Gallium nitride film and graphene van der Waals epitaxial gallium nitride film growth method

Abstract

The invention provides a gallium nitride thin film and a graphene van der Waals epitaxial gallium nitride thin film growth method. The method comprises the following steps: step 102, manufacturing a first AlN buffer layer on a substrate; step 103, transferring a two-dimensional material layer on the first AlN buffer layer; step 104, manufacturing a second AlN buffer layer on the two-dimensional material layer; and step 105, forming a GaN material thin film on the second AlN buffer layer. The invention also provides the gallium nitride film prepared by the method. The gallium nitride thin film is high in crystal quality, can be peeled off and is suitable for preparing a high-efficiency light-emitting diode.

Description

Technical Field

[0001] The invention relates to a gallium nitride film and a graphene van der Waals epitaxial gallium nitride film growth method, belonging to the technical field of semiconductor materials and devices. Background Art

[0002] Currently, gallium nitride (GaN)-based materials and devices have been widely used in various fields such as display, communication and lighting. In order to reduce production costs, foreign substrates (such as sapphire, silicon and silicon carbide) are often selected as substrates for the growth of GaN and other group III nitrides. However, there is a lattice mismatch and thermal mismatch between the nitride epilayer and the foreign substrate, which can lead to a high dislocation density and high residual stress in the GaN film, thus affecting the performance of gallium nitride devices. Therefore, the urgency of finding a method to reduce the negative impact of foreign substrates is self-evident.

[0003] In recent years, some two-dimensional materials have been used to grow materials such as GaN. This technology is based on van der Waals epitaxy (VDWE) of two-dimensional materials. Among the common two-dimensional materials, graphene has become the majority choice due to its excellent stability, in-plane hexagonal lattice arrangement, and more mature preparation technology. When graphene is used as an intermediate layer, the epitaxial layer and the substrate are separated, and the lattice mismatch and thermal mismatch can be ignored in theory. More importantly, there is only a weak van der Waals force on the surface of the two-dimensional material, so that the epitaxial layer can be easily peeled off from the substrate by mechanical peeling. The peeled epitaxial layer can be transferred to any other substrate for the subsequent device production, which is conducive to cost saving.

[0004] Although van der Waals epitaxy has advantages in device fabrication, the dislocation density in GaN grown by this method is still as high as 10 9 cm -2. For some devices, especially laser diodes, a lower dislocation density is usually required. Kim et al. (Kim, Y., Cruz, S., Lee, K. et al. Remote epitaxy through graphene enables two-dimensional material-based layer transfer. Nature 544, 340–343 (2017). https: / / doi.org / 10.1038 / nature22053) reported a technique called remote epitaxy, which forms a single-crystalline gallium nitride film on an intermediate graphene layer through remote atomic interactions between the substrate and the epitaxial layer. According to their research, the polarity strength of the substrate material is the key to the growth of GaN on two-dimensional materials. Nitride has a hexagonal wurtzite structure, and polarity is one of its important properties. Therefore, III-nitride native substrates or templates are a good choice for remote epitaxy. More importantly, when III-nitride is used as a growth substrate, the remote interaction between atoms can guide the epitaxial layer to form the same atomic arrangement as the substrate. This is beneficial to improve the crystal quality of GaN, especially when the thickness of the epitaxial layer is thin, such as being limited to a few hundred nanometers. Although single-crystalline GaN can be obtained by remote epitaxy, the peeling mechanism is still unclear, and the growth conditions of GaN generally require a high temperature of more than 1000 degrees Celsius, which may cause damage to graphene and lose the van der Waals force between the epitaxial layer and graphene, which will cause the film peeling to fail. Summary of the invention

[0005] In order to solve the problem that the general van der Waals epitaxy has high dislocation density and cannot be simply peeled off by mechanical peeling after the epitaxial growth is completed, the purpose of the present invention is to provide a graphene van der Waals epitaxial gallium nitride material growth method.

[0006] To achieve the above object, the present invention provides a method for growing a graphene van der Waals epitaxial gallium nitride film, which comprises the following steps:

[0007] Step 102, forming a first AlN buffer layer on the substrate;

[0008] Step 103, transferring a two-dimensional material layer onto the first AlN buffer layer;

[0009] Step 104, forming a second AlN buffer layer on the two-dimensional material layer;

[0010] Step 105: forming a GaN material film on the second AlN buffer layer.

[0011] According to a specific embodiment of the present invention, preferably, the method further comprises step 101: cleaning the substrate and removing residual moisture.

[0012] According to a specific embodiment of the present invention, preferably, the substrate is a sapphire substrate, a silicon carbide substrate, a silicon single crystal substrate, a spinel substrate, a silicon carbide substrate or a zinc oxide substrate.

[0013] According to a specific embodiment of the present invention, preferably, the sapphire substrate is a single crystal sapphire substrate.

[0014] According to a specific embodiment of the present invention, preferably, the sapphire substrate is a flat sapphire substrate.

[0015] According to a specific embodiment of the present invention, preferably, the orientation of the sapphire substrate is (0001).

[0016] According to a specific embodiment of the present invention, preferably, the thickness of the sapphire substrate is 300-500 μm, more preferably 410-430 μm.

[0017] According to a specific embodiment of the present invention, in step 102, introducing a first AlN buffer layer before transferring the two-dimensional material layer can improve the crystal quality of the subsequently grown gallium nitride, enhance the polarity strength of the substrate material, and improve the crystal quality of the upper GaN material film.

[0018] According to a specific embodiment of the present invention, preferably, in step 102, the first AlN buffer layer is manufactured by sputtering or MOCVD epitaxial growth.

[0019] According to a specific embodiment of the present invention, preferably, the thickness of the first AlN buffer layer grown by sputtering is 10-100 nm, more preferably 10-20 nm.

[0020] According to a specific embodiment of the present invention, preferably, the first AlN buffer layer grown by sputtering is a polycrystalline AlN material.

[0021] According to a specific embodiment of the present invention, preferably, the orientation of the first AlN buffer layer grown by sputtering is (0001).

[0022] According to a specific embodiment of the present invention, preferably, the thickness of the first AlN buffer layer epitaxially grown by MOCVD is 1-3 μm.

[0023] According to a specific embodiment of the present invention, preferably, the first AlN buffer layer epitaxially grown by MOCVD is a single crystal AlN material.

[0024] According to a specific embodiment of the present invention, preferably, the orientation of the first AlN buffer layer epitaxially grown by MOCVD is (0001).

[0025] According to a specific embodiment of the present invention, preferably, the polarity of the first AlN buffer layer epitaxially grown by MOCVD is Al polarity.

[0026] According to a specific embodiment of the present invention, preferably, in step 103, the two-dimensional material layer is single-crystalline graphene.

[0027] According to a specific embodiment of the present invention, preferably, in step 103, the thickness of the graphene is 1-3 layers.

[0028] According to a specific embodiment of the present invention, preferably, the method of transferring the two-dimensional material layer is wet transfer.

[0029] According to a specific embodiment of the present invention, preferably, the solution used in the wet transfer does not react with the substrate.

[0030] According to a specific embodiment of the present invention, preferably, the wet transfer further comprises: spin coating polymethyl methacrylate onto the surface of the grown two-dimensional material, and heating and curing; more preferably, the curing temperature is 50-150°C.

[0031] According to a specific embodiment of the present invention, preferably, the wet transfer also includes: etching and removing the substrate on which the two-dimensional material is grown, transferring the two-dimensional material with the solidified film from the solution into deionized water for cleaning after etching, transferring and attaching it to the target substrate, drying it, and baking it to remove moisture; then removing the polymethyl methacrylate to obtain a single layer of two-dimensional material, followed by annealing.

[0032] According to a specific embodiment of the present invention, preferably, the process of preparing a single-layer two-dimensional material is repeated to obtain a multi-layer two-dimensional material.

[0033] According to a specific embodiment of the present invention, in step 104, by introducing a second AlN buffer layer on the two-dimensional material layer, the problem that the two-dimensional material is easily damaged by the high temperature of the subsequent growth of gallium nitride can be solved, thereby playing a role in protecting the two-dimensional material layer.

[0034] According to a specific embodiment of the present invention, preferably, in step 104, the second AlN buffer layer is sputtered by a pulsed magnetron sputtering method.

[0035] According to a specific embodiment of the present invention, preferably, the thickness of the second AlN buffer layer grown by pulsed magnetron sputtering is 10-50 nm, more preferably 10-20 nm.

[0036] According to a specific embodiment of the present invention, preferably, the orientation of the second AlN buffer layer obtained by pulsed magnetron sputtering is (0001).

[0037] According to a specific embodiment of the present invention, preferably, step 105 includes: providing a metal gallium source and a nitrogen source, and using MOCVD van der Waals epitaxial growth of a GaN film.

[0038] According to a specific embodiment of the present invention, preferably, a two-step growth method is adopted: firstly, a nucleation layer is grown at a low temperature, and then a GaN material thin film is formed on the second AlN buffer layer by high temperature growth.

[0039] According to a specific embodiment of the present invention, preferably, the thickness of the GaN material film obtained by high temperature growth is 300 nm-3 μm, more preferably 1-3 μm.

[0040] According to a specific embodiment of the present invention, preferably, the method further comprises a step of peeling off the GaN material film.

[0041] The present invention also provides a gallium nitride film, which is prepared by the above method.

[0042] The gallium nitride film provided by the present invention has high crystal quality and can be peeled off, and the film is suitable for the preparation of high-efficiency light-emitting diodes.

[0043] The beneficial effects of the present invention are:

[0044] 1. The preparation method provided by the present invention introduces a first AlN buffer layer under the two-dimensional material layer required for van der Waals epitaxy, which can enhance the polarity strength of the substrate material, play a role in attracting atomic nucleation and regulating atomic arrangement, guide the upper epitaxial layer to form the same atomic arrangement as the substrate, and improve the crystal quality of the upper GaN material film.

[0045] 2. The difficulty in preparing the GaN epitaxial layer is to ensure both the crystal quality and the strippability of the GaN epitaxial layer. However, the GaN epitaxial layer needs to be grown at a high temperature (1040°C), and this temperature will directly cause the graphene to be destroyed and unable to be stripped. If the growth temperature of the GaN epitaxial layer is lowered for the purpose of stripping, the GaN epitaxial layer will become polycrystalline, and a single crystal GaN film cannot be obtained. To solve this problem, the preparation method provided by the present invention introduces a second AlN buffer layer on the two-dimensional material layer required for van der Waals epitaxy, which can protect the two-dimensional material layer, keep it away from the high temperature of the GaN growth process, reduce the degree of decomposition of the two-dimensional material layer, and ensure that the subsequent GaN film can be stripped.

[0046] 3. The GaN film prepared by the preparation method provided by the present invention can be easily peeled off from the substrate by mechanical peeling; the epitaxial layer after peeling can be transferred to any other substrate for device manufacturing, which is simpler than the traditional laser peeling process and is conducive to cost saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic flow chart of the method for preparing the graphene van der Waals epitaxial gallium nitride material of the present invention;

[0048] Figure 2 A schematic diagram of the structure of an epitaxial wafer obtained by the method of the present invention;

[0049] Figure 3 The XRD rocking curve of the (002) surface of the GaN epitaxial layer prepared in Example;

[0050] Figure 4 The XRD rocking curve of the GaN epitaxial layer (102) prepared in the embodiment;

[0051] Figure 5 The SEM scanning image of the surface morphology of the GaN film prepared in the example:

[0052] Figure 6 An optical microscope photograph of the interface region of the GaN film prepared in Example after peeling;

[0053] Figure 7 This is a diagram showing the peeling effect of the GaN film prepared in the comparative example.

[0054] Description of Figure Numbers:

[0055] 1-sapphire substrate, 2-first AlN buffer layer, 3-two-dimensional material layer, 4-second AlN buffer layer, 5-GaN material film. DETAILED DESCRIPTION

[0056] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0057] The present invention provides a method for preparing a graphene van der Waals epitaxial gallium nitride material, the process of which is as follows: Figure 1 As shown, the structure of the prepared epitaxial wafer is as follows Figure 2 The preparation method comprises the following specific steps:

[0058] Step 101, providing a substrate 1, performing preparation work before making a buffer layer, cleaning the substrate surface, removing impurities attached thereon, and facilitating the subsequent making of a first AlN buffer layer 2; after cleaning, removing residual moisture to prevent moisture from interfering with and contaminating subsequent materials.

[0059] In step 101, the material of substrate 1 may be a sapphire substrate. The size of substrate 1 may be 2 inches or 4 inches. The sapphire substrate may be a single crystal sapphire substrate, the sapphire substrate may be a flat sapphire substrate, the orientation of the sapphire substrate may be (0001), and the thickness of the sapphire substrate may be 2-4 μm.

[0060] In step 101, ultrasonic cleaning may be used for cleaning; the cleaning agents used in ultrasonic cleaning may be ultrapure water, acetone, isopropanol and deionized water in this order, and the time may be 5-15 minutes for each cleaning step.

[0061] In step 101, the residual moisture may be removed by blowing with a nitrogen gun or drying in an oven. The drying temperature may be 150-250° C. and the drying time may be 15-120 min.

[0062] Step 102, a first AlN buffer layer 2 is formed on the substrate 1. The first AlN buffer layer 2 can enhance the polarity strength of the substrate material, play a role in attracting atomic nucleation and regulating atomic arrangement, guide the upper epitaxial layer to form the same atomic arrangement as the substrate, and improve the crystal quality of the upper epitaxial GaN material film.

[0063] In step 102 , the first AlN buffer layer 2 may be formed by sputtering or MOCVD epitaxial growth.

[0064] In step 102, when sputtering is used: the thickness of the sputtering-grown first AlN buffer layer 2 can be 10-20 nm, including two end values. The sputtering-grown first AlN buffer layer 2 can be obtained as a polycrystalline AlN material. The sputtering-grown AlN buffer layer can have an orientation of (0001).

[0065] In step 102 , methods for sputtering the first AlN buffer layer 2 include but are not limited to magnetron sputtering, physical vapor deposition (PVD) sputtering, DC sputtering, reactive sputtering, radio frequency sputtering, bias sputtering, high temperature sputtering, vacuum sputtering, etc.

[0066] In step 102, magnetron sputtering can be used to sputter the first AlN buffer layer 2. The RF power of the sputtering can be 100-300W, the gas pressure during sputtering can be maintained at 2-7mTorr, 5-20sccm Ar and 50-100sccm N2 can be introduced during sputtering, the sputtering temperature can be 450-800°C, and the sputtering target material can be pure aluminum.

[0067] In step 102, when MOCVD epitaxial growth is adopted: the thickness of the MOCVD epitaxially grown first AlN buffer layer 2 can be 1-3μm, including two endpoint values, the epitaxially grown first AlN buffer layer 2 can be a single crystal AlN material, the orientation of the epitaxially grown first AlN buffer layer 2 can be (0001), and the polarity of the epitaxially grown first AlN buffer layer 2 can be Al polarity.

[0068] In step 102, MOCVD epitaxial growth of the first AlN buffer layer 2 can use H2 and N2 as carrier gases for the epitaxial process; trimethylaluminum (TMAl) and ammonia (NH3) can be used as Al source and N source respectively; and can be grown at a temperature of 1000-1300°C and a pressure of 30-400Torr.

[0069] Step 103, transferring the two-dimensional material layer 3 onto the first AlN buffer layer 2. The force between the two-dimensional material layers is the van der Waals force, not the covalent bond connection of the traditional three-dimensional material. The two-dimensional material layer 3 is the key to the van der Waals epitaxy, and enables the subsequently grown GaN film 5 to be simply peeled off through the van der Waals force between the two-dimensional material layer 3 and the upper and lower buffer layers;

[0070] In step 103 , the two-dimensional material layer 3 may be single-crystalline graphene.

[0071] In step 103, the graphene material may be synthesized by a CVD method. This method can obtain a graphene material with high integrity and high crystal quality, thereby obtaining an epitaxial layer with high crystal quality and exfoliability in a subsequent growth process.

[0072] The substrate for graphene growth can be a copper (111) substrate; the growth temperature can be 950-1100°C; the carbon source for graphene growth can be methane; 10-500sccm of H2 can be introduced as a carrier gas and mixed with methane to bring methane to the surface of the metal substrate for reaction; the methane flow rate during graphene growth can be 1-30sccm; and the graphene growth time can be 1-3 hours.

[0073] In step 103, the thickness of the graphene can be 1-3 layers.

[0074] In step 103, the method for transferring the two-dimensional material layer 3 can be wet transfer; wherein, the solution used in the wet transfer does not react with the substrate. Wet transfer can use polymethyl methacrylate (PMMA), specifically: use a coating machine to spin-coat it on the surface of the grown two-dimensional material, and then heat and cure PMMA on a heating table, in this way, the adhesion between the two-dimensional material and PMMA can be increased, and the integrity of the two-dimensional material can be protected in the subsequent process; wherein, the curing temperature can be 50-150°C; after heating and curing, the substrate on which the two-dimensional material is grown is etched and removed, and an aqueous solution of ammonium persulfate can be used for etching, and the etching time can be 2-6 hours; after etching, the two-dimensional material with the cured film is slowly transferred from the solution into deionized water for cleaning, and transferred and attached to the target substrate, and dried; wherein, drying can be carried out at room temperature, and the time can be 3-5 hours. In order to better remove moisture, it can be dried at a temperature of 50-200°C for 2-4 hours to remove moisture; after removing moisture, PMMA needs to be removed, leaving only the two-dimensional material. Specifically, the substrate can be placed in acetone and left for a period of time to remove PMMA, at which time a single layer of two-dimensional material is obtained; if a multi-layer two-dimensional material is to be obtained, the above process can be repeated. After the entire transfer process is completed, annealing is performed, which can remove organic matter and oxide residues; the annealing temperature can be 250-500°C, the annealing atmosphere can be 40-250sccm hydrogen and 200-400sccm argon; the annealing time can be 2-4 hours.

[0075] Step 104, forming a second AlN buffer layer 4 on the two-dimensional material layer 3, which can protect the two-dimensional material layer 3 from direct contact with the high temperature of the GaN growth process, reduce the degree of decomposition of the two-dimensional material layer 3, and ensure that the subsequent GaN film can be peeled off;

[0076] In step 104, the second AlN buffer layer 4 can be sputtered by a pulsed magnetron sputtering method, the RF power of the sputtering can be 20-200W, the gas pressure during sputtering can be maintained at 0.1-10Pa, 5-100sccm Ar and 5-100sccm N2 can be introduced during sputtering, the sputtering temperature can be 50-150°C, the pulse frequency can be 20-40kHz; the pulse duty cycle can be 30-60%; the sputtering target material can be pure aluminum. The thickness of the sputtered second AlN buffer layer 4 can be 10-20nm, including two end values; the orientation of the sputtered second AlN buffer layer 4 can be (0001).

[0077] Step 105 , providing a metal gallium source and a nitrogen source, and using MOCVD van der Waals epitaxy to grow a GaN film 5 , using a two-step growth method, first low-temperature growth of a nucleation layer, and then high-temperature growth, to form a GaN material film 5 on the second AlN buffer layer 4 .

[0078] In step 105 , the metal gallium source may include triethylgallium (TEGa) or trimethylgallium (TMGa).

[0079] In step 105, the nitrogen source may include ammonia gas.

[0080] In step 105, the low-temperature nucleation layer can be grown for 5-20 minutes at a temperature of 550-650°C, a TMGa flow rate of 4-15sccm, and an NH3 flow rate of 4000-12000sccm. During the process, the reaction chamber pressure can be 100-400mbar, and nitrogen or hydrogen is used as a carrier gas; the high-temperature growth part can be grown at a temperature of 1000-1100°C, a TMGa flow rate of 20-50sccm, and an NH3 flow rate of 3000-12000sccm. During the process, the reaction chamber pressure can be 100-400mbar, and nitrogen or hydrogen is used as a carrier gas. The thickness of the grown GaN can be 300nm-3μm.

[0081] Example

[0082] This embodiment provides a method for preparing a graphene van der Waals epitaxial gallium nitride material, which specifically includes the following steps:

[0083] Prepare a sapphire single crystal flat substrate with a size of 2 inches; clean the substrate in four steps of ultrapure water, acetone, isopropanol and deionized water, each step takes 10 minutes. After the cleaning work is completed, use a nitrogen air gun to blow away the visible moisture on the surface of the substrate, and then use an oven to dry it, set the temperature to 200℃, and heat it for 1 hour to completely remove the moisture on the surface of the substrate to avoid affecting the subsequent process.

[0084] A first AlN buffer layer is formed on a sapphire substrate by magnetron sputtering: pure aluminum (purity greater than 99.99%) is used as a sputtering target, the sputtering temperature is 600°C, and the sputtering is performed under an environment of 10sccm Ar and 50sccm N2 while maintaining a gas pressure of 4mTorr. The sputtering power is 200W; the thickness of the sputtered first AlN buffer layer is 15nm, and the orientation of AlN is (0001).

[0085] Three layers of single-crystal graphene were obtained as a two-dimensional material layer on the first AlN buffer layer by wet transfer. The synthesis of graphene is as follows: a copper (111) substrate is placed in a CVD device, the temperature is raised to 1050°C, 500 sccm of hydrogen is introduced as a carrier gas, the pressure is controlled to 1Pa, and methane is introduced as a carbon source for graphene growth, the flow rate of methane is 1 sccm, and the growth time is 1 hour; after the growth is completed, the carbon source is stopped and the sample is cooled. The wet transfer process is as follows: first, a layer of polymethyl methacrylate (PMMA) is evenly spin-coated on the surface of graphene using a coater, and the coater is set to rotate at a speed of 1500 for 7 seconds and a speed of 2500 for 60 seconds; after the spin coating is completed, it is cured to form a film supporting the graphene, and the curing temperature is 70°C; then the graphene copper substrate is etched, and an ammonium persulfate aqueous solution is used to etch the cured PMMA graphene therein, at room temperature for 5 hours; after the etching is completed, the PMMA graphene is taken out and soaked in deionized water for cleaning, and then attached to the target substrate and dried; the drying process is carried out at room temperature for 4 hours; after drying, the substrate is placed on a heating table and further dried at a temperature of 60°C for 4 hours to fully remove moisture; after the drying process is completed, the substrate is placed in acetone to remove the PMMA layer, and a layer of graphene is transferred to the target substrate; the wet transfer process is repeated to obtain more layers of graphene. After three transfers, an annealing operation is performed with an annealing temperature of 400° C., a hydrogen flow rate of 100 sccm, an argon flow rate of 400 sccm, and an annealing time of 3.5 hours to remove organic matter and other residues; wherein the solution used in the wet transfer does not react with the amorphous substrate.

[0086] A second AlN buffer layer is produced on the two-dimensional material layer by pulsed magnetron sputtering: pure aluminum (purity greater than 99.99%) is used as the sputtering target, and the sputtering temperature is 75°C. The low temperature can ensure that the two-dimensional material layer below is not damaged by the high temperature; the RF power used for sputtering is 160W, and argon and hydrogen are used as sputtering gases, with an argon flow rate of 50sccm and a hydrogen flow rate of 100sccm; the sputtering pulse frequency is 30kHz, and the pulse duty cycle is selected to be 35%; the gas pressure during sputtering is maintained at 1Pa; the thickness of the sputtered second AlN buffer layer is 20nm, and the orientation of AlN is (0001).

[0087] A GaN material film is grown on the second AlN buffer layer by van der Waals epitaxy, and the substrate after the second AlN buffer layer is formed is placed in an MOCVD device for two-step epitaxial growth: first, the temperature of the growth chamber is adjusted to 576°C, and the pressure is controlled to 400 mbar; nitrogen is introduced as a carrier gas, and ammonia is introduced as a nitrogen source at a flow rate of 5000 sccm, and TMGa is introduced as a gallium source at a flow rate of 5 sccm, and low-temperature growth is performed for 10 minutes; after the growth time is reached, the reaction chamber conditions are adjusted, the temperature is raised to 1040°C, the pressure is maintained at 400 mbar, nitrogen is continued to be introduced as a carrier gas, the flow rates of ammonia are adjusted to 4000 sccm, the flow rates of TMGa are adjusted to 40 sccm, and high-temperature growth is performed for 30 minutes to obtain a GaN film.

[0088] The XRD rocking curves of the (002) and (102) planes of the GaN epitaxial layer prepared in this embodiment are shown in Figures 1 and 2. Figure 3 and Figure 4 As shown, the SEM scanning image of the GaN film surface is as follows Figure 5 As shown. Figure 3-Figure 5 It can be seen that the GaN film has a high crystal quality.

[0089] Figure 6 This is an optical microscope photograph of the interface region of the GaN film prepared in Example after peeling. Figure 6 The brighter area in the middle is the exposed substrate after GaN stripping. Figure 6 It can be seen that the GaN film has good strippability.

[0090] Comparative Example

[0091] In this comparative example, a sapphire single crystal flat substrate is prepared, a first AlN buffer layer is made on the sapphire substrate, and three layers of single crystal graphene as a two-dimensional material layer are obtained on the first AlN buffer layer by wet transfer. These steps are the same as those in the embodiment.

[0092] A second AlN buffer layer is made on the two-dimensional material layer. The process for making the first AlN buffer layer is the same. The production method is magnetron sputtering: pure aluminum (purity greater than 99.99%) is used as the sputtering target, the sputtering temperature is 600°C, and the sputtering is performed under a gas pressure of 4mTorr in an environment of 10sccmAr and 50sccmN2. The sputtering power is 200W; the thickness of the sputtered second AlN buffer layer is 20nm, and the orientation of AlN is (0001).

[0093] A GaN material film is grown on the second AlN buffer layer using van der Waals epitaxial growth method, and the substrate on which the second AlN buffer layer is formed is placed in an MOCVD device for two-step epitaxial growth: first, the temperature of the growth chamber is adjusted to 815°C, and the pressure is controlled to 400 mbar; nitrogen is introduced as a carrier gas, and ammonia is introduced as a nitrogen source at a flow rate of 10,000 sccm; TMGa is introduced as a gallium source at a flow rate of 40 sccm, and low-temperature growth is performed for 2 minutes; after the growth time is reached, the reaction chamber conditions are adjusted, the temperature is raised to 1040°C, the pressure is maintained at 400 mbar, nitrogen is continued to be introduced as a carrier gas, the flow rate of ammonia is adjusted to 5000 sccm, the flow rate of TMGa is maintained unchanged, and high-temperature growth is performed for 45 minutes to obtain a GaN film.

[0094] The GaN film prepared in this comparative example is as follows after peeling: Figure 7 As shown. Figure 7 In the figure, the area circled in the middle has a two-dimensional material layer, and this area cannot be successfully peeled off, indicating that the method of this comparative example cannot obtain a GaN epitaxial layer that has both high crystal quality and can be peeled off.

Claims

1. A method for growing a graphene van der Waals epitaxial gallium nitride film, comprising the following steps: Step 102, forming a first AlN buffer layer on the substrate; Step 103, transferring a two-dimensional material layer onto the first AlN buffer layer; Step 104, forming a second AlN buffer layer on the two-dimensional material layer; Step 105: forming a GaN material film on the second AlN buffer layer.

2. The method according to claim 1, wherein: The method further comprises step 101: cleaning the substrate and removing residual moisture; Preferably, the cleaning is performed by ultrasonic cleaning; More preferably, the ultrasonic cleaning is carried out in the order of ultrapure water, acetone, isopropanol and deionized water, with the cleaning time being 5-15 min respectively; Preferably, the residual moisture is removed by blowing with a nitrogen gun or drying in an oven. The drying temperature is preferably 150-250° C., and the drying time is preferably 15-120 min.

3. The method according to claim 1 or 2, wherein: The substrate is a sapphire substrate; Preferably, the substrate size is 2 inches to 4 inches; Preferably, the sapphire substrate is a single crystal sapphire substrate, a silicon carbide substrate, a silicon single crystal substrate, a spinel substrate, a silicon carbide substrate or a zinc oxide substrate; Preferably, the sapphire substrate is a flat sapphire substrate; Preferably, the orientation of the sapphire substrate is (0001); Preferably, the thickness of the sapphire substrate is 300-500 μm, more preferably 410-430 μm.

4. The method according to claim 1, wherein: In step 102, the first AlN buffer layer is fabricated by sputtering or MOCVD epitaxial growth; Preferably, the thickness of the first AlN buffer layer grown by sputtering is 10-100 nm, more preferably 10-20 nm; Preferably, the first AlN buffer layer grown by sputtering is a polycrystalline AlN material; Preferably, the orientation of the first AlN buffer layer grown by sputtering is (0001); Preferably, the sputtering includes one of magnetron sputtering, physical vapor deposition technology sputtering, DC sputtering, reactive sputtering, radio frequency sputtering, bias sputtering, high temperature sputtering, and vacuum sputtering; Preferably, the sputtering is performed by magnetron sputtering, the RF power of the sputtering is preferably 100-300W, the gas pressure during sputtering is preferably maintained at 2-7mTorr, 5-20sccm Ar and 50-100sccm N2 are preferably introduced during sputtering, the sputtering temperature is preferably 450-800°C, and the sputtering target is preferably pure aluminum; Preferably, the thickness of the first AlN buffer layer epitaxially grown by MOCVD is 1-3 μm; Preferably, the first AlN buffer layer epitaxially grown by MOCVD is a single crystal AlN material; Preferably, the orientation of the first AlN buffer layer epitaxially grown by MOCVD is (0001); Preferably, the polarity of the first AlN buffer layer epitaxially grown by MOCVD is Al polarity; Preferably, the MOCVD epitaxial growth uses H2 and N2 as carrier gases for the epitaxial process; Preferably, the MOCVD epitaxial growth uses trimethylaluminum and ammonia as Al source and N source respectively; Preferably, the temperature of the MOCVD epitaxial growth is 1000-1300° C. and the pressure is 30-400 Torr.

5. The method according to claim 1, wherein: In step 103, the two-dimensional material layer is single-crystalline graphene; Preferably, the graphene is synthesized by a CVD method; Preferably, the substrate on which the graphene is grown is a copper (111) substrate; Preferably, the temperature of the growth of the graphene is 950-1100°C; Preferably, the carbon source for the growth of the graphene is methane; Preferably, during the growth process of the graphene, 10-500 sccm of H2 is introduced as a carrier gas and mixed with methane to bring the methane to the surface of the metal substrate for reaction; more preferably, the methane flow rate during the growth of the graphene is 1-30 sccm; and the graphene growth time is 1-3 hours.

6. The method according to claim 1 or 5, wherein: In step 103, the thickness of the graphene is 1-3 layers; Preferably, the method of transferring the two-dimensional material layer is wet transfer; Preferably, the solution used in the wet transfer does not react with the substrate; Preferably, the wet transfer further comprises: spin coating polymethyl methacrylate onto the surface of the grown two-dimensional material, and heating and curing; more preferably, the curing temperature is 50-150° C.; Preferably, the wet transfer further comprises: etching and removing the substrate on which the two-dimensional material is grown, transferring the two-dimensional material with the solidified film from the solution into deionized water for cleaning, transferring and attaching it to the target substrate, air-drying it, and baking it to remove moisture; then removing the polymethyl methacrylate to obtain a single-layer two-dimensional material, and then performing an annealing treatment; More preferably, the etching is performed using an aqueous solution of ammonium persulfate, and the etching time is 2-6 hours; More preferably, the drying is performed at room temperature for 3-5 hours; More preferably, the drying is performed at 50-200° C. for 2-4 hours; More preferably, the removal of polymethyl methacrylate is carried out in acetone; Preferably, the process of preparing a single layer of two-dimensional material is repeated to obtain a multi-layer two-dimensional material; Preferably, the annealing temperature is 250-500° C., the annealing atmosphere is preferably 40-250 sccm hydrogen and 200-400 sccm argon, and the annealing time is preferably 2-4 hours.

7. The method according to claim 1, wherein: In step 104, a second AlN buffer layer is sputtered by a pulsed magnetron sputtering method; Preferably, the RF power of the pulsed magnetron sputtering is 20-200W; Preferably, the gas pressure of the pulsed magnetron sputtering is maintained at 0.1-10 Pa; Preferably, the pulsed magnetron sputtering is conducted with 5-100 sccm Ar and 5-100 sccm N2; Preferably, the temperature of the pulsed magnetron sputtering is 50-150°C; Preferably, the pulse frequency of the pulsed magnetron sputtering is 20-40kHz; Preferably, the pulse duty cycle of the pulse magnetron sputtering is 30-60%; Preferably, the target material of the pulsed magnetron sputtering is pure aluminum; Preferably, the thickness of the second AlN buffer layer grown by pulsed magnetron sputtering is 10-50 nm, more preferably 10-20 nm; Preferably, the orientation of the second AlN buffer layer obtained by pulsed magnetron sputtering is (0001).

8. The method according to claim 1, wherein: The step 105 includes: providing a metal gallium source and a nitrogen source, and growing a GaN film using MOCVD van der Waals epitaxy; Preferably, a two-step growth method is adopted: firstly, a nucleation layer is grown at a low temperature, and then a GaN material film is formed on the second AlN buffer layer by high-temperature growth; Preferably, the metal gallium source includes triethylgallium or trimethylgallium; Preferably, the nitrogen source comprises ammonia; Preferably, the preparation process of the nucleation layer is to grow for 5-20 minutes at a temperature of 550-650°C, a TMGa flow rate of 4-15 sccm, and an NH3 flow rate of 4000-12000 sccm; the reaction chamber pressure during the process is preferably 100-400 mbar, and nitrogen or hydrogen is used as the carrier gas; Preferably, the high temperature growth process is carried out under the conditions of temperature 1000-1100°C, TMGa flow rate 20-50sccm, and NH3 flow rate 3000-12000sccm; the reaction chamber pressure during the process is preferably 100-400mbar, and nitrogen or hydrogen is used as the carrier gas; preferably, the thickness of the GaN material film obtained by high temperature growth is 300nm-3μm, more preferably 1-3μm.

9. The method according to claim 1, wherein: The method also includes the step of peeling off the GaN material film.

10. A gallium nitride thin film prepared by the method according to any one of claims 1 to 9.

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