered diamond substrate from the acetone solution to an ethanol solution, let it stand, and then remove it and air dry it to complete the transfer of the graphene layer.

3. The method for preparing a diamond-based gallium nitride epitaxial substrate structure according to claim 2, wherein: In step 3.1, the spin coating process is: spin coating at a speed of 800-1200 rpm for 15-40s, and then spin coating at a speed of 2500-3400 rpm for 60-120s; the curing process is: drying at a temperature of 50-80 o C, drying for 20-45 min.

4. The method for preparing a diamond-based gallium nitride epitaxial substrate structure according to claim 1, characterized in that: The step 4 comprises: Step 4.1: Under ammonia atmosphere, increase the temperature of the reaction chamber to 900 o C, reaction chamber pressure is 300 mbar; Step 4.2: Introduce hydrogen, ammonia and gallium source in sequence, and raise the temperature of the reaction chamber to 1100 o C, reaction chamber pressure maintained at 300 mbar; Step 4.3: epitaxially growing a GaN epitaxial layer on the graphene layer using a MOCVD process in an atmosphere of hydrogen, ammonia, and a gallium source; Step 4.4: After the reaction chamber temperature is lowered to room temperature, a substrate structure for diamond-based gallium nitride epitaxy is obtained.

5. A substrate structure for diamond-based gallium nitride epitaxy, characterized in that: The method for preparing a diamond-based gallium nitride epitaxial substrate structure according to any one of claims 1 to 4 is used to prepare the diamond-based gallium nitride epitaxial substrate structure, wherein the diamond-based gallium nitride epitaxial substrate structure comprises: a diamond substrate, an aluminum nitride nucleation layer, a graphene layer, and a gallium nitride epitaxial layer stacked in sequence from bottom to top.

6. The diamond-based gallium nitride epitaxial substrate structure according to claim 5, characterized in that: The thickness of the aluminum nitride nucleation layer is 15-100 nm.

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