Preparation method of semi-polar plane ga n thin film based on van der waals epitaxy, semi-polar plane ga n thin film and application

Abstract

The application discloses a preparation method of a semi-polar surface GaN film based on van der Waals epitaxy, a semi-polar surface GaN film and application, and the preparation method comprises the following steps: preparing a semi-polar surface aluminum nitride as a substrate; preparing a doped graphene layer; transferring the doped graphene layer to the semi-polar surface aluminum nitride; and growing a GaN film on the doped graphene layer by van der Waals epitaxy to obtain the semi-polar surface GaN film. The preparation method of the semi-polar surface GaN film based on van der Waals epitaxy adopts a semi-polar AlN substrate to prepare a semi-polar surface GaN film based on remote epitaxy in van der Waals epitaxy, and boron-doped graphene or nitrogen-doped graphene is adopted, so that the prepared semi-polar surface GaN can eliminate polarization effect, and provides a key material basis for high-performance green / yellow-orange light LEDs, lasers and power electronic devices.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices and nitride thin films, and in particular to a method for preparing a semi-polar GaN thin film on doped graphene based on van der Waals epitaxy, a semi-polar GaN thin film prepared by the preparation method, and applications of the semi-polar GaN thin film in semiconductor devices. Background Art

[0002] Gallium nitride (GaN), as a core material of the third generation of semiconductors, has revolutionary advantages in the fields of power electronics, radio frequency communications, and optoelectronic devices due to its wide bandgap, high breakdown electric field, and high electron saturation drift velocity. However, traditional polar c-plane GaN has two inherent defects: 1. Quantum confined Stark effect (QCSE): The built-in electric field generated by spontaneous polarization and piezoelectric polarization causes band tilting, significantly reducing the electron-hole recombination efficiency and causing the luminous efficiency of green light band devices to drop by 20-30%; 2. High defect density: The lattice mismatch rates of mainstream heterogeneous substrates such as sapphire and silicon with GaN are as high as 16% and 17% respectively, resulting in high dislocation density (>10 8 cm -2 ), which damages the reliability and life of the device.

[0003] Van der Waals epitaxy (VDE) is a groundbreaking crystal growth technique that utilizes two-dimensional materials as buffer layers. Its core innovation lies in leveraging the absence of dangling bonds on the surface of 2D materials, relying solely on weak van der Waals forces to interact with the growing material. This overcomes the rigid constraints of conventional epitaxy, which require a strict lattice match between the substrate and the epitaxial layer. In traditional processes, this lattice mismatch easily leads to defects such as high densities of dislocations. Remote epitaxy offers a unique and sophisticated implementation within the VDE framework. It not only inherits the fundamental principle of VDE, which exploits weak interactions (VDE forces) at the interface of 2D materials, but also cleverly exploits the partial electrical transparency of certain 2D materials, particularly single- and double-layer graphene. This property enables the long-range electrostatic potential of the underlying single crystal substrate to penetrate the 2D layer, remotely guiding and controlling the arrangement of atoms in the epitaxial layer, ultimately achieving the growth of single-crystalline thin films that are highly lattice-aligned with the substrate at the weak VDE interface.

[0004] However, this technology faces significant challenges: Graphene destabilization at high temperatures: At standard GaN metal-organic chemical vapor deposition (MOCVD) temperatures (>1000°C), graphene degrades or structurally breaks down, compromising the integrity of the epitaxial interface. Insufficient penetration of the substrate polarization electric field: Remote epitaxy requires the substrate polarization electric field to penetrate the 2D material layer to guide epitaxial growth, while also shielding the 2D material from interfering with the epitaxial layer.

[0005] Semi-polar surfaces, such as (11-22) gallium nitride, can significantly weaken or even eliminate the polarization electric field, increasing the internal quantum efficiency of green LEDs by 20-30 percentage points, reducing the wavelength blue shift in InGaN quantum wells, and improving wavelength stability. Furthermore, semi-polar surfaces facilitate the introduction of more indium (In) components into InGaN quantum wells without causing severe lattice relaxation or phase separation, thus breaking through the "green gap" limitation faced by traditional c-plane GaN and extending the efficient emission wavelength to green light (530nm) and even the yellow-orange light band (580-600nm). For example, a pure green semiconductor laser (532nm) based on a semi-polar substrate can achieve a 3-5-fold increase in radiative recombination efficiency.

[0006] However, existing methods for preparing semi-polar GaN face a series of severe technical drawbacks that hinder its large-scale application. In terms of heteroepitaxial growth, the main problems include: when growing directly on heterogeneous substrates such as sapphire, lattice mismatch and surface energy anisotropy easily lead to the generation of high-density twin boundaries and stacking faults, resulting in increased dislocation density and deterioration of crystal quality; when growing on silicon substrates, due to the thermal expansion coefficient mismatch of up to 54%, even with the use of off-angle substrates and SiO2 stripe stress buffering technology, the crack-free film thickness is still limited to less than about 1μm. For example, patent CN115377265A discloses a method for growing semi-polar (11-22) face GaN on silicon substrates. However, HVPE, the mainstream method for bulk single crystals, has a high cost bottleneck, low raw material utilization, and high cost for large-size substrates. In addition, when the wafer size is expanded, the radial temperature gradient and uneven gas flow field cause the crystallization quality to deteriorate. For example, patent CN102119243A discloses the use of hydride vapor phase epitaxy (HVPE) to grow planar non-polar {1-100}m planes and semi-polar {11-22} gallium nitride.

[0007] There is also an existing patent CN119685935A, which discloses a method for remote epitaxial growth of a nitride film on a silicon substrate, a nitride film, and a semiconductor device, which can realize remote epitaxial growth of a nitride film on a silicon substrate.

[0008] This method involves nitriding a silicon substrate to form a Si3N4 layer, which is then covered with a single layer of graphene for nitride film growth. However, this method has the following fundamental flaws: Graphene's high-temperature structural instability: Under the high-temperature environment of the MOCVD process (>1000°C), carbon-carbon bond breakage and hydrogen etching of graphene produce high-density vacancy defects, which reduce the epitaxial interface coverage and destroy the integrity of lattice information transmission; and Si3N4's weak polarizability: The spontaneous polarization strength of Si3N4 is less than 6.2% of that of AlN, and its polarization electric field penetration is less than 10%, causing the interface binding energy to fall into the van der Waals epitaxial range, making remote epitaxy impossible.

[0009] The disclosure of the above background technology content is only used to assist in understanding the inventive concept and technical solution of the present invention. It does not necessarily belong to the prior art of the present invention. In the absence of clear evidence showing that the above content has been disclosed before the application date of the present invention, the above background technology should not be used to evaluate the novelty and creativity of the present invention. Summary of the Invention

[0010] In view of this, the present invention provides a method for preparing a semi-polar GaN thin film based on van der Waals epitaxy, which can overcome the problems of the prior art.

[0011] In order to achieve the above object, the technical solution adopted by the present invention is:

[0012] A method for preparing a semi-polar GaN thin film based on van der Waals epitaxy comprises the following steps:

[0013] preparing a semi-polar aluminum nitride substrate;

[0014] preparing a doped graphene layer;

[0015] Transferring the doped graphene layer onto the semi-polar aluminum nitride;

[0016] A GaN film is grown on the doped graphene layer by van der Waals epitaxial growth to obtain the semi-polar surface GaN film.

[0017] According to some preferred embodiments of the present invention, the semi-polar surface aluminum nitride is semi-polar (11-22) surface aluminum nitride.

[0018] According to some preferred embodiments of the present invention, the van der Waals epitaxy is remote epitaxy, the doped graphene layer is a boron-doped graphene layer or a nitrogen-doped graphene layer, and the doped graphene layer is a single-layer graphene.

[0019] According to some preferred embodiments of the present invention, the boron-doped graphene layer is prepared by the following method:

[0020] The copper foil is placed in a quartz furnace tube, and CH4, H2, and B2H6 gases are introduced to grow graphene at a pressure of 1.5-2.5 Torr to obtain a boron-doped graphene layer.

[0021] According to some preferred embodiments of the present invention, the flow ratio of the B2H6 gas to the CH4 gas is 0.8-1.2:50.

[0022] According to some preferred embodiments of the present invention, the nitrogen-doped graphene layer is prepared by the following method:

[0023] The copper foil is placed in a quartz furnace tube, and CH4, H2, and NH3 gases are introduced to grow graphene at a pressure of 1.5-2.5 Torr to obtain a nitrogen-doped graphene layer.

[0024] According to some preferred implementation aspects of the present invention, the flow ratio of the NH3 gas to the CH4 gas is 0.8-1.2:25.

[0025] Doping graphene with boron atoms can effectively address the problems of graphene's high-temperature instability and insufficient penetration of the substrate's polarization electric field. Undoped graphene severely degrades above 1000°C, while boron doping can increase its temperature tolerance to over 1100°C. This is primarily attributed to the strong covalent bonds formed between boron atoms and the carbon skeleton, which inhibit lattice reconstruction at high temperatures. Boron's electron-deficient nature shifts graphene's Fermi level downward by 0.6 eV, forming p-type semiconductor properties and enhancing charge transfer with polar substrates. Nitrogen-doped atoms also exhibit unique advantages in remote epitaxial growth of GaN, making them particularly irreplaceable in the preparation of semipolar GaN. Compared to boron-doped graphene, which relies primarily on strong covalent bonds to achieve high-temperature stability at 1100°C, N-Gr enhances its oxidation resistance through its pyridinic nitrogen / graphitic nitrogen structure, resulting in a longer lifetime in ammonia environments at 1050-1080°C and a better fit for GaN MOCVD growth. In terms of nucleation control, the lone pair electrons of the N atom undergo long-range hybridization with the substrate orbitals, which increases the adsorption energy of Ga atoms, increases the nucleation density, and reduces the dislocation density.

[0026] According to some preferred embodiments of the present invention, before introducing CH4, H2, and B2H6 gases into the quartz furnace tube, the copper foil is annealed: the copper foil is placed in the quartz furnace tube and annealed for 15-25 minutes at 1000-1100°C and 8-12 mL / min of H2 atmosphere. Annealing is used to remove surface contamination and oxides.

[0027] In some embodiments, the boron-doped graphene layer is prepared by the following steps:

[0028] Place the copper foil in a quartz tube furnace and anneal it at 1000-1100°C in a H2 atmosphere of 8-12 mL / min for 15-25 min;

[0029] Graphene was grown for 35-45 minutes at a pressure of 1.5-2.5 Torr using 4-6 mL / min of CH₄, 70-90 mL / min of H₂, and B₂H₆ gases. The borane-to-methane ratio was 0.8-1.2:50. Borane (B₂H₆) gas was introduced during the CVD graphene growth process, achieving atomic-level uniformity through gaseous catalytic doping, ultimately yielding boron-doped monolayer graphene.

[0030] In some embodiments, the nitrogen-doped graphene is also grown on a copper foil by a chemical vapor deposition (CVD) method, and the nitrogen-doped graphene layer is prepared by the following steps:

[0031] The copper foil is placed in a quartz tube furnace and annealed at 1000-1100℃ under an H2 atmosphere of 8-12mL / min for 15-25min.

[0032] The graphene is grown under a CH4 flow of 4-6mL / min, an H2 flow of 70-90mL / min, and an NH3 gas and a pressure of 1.5-2.5Torr for 35-45min. The gas flow ratio of ammonia to methane is 0.8-1.2:25, and finally a nitrogen-doped single-layer graphene is obtained. In the process of CVD growth of graphene, the ammonia gas is introduced to realize the embedding of nitrogen atoms into the graphene lattice by gas-phase catalysis, and the nitrogen-doped graphene is obtained.

[0033] According to some preferred embodiments of the present application, the transferring comprises the following steps: covering the surface of the doped graphene layer with PMMA, then immersing it in a FeCl3 solution to remove the copper foil; then covering the doped graphene layer with PMMA onto the semi-polar plane aluminum nitride substrate, with one side of the doped graphene layer close to the substrate, and finally removing the PMMA.

[0034] According to some preferred embodiments of the present application, the van der Waals epitaxial growth of the GaN thin film comprises the following steps:

[0035] Under the condition of a temperature of 800-900℃, an ammonia gas with a flow rate of 5000-10000sccm, a trimethyl gallium with a flow rate of 20-50sccm, and a carrier gas are introduced, and the reaction is carried out for 10-30min to grow a GaN nucleation layer.

[0036] Under the condition of a temperature of 1000-1100℃, an NH3 gas with a flow rate of 8000-12000sccm, a TMGa gas with a flow rate of 30-90sccm, and a carrier gas are introduced, and the reaction is carried out for 150-200min to make the nucleation layer merge to form a GaN layer with a thickness of 3-5μm, and a GaN thin film is obtained.

[0037] According to some preferred embodiments of the present application, the carrier gas comprises a nitrogen gas with a flow rate of 200-700sccm and a hydrogen gas with a flow rate of 30-70sccm.

[0038] The present application also provides a semi-polar plane GaN thin film prepared by the above preparation method and an application of the semi-polar plane GaN thin film in a semiconductor device, such as an epitaxial layer for a semiconductor device.

[0039] Due to the application of the above technical solution, the present invention has the following advantages compared with the existing technology: the preparation method of the semi-polar plane GaN thin film based on van der Waals epitaxy of the present invention adopts a semi-polar AlN substrate to prepare the semi-polar plane GaN thin film based on remote epitaxy in van der Waals epitaxy, and uses boron-doped graphene or nitrogen-doped graphene. The prepared semi-polar plane GaN can eliminate the polarization effect and provide a key material foundation for high-performance green / yellow-orange light LEDs, lasers and power electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0041] Figure 1 This is a process flow chart of a method for preparing a semi-polar GaN thin film based on van der Waals epitaxy according to an embodiment of the present invention;

[0042] Figure 2 The stable atomic configuration and charge density contour map of graphene / AlN (11-22) with different numbers of layers provided by the embodiments of the present invention;

[0043] Figure 3 Figure (a) shows the stable atomic structure models of GaN (11-22) / AlN (11-22), GaN (11-22) / SLG / AlN (11-22), GaN (11-22) / BLG / AlN (11-22), GaN (11-22) / TLG / AlN (11-22), and GaN (11-22) / TLG; Figure (b) shows the interface binding energy corresponding to different numbers of graphene layers;

[0044] Figure 4 This is a Raman spectrum of a boron-doped graphene layer bonded to a semi-polar aluminum nitride layer in Example 1 of the present invention;

[0045] Figure 5 This is a scanning electron microscope image of the GaN nucleation layer grown by remote epitaxial growth for 10 minutes in Example 1 of the present invention;

[0046] Figure 6 This is the XRD spectrum after the nucleation layer is grown when preparing the GaN film in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0048] Van der Waals epitaxial GaN thin films on semi-polar surfaces such as (11-22) aluminum nitride (AlN) can solve both the polarization effect and the lattice mismatch problem:

[0049] 1) Suppressing the polarization electric field: The built-in electric field strength of the semi-polar GaN is reduced by more than 80%, significantly weakening the QCSE and improving the quantum efficiency of green and deep ultraviolet LEDs.

[0050] 2) Lattice matching optimization: The lattice constant difference between AlN and GaN is only 2.4% (much lower than sapphire’s 16%), and their thermal expansion coefficients are similar, reducing epitaxial stress and the risk of crack formation.

[0051] 3) Surface energy regulation: The atomic arrangement of the (11-22) plane of semi-polar AlN has anisotropic step flow, which promotes the directional migration of GaN atoms and improves the crystallization quality of the film.

[0052] However, the current growth of semi-polar GaN mainly relies on sapphire patterned substrates or silicon substrate bevel cutting technology, but there are still limitations:

[0053] 1) Sapphire substrate: poor electrical and thermal conductivity, difficult cleavage processing, and insufficient device thermal management capabilities.

[0054] 2) Silicon substrate: Thermal mismatch causes cracks, and the silicon (113) surface and the GaN (11-22) surface need to be precisely matched at a tilt angle of 58.4°, and the process tolerance is small.

[0055] 3) Remote epitaxial compatibility: The polar surface of traditional c-plane AlN intensifies the graphene interface reaction, while semi-polar AlN can reduce the interfacial charge accumulation and improve the stability of the two-dimensional interlayer.

[0056] In addition, doping graphene with boron atoms can effectively address the problems of graphene's high-temperature instability and insufficient penetration of the substrate's polarization electric field. Undoped graphene severely degrades above 1000°C, while boron doping can increase its temperature tolerance to over 1100°C. This is mainly attributed to the strong covalent bonds formed between boron atoms and the carbon skeleton, which inhibit lattice reconstruction at high temperatures. Boron's electron-deficient nature shifts graphene's Fermi level downward by 0.6 eV, forming p-type semiconductor properties and enhancing charge transfer capabilities with polar substrates. Nitrogen-doped atoms also exhibit unique advantages in remote epitaxial growth of GaN, and are particularly irreplaceable in the preparation of semi-polar GaN. Compared to boron-doped graphene, which relies primarily on strong covalent bonds to achieve high-temperature stability at 1100°C, N-Gr enhances its oxidation resistance through its pyridinic nitrogen / graphitic nitrogen structure, resulting in a longer lifespan in ammonia environments at 1050-1080°C and a better fit for GaN MOCVD growth. In terms of nucleation control, the lone pair electrons of the N atom undergo long-range hybridization with the substrate orbitals, which increases the adsorption energy of Ga atoms, increases the nucleation density, and reduces the dislocation density.

[0057] Therefore, the present invention provides a method for preparing a semi-polar GaN epitaxial layer by van der Waals epitaxy on doped graphene, which has low dislocation density, high interface stability and peelable properties, and is a key path to breaking through the performance bottleneck of GaN devices.

[0058] like Figure 1 As shown, the method for preparing a semi-polar GaN thin film based on van der Waals epitaxy of the present invention comprises the following steps:

[0059] Step S1: Prepare substrate

[0060] A semipolar (11-22) aluminum nitride substrate was prepared.

[0061] Step S2: preparing a doped graphene layer

[0062] The doped graphene layer is a single layer, and is preferably a boron-doped graphene layer or a nitrogen-doped graphene layer.

[0063] The boron-doped graphene layer is prepared by the following steps:

[0064] The copper foil was annealed in a quartz tube furnace at 1000-1100°C in an 8-12 mL / min H2 atmosphere for 15-25 minutes. Graphene was then grown for 35-45 minutes in a mixture of 4-6 mL / min CH4, 70-90 mL / min H2, and B2H6 gases at a pressure of 1.5-2.5 Torr, with a borane to methane gas flow ratio of 0.8-1.2:50. Borane (B2H6) gas was introduced during the CVD graphene growth process, achieving atomic-level uniformity through gaseous catalytic doping, ultimately yielding boron-doped monolayer graphene.

[0065] Nitrogen-doped graphene is also grown on copper foil via chemical vapor deposition (CVD), specifically by the following steps: placing the copper foil in a quartz tube furnace and annealing it for 15-25 minutes at 1000-1100°C in an H2 atmosphere of 8-12 mL / min; growing graphene for 35-45 minutes in an atmosphere of 4-6 mL / min CH4, 70-90 mL / min H2, and NH3 gas at a pressure of 1.5-2.5 Torr. The gas flow ratio of ammonia to methane is 0.8-1.2:25, ultimately yielding nitrogen-doped single-layer graphene. Ammonia gas is introduced during the CVD graphene growth process, and nitrogen atoms are embedded into the graphene lattice through gas-phase catalysis to yield nitrogen-doped graphene.

[0066] Step S3: Transferring the doped graphene layer to the substrate

[0067] Doped graphene can be transferred from a metal catalyst substrate to a (11-22)AlN substrate. The substrate's electrostatic potential field penetrates the graphene and redistributes the surface charge, forming a potential distribution that matches the substrate's lattice period. This helps control the orientation of the epitaxial layer and achieve better epitaxial layer quality.

[0068] Specifically, the transfer includes the following steps: covering the surface of the doped graphene layer with PMMA, then immersing it in a FeCl3 solution and removing the copper foil; then covering the doped graphene layer with PMMA on a semi-polar aluminum nitride substrate, with one side of the doped graphene layer close to the substrate, and finally removing the PMMA.

[0069] Preferably, the doped graphene layer is a single layer of graphene with a thickness of about 0.34 nm.

[0070] Step S4: Remote epitaxial growth of GaN thin film

[0071] A GaN film is remotely epitaxially grown on the doped graphene layer to obtain a semi-polar surface GaN film.

[0072] Specifically, at a temperature of 800-900° C., ammonia gas with a flow rate of 5000-10000 sccm, trimethyl gallium with a flow rate of 20-50 sccm, and a carrier gas are introduced for a reaction time of 10-30 minutes to grow a GaN nucleation layer;

[0073] At a temperature of 1000-1100° C., NH 3 with a flow rate of 8000-12000 sccm, TMGa with a flow rate of 30-90 sccm, and a carrier gas are introduced for 150-200 minutes to allow the nucleation layer to merge to form a GaN layer with a thickness of 3-5 μm, thereby obtaining a GaN film.

[0074] The carrier gas includes nitrogen with a flow rate of 200-700 sccm and hydrogen with a flow rate of 30-70 sccm.

[0075] The semi-polar GaN thin film prepared by the above preparation method can be used in semiconductor devices, such as epitaxial layers of semiconductor devices.

[0076] Figure 2 and Figure 3 Schematic diagram showing the principle of remote epitaxial growth of semi-polar aluminum nitride to produce semi-polar GaN thin films. Figure 2 Simulated charge density contour maps at 0.6 Å on the surfaces of two structures, SLG / AlN (11-22) and BLG / AlN (11-22). Figure 2 Figures (a) and (b) are the stable atomic configuration and charge density contour maps of single-layer graphene / m-AlN, respectively; Figures (c) and (d) are the stable atomic configuration and charge density contour maps of double-layer graphene / m-AlN, respectively. Figure 2 In Figure (b), the blue and red colors represent positive and negative charge regions, respectively, both of which are on some top sites (T) of graphene and exist near Al and N atoms. Figure 2 This indicates that the substrate charge density will only be redistributed in the single-layer graphene system. Therefore, in the graphene / AlN (11-22) system, the electrostatic force of the AlN (11-22) substrate can only penetrate one layer of graphene, affecting the pz orbital of the single-layer graphene and presenting its own charge density distribution trend on its surface.

[0077] When two-dimensional materials are grown on graphene, with van der Waals forces acting in between, this is called van der Waals epitaxy. Regardless of the number of graphene layers, this is van der Waals epitaxy. Remote epitaxy is a type of van der Waals epitaxy that occurs under specific conditions. Figure 3The stable atomic structures of GaN(11-22) / AlN(11-22), GaN(11-22) / SLG / AlN(11-22), GaN(11-22) / BLG / AlN(11-22), GaN(11-22) / TLG / AlN(11-22) and GaN / TLG are optimized by DFT simulation, and the interface binding energy corresponding to different graphene layers is calculated. 0-layer graphene is ZLG, 1-layer graphene is SLG, 2-layer graphene is SLG, 3-layer graphene is TLG, and multi-layer graphene is MLG. When the number of graphene layers gradually increases from 0 to multi-layer, it represents the transition from traditional covalent epitaxy to remote epitaxy and then to van der Waals epitaxy, and the interface binding energy of GaN and AlN changes from -2.36 eV to -0.279 eV and then to -0.141 eV. When the number of graphene layers is single-layer, the substrate polarization field partially penetrates, and the interface binding energy is between covalent bond and van der Waals force. When the number of graphene layers is greater than or equal to 2, the interface binding energy changes little, between -0.14 and -0.15 eV, at this time the substrate has no force on the epitaxial layer, the polarization field is completely shielded, and the interface binding energy is close to pure van der Waals epitaxy. These results show that one layer of graphene can be penetrated on AlN(11-22) to realize remote epitaxy of GaN.

[0078] Embodiment 1: The preparation method of the semipolar plane GaN thin film prepared based on van der Waals epitaxy in the embodiment comprises the following steps:

[0079] Step S1, preparing a substrate.

[0080] The substrate is a (11-22) AlN substrate.

[0081] Step S2, preparing a boron-doped single-layer graphene layer

[0082] The boron-doped single-layer graphene layer is obtained by growing on a copper foil by a chemical vapor deposition (CVD) method, specifically comprising the following steps: placing the copper foil in a quartz tube furnace, annealing at 1050℃ for 20 min under a H2 atmosphere of 10 mL / min; growing graphene under a CH4 gas flow of 5 mL / min, a H2 gas flow of 80 mL / min, a B2H6 gas flow of 1.6 mL / min and a pressure of 2 Torr for 40 min. That is, during the CVD growth of graphene, borane (B2H6) gas is introduced to realize atomic-level uniformity through gaseous catalytic doping, and finally a boron-doped single-layer graphene is obtained.

[0083] Step S3, transferring the boron-doped single-layer graphene layer to a semipolar plane aluminum nitride

[0084] Boron-doped graphene is transferred to AlN (11-22) by wet method, specifically including the following steps: covering the surface of the boron-doped single-layer graphene layer with PMMA, then immersing it in FeCl3 solution, and removing the copper foil; then covering the boron-doped single-layer graphene layer with PMMA on a semi-polar aluminum nitride substrate, with one side of the boron-doped single-layer graphene layer close to the substrate, and finally removing the PMMA by solvent dissolution. That is, a boron-doped single-layer graphene layer is combined on the semi-polar aluminum nitride, and Raman spectroscopy is performed on it, such as Figure 4 As shown in the figure, we can clearly see the characteristic peaks of graphene: D peak (~1350cm -1 )、G peak(~1580cm -1 ) and 2D peak (~2700 cm -1 ). Through I 2D / I G The ratio of can be used to determine the number of graphene layers after transfer. Figure 4 You can see I 2D / I G >2, which leads to the conclusion that the transferred graphene is a single layer.

[0085] Step S4: Remote epitaxial growth of GaN thin film

[0086] A GaN film is remotely epitaxially grown on a boron-doped single-layer graphene layer using MOCVD technology to obtain a semi-polar surface GaN film.

[0087] Specifically, at a temperature of 800° C., ammonia gas with a flow rate of 5000 sccm, trimethylgallium gas with a flow rate of 20 sccm, and a carrier gas were introduced for a reaction time of 10 minutes to grow a GaN nucleation layer;

[0088] At a temperature of 1000° C., NH 3 with a flow rate of 8000 sccm, TMGa with a flow rate of 30 sccm, and a carrier gas were introduced for 200 minutes to allow the nucleation layer to merge to form a GaN layer, thereby obtaining a GaN thin film.

[0089] The carrier gas includes nitrogen with a flow rate of 200 sccm and hydrogen with a flow rate of 30 sccm.

[0090] The traditional graphene surface nucleation is highly random, resulting in large differences in crystal domain size and many defects when merging. The wrinkle-guided directional nucleation is equivalent to "natural lithography", making the spacing between crystal nuclei more uniform. The most critical advantage lies in the control of dislocation density - when crystal domains grow laterally at a similar rate, the lattice mismatch at the merging interface is smaller. Figure 5 As shown in FIG, the GaN nuclei in this embodiment are not randomly nucleated, but nucleated along a line, indicating that the GaN nucleation layer is primarily nucleated and grown in the wrinkle area of ​​graphene. XRD analysis of the grown GaN nucleation layer is performed, as shown in FIG. Figure 6The XRD pattern clearly shows characteristic diffraction peaks from the GaN (11-22) crystal plane, along with peaks from the substrate's AlN (11-22) crystal plane and the sapphire (Al2O3) (30-30) crystal plane. This result demonstrates the successful epitaxial growth of a GaN nucleation layer with a semipolar (11-22) orientation on the graphene / AlN (11-22) template.

[0091] Example 2: The method for preparing a semi-polar GaN thin film based on van der Waals epitaxy in this embodiment includes the following steps:

[0092] Step S1: prepare a substrate.

[0093] The substrate is a (11-22)AlN substrate.

[0094] Step S2: preparing a boron-doped single-layer graphene layer

[0095] Boron-doped single-layer graphene was grown on copper foil by chemical vapor deposition (CVD), which included the following steps: placing the copper foil in a quartz tube furnace and annealing it at 1000°C in a 12 mL / min H2 atmosphere for 25 min; 2、 Graphene was grown for 45 minutes at a B2H6 gas flow rate of 1.12 mL / min and a pressure of 1.5 Torr. Borane (B2H6) gas was introduced during the CVD graphene growth process, achieving atomic-level uniformity through gaseous catalytic doping, ultimately yielding boron-doped monolayer graphene.

[0096] Step S3: Transferring the boron-doped single-layer graphene layer to the semi-polar aluminum nitride surface

[0097] Boron-doped graphene is transferred to AlN (11-22) by a wet method, which specifically includes the following steps: covering the surface of the boron-doped single-layer graphene layer with PMMA, then immersing it in a FeCl3 solution and removing the copper foil; then covering the boron-doped single-layer graphene layer with PMMA on a semi-polar aluminum nitride substrate, with one side of the boron-doped single-layer graphene layer close to the substrate, and finally using a solvent to dissolve and remove the PMMA.

[0098] Step S4: Remote epitaxial growth of GaN thin film

[0099] A GaN film is remotely epitaxially grown on a boron-doped single-layer graphene layer using MOCVD technology to obtain a semi-polar surface GaN film.

[0100] Specifically, at a temperature of 850°C, ammonia (NH3) with a flow rate of 8000 sccm, trimethylgallium (TMGa) with a flow rate of 35 sccm, and a carrier gas were introduced for a reaction time of 20 minutes to grow a GaN nucleation layer.

[0101] At a temperature of 1050° C., NH 3 with a flow rate of 10,000 sccm, TMGa with a flow rate of 60 sccm, and a carrier gas were introduced for 180 minutes to allow the nucleation layer to merge to form a GaN layer, thereby obtaining a GaN thin film.

[0102] The carrier gas includes nitrogen with a flow rate of 500 sccm and hydrogen with a flow rate of 50 sccm.

[0103] Example 3: The method for preparing a semi-polar GaN thin film based on van der Waals epitaxy in this embodiment includes the following steps:

[0104] Step S1: prepare a substrate.

[0105] The substrate is a (11-22)AlN substrate.

[0106] Step S2: preparing a boron-doped single-layer graphene layer

[0107] Boron-doped single-layer graphene was grown on copper foil by chemical vapor deposition (CVD), which included the following steps: placing the copper foil in a quartz tube furnace and annealing it at 1100°C in an 8 mL / min H2 atmosphere for 15 min; 2、 Graphene was grown for 35 minutes at a B2H6 gas flow rate of 2.16 mL / min and a pressure of 2.5 Torr. Borane (B2H6) gas was introduced during the CVD graphene growth process, achieving atomic-level uniformity through gaseous catalytic doping, ultimately yielding boron-doped monolayer graphene.

[0108] Step S3: Transferring the boron-doped single-layer graphene layer to the semi-polar aluminum nitride surface

[0109] Boron-doped graphene is transferred to AlN (11-22) by a wet method, which specifically includes the following steps: covering the surface of the boron-doped single-layer graphene layer with PMMA, then immersing it in a FeCl3 solution and removing the copper foil; then covering the boron-doped single-layer graphene layer with PMMA on a semi-polar aluminum nitride substrate, with one side of the boron-doped single-layer graphene layer close to the substrate, and finally using a solvent to dissolve and remove the PMMA.

[0110] Step S4: Remote epitaxial growth of GaN thin film

[0111] A GaN film is remotely epitaxially grown on a boron-doped single-layer graphene layer using MOCVD technology to obtain a semi-polar surface GaN film.

[0112] Specifically, at a temperature of 900° C., ammonia gas with a flow rate of 10,000 sccm, trimethylgallium gas with a flow rate of 50 sccm, and a carrier gas were introduced for a reaction time of 30 minutes to grow a GaN nucleation layer;

[0113] At a temperature of 1100° C., NH 3 with a flow rate of 12,000 sccm, TMGa with a flow rate of 90 sccm, and a carrier gas were introduced for 150 minutes to allow the nucleation layer to merge to form a GaN layer, thereby obtaining a GaN thin film.

[0114] The carrier gas includes nitrogen with a flow rate of 700 sccm and hydrogen with a flow rate of 70 sccm.

[0115] Example 4: The method for preparing a semi-polar GaN thin film based on van der Waals epitaxy in this embodiment is different from that in Example 1 in that step S2 in this embodiment is to prepare a nitrogen-doped single-layer graphene layer, which is also grown on a copper foil by chemical vapor deposition (CVD). The specific preparation steps are as follows:

[0116] The copper foil was annealed in a quartz tube furnace at 1050°C for 20 minutes in a 10 mL / min H2 atmosphere. Graphene was then grown for 40 minutes under a flow rate of 5 mL / min CH4, 80 mL / min H2, and 3.2 mL / min NH3 at a pressure of 2 Torr. Ammonia was introduced during the CVD graphene growth process, allowing nitrogen atoms to be incorporated into the graphene lattice through gas-phase catalysis, resulting in nitrogen-doped monolayer graphene.

[0117] The remaining steps and parameters are basically the same as those in Example 1.

[0118] The method for preparing a semi-polar GaN thin film based on van der Waals epitaxy of the present invention uses a combination of a semi-polar AlN substrate + boron-doped graphene or nitrogen-doped graphene + semi-polar GaN, which respectively have the following advantages:

[0119] Semi-polar AlN reduces interfacial charge, lowering the electrostatic interaction strength between the AlN surface and the graphene layer above. Lower charge accumulation means weaker chemical driving force, effectively suppressing adverse chemical reactions that may occur between AlN and graphene at high temperatures.

[0120] Boron-doped graphene improves thermal stability. Utilizing the strong covalent boron-carbon bond, the thermal stability of graphene is significantly increased to above 1100°C, perfectly matching the high-temperature (1000-1100°C) epitaxial growth requirements of GaN using MOCVD. This prevents the degradation and cracking of traditional graphene at high temperatures, ensuring epitaxial interface integrity and process window.

[0121] Nitrogen-doped graphene enhances its oxidation resistance through the pyridinic nitrogen / graphitic nitrogen structure, extending its lifespan in an ammonia-rich (NH3) environment at 1050-1080°C. Its lone pair electrons undergo orbital hybridization with the semi-polar AlN substrate, significantly increasing the Ga atom adsorption energy and boosting the nucleation density. High-density nucleation induces the annihilation of grain boundary dislocations, further reducing the dislocation density.

[0122] Boron doping not only solves the problem of graphene instability, but its p-type characteristics also enhance the charge transfer ability with the underlying semi-polar AlN substrate, effectively promoting the substrate polarization electric field to penetrate the graphene layer and stably guide the remote epitaxial growth mode; while nitrogen doping focuses on chemical stability and nucleation regulation; the semi-polar AlN substrate and the semi-polar surface GaN have lattice matching and similar thermal expansion coefficients, further reducing dislocation density and epitaxial stress.

[0123] The prepared semi-polar GaN can eliminate the polarization effect and provide a key material basis for high-performance green / yellow-orange LEDs, lasers and power electronic devices.

[0124] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

[0125] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

Claims

1. A method for preparing a semi-polar GaN thin film based on van der Waals epitaxy, characterized in that: The steps include: preparing a semi-polar aluminum nitride substrate; preparing a doped graphene layer; Transferring the doped graphene layer onto the semi-polar aluminum nitride; A GaN film is grown on the doped graphene layer by van der Waals epitaxial growth to obtain the semi-polar surface GaN film.

2. The preparation method according to claim 1, characterized in that The semi-polar surface aluminum nitride is semi-polar (11-22) surface aluminum nitride.

3. The preparation method according to claim 1, characterized in that The van der Waals epitaxy is remote epitaxy; the doped graphene layer is a boron-doped graphene layer or a nitrogen-doped graphene layer.

4. The preparation method according to claim 3, characterized in that The boron-doped graphene layer is prepared by the following method: A copper foil is placed in a quartz furnace tube, and CH4, H2, and B2H6 gases are introduced to grow graphene at a pressure of 1.5-2.5 Torr to obtain a boron-doped graphene layer; the flow ratio of the B2H6 gas to the CH4 gas is 0.8-1.2:

50.

5. The preparation method according to claim 3, characterized in that The nitrogen-doped graphene layer is prepared by the following method: A copper foil is placed in a quartz furnace tube, and CH4, H2, and NH3 gases are introduced to grow graphene at a pressure of 1.5-2.5 Torr to obtain a nitrogen-doped graphene layer; the flow ratio of the NH3 gas to the CH4 gas is 0.8-1.2:

25.

6. The preparation method according to claim 4 or 5, characterized in that Before the gas is introduced into the quartz furnace tube, the copper foil is subjected to annealing treatment: the copper foil is placed in the quartz furnace tube and annealed for 15-25 minutes at 1000-1100° C. and 8-12 mL / min of H 2 atmosphere.

7. The preparation method according to claim 1, characterized in that The transfer comprises the following steps: covering the surface of the doped graphene layer with PMMA, then immersing it in a FeCl3 solution and removing the copper foil; then covering the doped graphene layer with PMMA on a semi-polar aluminum nitride substrate with one side of the doped graphene layer close to the substrate, and finally removing the PMMA.

8. The preparation method according to claim 1, characterized in that The van der Waals epitaxial growth of GaN thin film comprises the following steps: At a temperature of 800-900° C., ammonia gas at a flow rate of 5000-10000 sccm, trimethylgallium gas at a flow rate of 20-50 sccm, and a carrier gas are introduced for a reaction time of 10-30 minutes to grow a GaN nucleation layer; At a temperature of 1000-1100° C., NH 3 with a flow rate of 8000-12000 sccm, TMGa with a flow rate of 30-90 sccm, and a carrier gas are introduced for 150-200 minutes to allow the nucleation layer to merge to form a GaN layer, thereby obtaining a GaN thin film.

9. A semipolar GaN thin film, characterized in that: The semipolar GaN thin film is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the semipolar GaN thin film according to claim 9 in a semiconductor device.

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