Method for preparing gallium oxide heteroepitaxial thin film

Abstract

The present invention belongs to the technical field of gallium oxide film preparation, and discloses a method for preparing a gallium oxide heteroepitaxial film, comprising: preparing ammonium gallium sulfate hydrate in a molten state; preparing a precursor solution using the ammonium gallium sulfate hydrate in a molten state; and annealing in a vacuum environment after spin coating the precursor solution onto a sapphire substrate in stages, thereby obtaining a gallium oxide film with a preferred orientation in a preset crystal direction. The present invention uses ammonium gallium sulfate hydrate to prepare the precursor solution, thereby avoiding the influence of the crystal state on the orientation of the subsequent gallium oxide film. Furthermore, the present invention adopts a staged spin coating method, limits the substrate used to a sapphire substrate, and anneals in a vacuum environment after spin coating, thereby obtaining a gallium oxide film with a preferred orientation in a preset crystal direction. The film has excellent chemical / physical properties and thermal stability, and has important application value in solar-blind photoelectric detection and electronic device manufacturing.

Description

Technical Field

[0001] The invention belongs to the technical field of gallium oxide thin film preparation, and specifically discloses a method for preparing a gallium oxide heteroepitaxial thin film. Background Art

[0002] β-Ga2O3 is considered a promising candidate material for solar-blind photodetectors and high-power devices due to its desirable properties, including a large band gap (4.9 eV) and excellent chemical, mechanical, and thermal stability. Various forms of β-Ga2O3 have been synthesized and studied in the prior art, including bulk, thin films, and nanostructures.

[0003] There are many methods for depositing Ga2O3 thin films, such as metal organic chemical vapor deposition (MOCVD), halide vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), low pressure chemical vapor deposition (LPCVD), pulsed laser deposition (PLD), magnetron sputtering and plasma enhanced chemical vapor deposition (PECVD). However, these methods usually require specific reactions, high vacuum conditions or expensive raw materials, resulting in high costs for preparing Ga2O3 thin films. In terms of practical applications, thin films are considered to have greater advantages than thicker films due to their compatibility with device manufacturing. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing gallium oxide heteroepitaxial thin films to solve the technical problem that the existing preparation of gallium oxide thin films requires specific reactions, high vacuum conditions or expensive raw materials, resulting in high costs for preparing Ga2O3 thin films.

[0005] The present invention provides a method for preparing a gallium oxide heteroepitaxial thin film, comprising:

[0006] Step 1, preparing ammonium gallium sulfate hydrate in a molten state;

[0007] Step 2: preparing a precursor solution using the molten ammonium gallium sulfate hydrate;

[0008] Step 3: spin-coating the precursor solution onto a sapphire substrate in stages and then annealing in a vacuum environment to obtain a gallium oxide thin film with a preferred orientation in a preset crystal direction.

[0009] Preferably, the step 3 specifically includes:

[0010] Step 3.1, spin-coating the precursor solution onto a sapphire substrate in stages;

[0011] Step 3.2: Repeat step 3.1 multiple times to obtain a sapphire substrate covered with a gel layer;

[0012] Step 3.3: Anneal the sapphire substrate with the overlying gel layer in a vacuum environment to obtain a gallium oxide thin film with a preferred orientation in a preset crystal direction.

[0013] Preferably, step 3.1 specifically includes:

[0014] Spin-coat the precursor solution onto the preheated sapphire substrate at a speed of P1 for a continuous spin-coating time of t1 to obtain a first film layer;

[0015] Spin-coat the precursor solution onto the preheated first film layer at a speed of P2 for a continuous spin-coating time of t2 to obtain a second film layer;

[0016] Spin-coat the precursor solution onto the preheated second film layer at a speed of P3 for a continuous spin-coating time of t3 to obtain a third film layer;

[0017] P1 < P2 < P3, and t1 < t2 < t3.

[0018] Preferably, step 3.2 is specifically: Repeat step 3.1 for 5 to 10 times to obtain a sapphire substrate with an overlying gel layer.

[0019] Preferably, the annealing temperature in step 3.3 is 800°C to 900°C, and the annealing time is 1 h to about 1.5 h.

[0020] Preferably, step 2 specifically includes:

[0021] Add an organic solvent and a thickening agent to the molten ammonium gallium sulfate hydrate to prepare a precursor solution.

[0022] Preferably, the organic solvent is ethylene glycol monomethyl ether; the thickening agent is polyacrylamide.

[0023] Preferably, the concentration of the precursor solution is 0.4 mol / L to 0.6 mol / L.

[0024] Preferably, step 1 specifically includes:

[0025] Step 1.1: Prepare gallium sulfate using gallium metal particles and sulfuric acid;

[0026] Step 1.2: Prepare ammonium gallium sulfate hydrate crystals using gallium sulfate and ammonium sulfate;

[0027] Step 1.3: Continuously heat the ammonium gallium sulfate hydrate crystals at a temperature above 60°C to obtain molten ammonium gallium sulfate hydrate. <00000​

[0029] Compared with the prior art, the method for preparing the gallium oxide heteroepitaxial thin film of the present invention has the following beneficial effects:

[0030] The present invention uses ammonium gallium sulfate hydrate to prepare a precursor solution, thereby preventing its crystalline state from affecting the orientation of the subsequent gallium oxide film. Furthermore, the present invention adopts a staged spin coating method, limits the substrate used to a sapphire substrate, and anneals in a vacuum environment after spin coating, thereby obtaining a gallium oxide film with a preferred orientation in a preset crystal direction. The film has excellent chemical / physical properties and thermal stability, and has important application value in solar-blind photoelectric detection and electronic device manufacturing.

[0031] The present invention eliminates the need for expensive gallium nitrate as a precursor to prepare gallium oxide thin films. Instead, high-quality Ga2O3 thin films can be produced using only low-grade gallium metal and inexpensive sulfuric acid, significantly reducing the cost of preparing Ga2O3 thin films from a raw material perspective. Furthermore, the present invention utilizes vacuum annealing at a temperature of only 800°C, further reducing costs from a reaction condition perspective. The present invention's method for preparing heteroepitaxial gallium oxide thin films is simple, easy to operate, low-cost, and produces high-quality gallium oxide films. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 4 is a simple flow chart of a method for preparing a gallium oxide heteroepitaxial thin film according to an embodiment of the present invention.

[0033] Figure 2 Detailed flow chart of the method for preparing a gallium oxide heteroepitaxial thin film according to an embodiment of the present invention.

[0034] Figure 3 1 is an X-ray diffraction (XRD) pattern of the synthetic powder prepared using gallium sulfate and ammonium sulfate in step 1.2 of an embodiment of the present invention.

[0035] Figure 4 This is the X-ray diffraction (XRD) pattern of the β-Ga2O3 powder prepared by using ammonium gallium sulfate hydrate as raw material and sintering at 800°C for 1 hour in an embodiment of the present invention.

[0036] Figure 5Surface scanning electron microscope photographs of β-Ga2O3 films using sapphire as a substrate in an embodiment of the present invention, wherein (a) is a surface scanning electron microscope photograph of the β-Ga2O3 film obtained by repeated spin coating and preheating cycles at 800°C for 5 times and then annealing for 1 hour; (b) is a surface scanning electron microscope photograph of the β-Ga2O3 film obtained by repeated spin coating and preheating cycles at 1000°C for 5 times and then annealing for 1 hour; (c) is a surface scanning electron microscope photograph of the β-Ga2O3 film obtained by repeated spin coating and preheating cycles at 800°C for 10 times and then annealing for 1 hour; (d) is a surface scanning electron microscope photograph of the β-Ga2O3 film obtained by repeated spin coating and preheating cycles at 1000°C for 10 times and then annealing for 1 hour.

[0037] Figure 6 Figure 2 shows the X-ray diffraction patterns of β-Ga2O3 thin films prepared on a (0001) sapphire substrate at annealing temperatures of 800°C and 1000°C after 10 repeated spin coating and preheating cycles according to an embodiment of the present invention.

[0038] Figure 7 (a) is the transmission spectra of the β-Ga2O3 film on the sapphire substrate and the β-Ga2O3 film on the quartz substrate according to an embodiment of the present invention after annealing at 800°C and 1000°C for 1 hour; (b) is the Tauc plot of the transmission curves of the two films corresponding to (a). DETAILED DESCRIPTION

[0039] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0040] An embodiment of the present invention provides a method for preparing a gallium oxide heteroepitaxial thin film, comprising:

[0041] Step 1: preparing ammonium gallium sulfate hydrate in a molten state, specifically comprising:

[0042] Step 1.1: Prepare gallium sulfate using gallium metal particles and sulfuric acid.

[0043] For example, gallium metal particles with a purity of 99.99% and a size of 3-5 mm are added to a beaker, and then sulfuric acid (H2SO4, analytical grade) with a concentration of 80% is slowly added to the beaker and heated to 120°C, wherein the molar ratio of gallium metal particles to sulfuric acid is 2:5. The purpose of maintaining excess sulfuric acid in the embodiment of the present invention is to ensure that the gallium metal particles fully react and dissolve. During the heating process, small hydrogen bubbles gradually form on the surface of the gallium metal particles, and white gallium sulfate (Ga2(SO4)3) precipitates begin to form in the solution. At the same time, some yellow precipitates also appear, which may be sulfur impurities caused by uneven temperature or excessive sulfuric acid. These impurities are removed by repeated filtration (corresponding to Figure 2Step (1) in the above example.

[0044] The chemical formula corresponding to step 1.1 is: .

[0045] Step 1.2: preparing gallium-ammonium sulfate hydrate crystals using gallium sulfate and ammonium sulfate, wherein the molar ratio of gallium sulfate to ammonium sulfate is 1:1-1.5.

[0046] For example, the white gallium sulfate solid obtained after filtration in step 1.1 is dissolved in deionized water. After complete dissolution, ammonium sulfate ((NH4)2SO4, analytical grade) is added, wherein the molar ratio of gallium sulfate to ammonium sulfate is 1:1 to 1.5. Then, an excess of deionized water is added, and the mixture is evaporated, filtered, and washed with deionized water for several times (corresponding to Figure 2 After evaporation and cooling to room temperature, transparent ammonium gallium sulfate hydrate crystals (NH4Ga(SO4)2·12H2O crystals) are formed (corresponding to Figure 2 Step (3) in the previous step).

[0047] The chemical formula corresponding to step 1.2 is:

[0048] .

[0049] Step 1.3: Continuously heating the ammonium gallium sulfate hydrate crystals at a temperature above 60° C. until a molten ammonium gallium sulfate hydrate is obtained.

[0050] In the embodiment of the present invention, the ammonium gallium sulfate hydrate crystals are continuously heated at a temperature above 60° C., and the water evaporates to melt the crystals into a viscous molten liquid, thereby obtaining ammonium gallium sulfate hydrate in a molten state.

[0051] Step 2: preparing a precursor solution using molten ammonium gallium sulfate hydrate, specifically comprising: adding an organic solvent and a thickener to the molten ammonium gallium sulfate hydrate to prepare a precursor solution, stirring the mixture thoroughly, and allowing the mixture to precipitate into a gel (corresponding to Figure 2 Step (4) in the above-mentioned step). The above-mentioned organic solvent is ethylene glycol methyl ether (EGME, CH3OCH2CH2OH); the thickener is polyacrylamide, and its amount is such that the rotational viscosity of the obtained precursor solution at 60°C is 10~100 mPa.s. The concentration of the precursor solution obtained in the embodiment of the present invention is 0.4mol / L~0.6mol / L. In the embodiment of the present invention, the thickener is added to make the rotational viscosity of the precursor solution 10~100 mPa.s, thereby significantly improving the adhesion of the precursor solution to the substrate in the subsequent film formation process and improving the stability of the prepared gallium oxide film.

[0052] Step 3: The precursor solution is spin-coated onto a sapphire substrate in stages and then annealed in a vacuum environment to obtain a gallium oxide film with a preferential orientation in the [–201] direction.

[0053] The sapphire substrate in this embodiment of the present invention is a c-plane sapphire substrate ((0001) plane sapphire substrate). The substrate needs to be cleaned before use. For example, in this embodiment of the present invention, the c-plane sapphire substrate is ultrasonically cleaned for 10 minutes each using acetone, isopropyl alcohol, and deionized water.

[0054] The above step 3 specifically includes:

[0055] Step 3.1, spin-coat the precursor solution onto the sapphire substrate in stages (corresponding to Figure 2 Step (5) in the above process specifically includes:

[0056] Stage 1: Spin-coat the precursor solution onto the preheated sapphire substrate at a rotation speed of P1 for a continuous spin-coating time of t1 to obtain the first film layer;

[0057] The second stage: spin-coating the precursor solution onto the preheated first film layer at a rotation speed of P2 for a continuous spin-coating time of t2 to obtain the second film layer;

[0058] The third stage: spin-coating the precursor solution onto the preheated second film layer at a rotation speed of P3 for a continuous spin-coating time of t3 to obtain the third film layer;

[0059] P1 <P2<P3,t1<t2<t3。

[0060] Exemplarily, P1 is 300rpm~500rpm, for example, 300rpm, 400rpm, 500rpm, etc., preferably 400rpm; P2 is 2000rpm~3000rpm, for example, 2000rpm, 2500rpm, 3000rpm, etc., preferably 2500rpm; P3 is 5000rpm~7000rpm, for example, 5000rpm, 6000rpm, 7000rpm, etc., preferably 6000rpm; the above-mentioned t1 is 8 seconds~12 seconds, for example, 8 seconds, 10 seconds, 12 seconds, etc., preferably 10 seconds; t2 is 15 seconds~25 seconds, for example, 15 seconds, 20 seconds, 25 seconds, etc., preferably 20 seconds; t3 is 25 seconds~35 seconds, for example, 25 seconds, 30 seconds, 35 seconds, etc., preferably 30 seconds.

[0061] The preheating temperature of each stage of spin coating in the embodiment of the present invention is 140°C to 160°C, for example, 140°C, 150°C, 160°C, etc., preferably 150°C; the preheating time of each stage is 8 minutes to 12 minutes, for example, 8 minutes, 10 minutes, 12 minutes, etc., preferably 10 minutes. The above preheating corresponds to Figure 2Step (6) in the embodiment of the present invention. The preheating can promote the removal of solvent and increase the supersaturation of the solution, thereby forming crystal nuclei as seed crystals on the sapphire substrate (corresponding to Figure 2 Step (7) in the above example.

[0062] Step 3.2: Repeat step 3.1 5 to 10 times to obtain a sapphire substrate covered with a uniform gel layer, wherein the thickness of the gel layer is 600 nm to 1.6 μm.

[0063] Step 3.3: Place the sapphire substrate covered with the gel layer in a vacuum environment (5×10 -4 Pa) to obtain a transparent gallium oxide film with a preferred orientation in a preset crystal direction (corresponding to Figure 2 In step (8) of the embodiment of the present invention, the annealing temperature is 800°C to 900°C, for example, 800°C, 850°C, 900°C, etc., preferably 800°C; the annealing time is 1 hour to 1.5 hours, for example, 1 hour, 1.2 hours, 1.5 hours, etc., preferably 1 hour. In the embodiment of the present invention, the preset crystal direction is the [–201] direction.

[0064] The present invention uses ammonium gallium sulfate hydrate to prepare a precursor solution, thereby preventing its crystalline state from affecting the orientation of the subsequent gallium oxide film. Furthermore, the present invention adopts a multi-stage spin coating method, limits the substrate used to a sapphire substrate, and anneals in a vacuum environment after spin coating, thereby obtaining a gallium oxide film with preferential orientation in the [–201] direction. The film has excellent chemical / physical properties and thermal stability, and has important application value in solar-blind photoelectric detection and electronic device manufacturing.

[0065] The effectiveness of the preparation method of the present invention will be verified with more specific examples below.

[0066] To determine Figure 2 The product obtained in step (3) is ammonium gallium sulfate. The crystals obtained in step (3) of the embodiment of the present invention are carefully dried with clean paper, then dried at 60° C. and repeatedly ground into a white powder for XRD analysis.

[0067] Figure 3The XRD pattern of the white powder (upper trace) and the standard powder diffraction file (PDF) data (International Center for Diffraction Data / Powder Diffraction File [ICDD / PDF], number 00-07-0018, lower trace) are shown. A comparison of the XRD patterns of the synthesized powder shows excellent agreement with the standard PDF data, confirming the successful synthesis of the target compound, ammonium gallium sulfate (NH4Ga(SO4)2). The XRD pattern of the synthesized powder exhibits multiple distinct diffraction peaks in the range of 10° to 80°. The positions and intensities of these diffraction peaks closely match those in the standard PDF data, further verifying the sample's purity and confirming its correct crystal structure. Notably, the presence of several strong diffraction peaks in the range of 20° to 40° indicates good crystallinity. Furthermore, the absence of extraneous impurity peaks in the XRD pattern confirms the sample's high purity. The diffraction peaks of the synthesized sample fully match those in the standard PDF data, validating the effectiveness and reliability of the synthesis method. Figure 3 The inset shows a photograph of NH4Ga(SO4)2·12H2O crystals. The synthesized crystals exhibit good transparency and regular morphology, consistent with the high crystallinity indicated by the XRD pattern. These results demonstrate that this synthesis method produces high-purity NH4Ga(SO4)2 powder and well-shaped crystals.

[0068] Further, Figure 2 The product NH4Ga(SO4)2 powder obtained in step (3) was heated at 160°C for 30 min. The chemical formula corresponding to this part is:

[0069] .

[0070] Then it was sintered in a quartz boat at 800°C in a vacuum environment for 1 h. The chemical formula corresponding to this part is:

[0071] .

[0072] After grinding, the obtained powder was analyzed by XRD. Figure 4 The XRD pattern of the powder is shown, indicating that the diffraction peaks of the experimental powder are very aligned with the reference pattern in the ICDD / PDF (No.00-41-1013) database. The results show that the synthesized powder has the same crystal structure as standard β-Ga2O3. The main diffraction peaks are located at approximately 2θ values ​​of 18.9°, 30.1°, 35.7°, 37.8°, 43.5°, 57.8° and 63.4°. In addition, the absence of other impurity peaks and the presence of several strong diffraction peaks confirm the high purity and good crystallinity of the sample. This indicates that the precursor can be completely decomposed to form a pure β-Ga2O3 phase.

[0073] Figure 5 (a) and (b) show surface scanning electron microscopy (SEM) images of β-Ga2O3 films that underwent a spin coating and preheating process repeated for five cycles and then annealed at 800°C and 1000°C for one hour. As shown in the SEM images, the surface of the β-Ga2O3 film annealed at 800°C and 1000°C for one hour exhibited a mottled and uneven texture, indicating that five spin coating and preheating cycles were insufficient to form a continuous film. Compared to the film annealed at 800°C, the surface of the film annealed at 1000°C exhibited small holes and spots, as shown in Figure 5. Figure 5 (b) in the figure. This may be due to more intense diffusion and aggregation of material particles occurring at higher temperatures. This may also be accompanied by a certain degree of volatilization or decomposition, causing the film surface to transform from a mottled and uneven structure to a structure with small pores and depressions. After repeating the spin coating and preheating process for 10 cycles, the films annealed at 800°C and 1000°C exhibited relatively continuous and flat surfaces, although some cracks were also observed on the surface of both films. However, the surface of the film annealed at 800°C was smoother, with fewer cracks and finer cracks, as shown in Figure 2. Figure 5 In contrast, the surface of the film annealed at 1000℃ exhibits larger and denser cracks and is rougher, as shown in (c). Figure 5 (d) in Figure 1. The cracking can be attributed to the volatilization of the organic solvent and oxidative decomposition during high-temperature crystallization. High annealing temperatures enhance atomic mobility and laterally expand the atomic nucleus radius, resulting in a slightly roughened film surface. This is likely due to particle recombination caused by increased surface free energy.

[0074] Figure 6Shown are XRD θ-2θ scan patterns of a film grown on a (0001) sapphire substrate, which underwent 10 cycles of spin coating and preheating, followed by annealing at 800°C and 1000°C. The results are in excellent agreement with the corresponding pattern for β-Ga2O3 shown in ICDD-PDF No. 00-41-1103, confirming that the film is composed of β-Ga2O3. In addition to the diffraction peaks of the (0001) sapphire substrate, the XRD pattern exhibits distinct peaks at 18.9°, 38.4°, and 59.2°, corresponding precisely to the (–201), (–402), and (–603) planes of β-Ga2O3, respectively. These characteristic peaks exhibit strong intensity, indicating that the film has a preferential orientation in the [–201] direction. For the film annealed at 1000℃, in addition to the β-Ga2O3 (–201), (–402), and (–603) peaks parallel to the (0001) sapphire plane, there are also diffraction signals from other planes, such as (–401), (–111), (111), and (–313). This indicates the presence of grains from other orientations in the film, resulting in a complex polycrystalline structure. However, for the film annealed at 800℃, except for two small peaks corresponding to the (400) and (002) planes, the peaks from other crystal planes are almost completely absent. The above results indicate that the film is mainly oriented along the (–201) plane of β-Ga2O3, revealing the epitaxial relationship of [–201]β-Ga2O3 / / sapphire corresponding to

[0001] Al2O3. Therefore, it is concluded that the β-Ga2O3 film of the present invention exhibits better crystalline quality than other films.

[0075] Figure 7Panel (a) shows the transmission spectra as a function of wavelength for films prepared on different substrates and subjected to different annealing temperatures. These spectra clearly demonstrate that the films exhibit transmittance exceeding 80% in the 400-800 nm wavelength range. Furthermore, all films exhibit significant absorption in the deep UV spectrum, with a sharp absorption edge observed around 250 nm. After annealing at 800°C and 1000°C for 1 hour, the transmittance of films on quartz substrates is higher than that of films on sapphire substrates. This indicates that the quartz substrate material is more conducive to improving transmittance. Regardless of the substrate used, the transmittance at the lower temperature (800°C) is higher than that at the higher temperature (1000°C). This indicates that the transmittance decreases with increasing annealing temperature. This decrease in transmittance may be due to a deterioration in the material's optical properties or the introduction of greater optical losses at higher temperatures. Combined with the previous SEM analysis results, the lower transmittance observed at higher annealing temperatures may be due to the formation of larger and more dense surface cracks in the films and an increase in their surface roughness. In addition, XRD analysis shows that the films after high-temperature annealing are polycrystalline, while the films after annealing at 800°C have a preferred orientation; this indicates that the films with preferred orientation exhibit better transmittance performance.

[0076] To further analyze the optical properties, the optical band gap was estimated from the transmission spectrum according to the following equation (called Tauc equation): ,

[0077] in, is Planck's constant; is the frequency; is the absorption coefficient; is the proportionality constant, where The power law constant is 1 / 2 in direct conversion and 2 in indirect conversion. In the present invention, assuming direct conversion, the corresponding Tao Ke curve is as follows: Figure 7 As shown in (b) in the figure. Extrapolating a straight line to the horizontal axis gives the optical band gap of the film. Value. Figure 7 As shown in (b) of Figure 1, when using ethylene glycol methyl ether as the solvent, the band gaps of Ga2O3 films grown on quartz substrates annealed at 800°C and 1000°C for 1 hour are approximately 5.52 and 4.4 eV, respectively. In comparison, the band gap of Ga2O3 films grown on sapphire substrates annealed at 800°C for 1 hour is approximately 4.8 eV. When the film is annealed at 1000°C for 1 hour on a sapphire substrate, its band gap is approximately 4.98 eV. This value is consistent with the experimental value of the optical band gap of β-Ga2O3, indicating that sapphire is more suitable than quartz for the production of Ga2O3 films.

[0078] This study uses a simple, low-cost method to fabricate β-Ga2O3 thin films with a preferred [–201] orientation on (0001) sapphire at a relatively low temperature (800°C). The NH4Ga(SO4)2·12H2O prepared during the fabrication process is purified by reaction with an inorganic solution and then separated. This method allows the production of high-quality Ga2O3 films from low-grade gallium metal, thereby reducing overall costs. The crystallinity and surface morphology of the β-Ga2O3 films are significantly affected by the number of spin-coating repetitions and the post-annealing temperature. Notably, β-Ga2O3 films prepared after 10 spin-coating cycles and annealing at 800°C exhibit excellent crystalline quality and a smooth surface. Furthermore, these films exhibit a preferred [–201] orientation and reveal an epitaxial relationship characterized by [–201]β-Ga2O3 / /

[0001] Al2O3. The β-Ga2O3 polycrystalline films are formed at annealing temperatures exceeding 800°C. As the annealing temperature increased from 800°C to 1000°C, the films with smooth surfaces and striped structures gradually transformed into rough crystalline films. All films exhibited high transmittance exceeding 80% for both ultraviolet and visible light with wavelengths exceeding 400 nm. Specifically, Ga2O3 films annealed at 800°C and 1000°C for 1 hour on sapphire substrates exhibited optical band gaps of approximately 4.8 eV and 4.98 eV, respectively. These results indicate that sapphire is a more suitable substrate for growing Ga2O3 films than quartz, suggesting that this simple and efficient inorganic solution reaction method holds great promise for preparing high-quality β-Ga2O3 films.

[0079] The above descriptions are merely several embodiments of the present invention and do not constitute any form of limitation to the present invention. Although the present invention is disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Any technician familiar with the present profession who, without departing from the scope of the technical solution of the present invention, makes slight changes or modifications using the technical contents disclosed above are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a gallium oxide heteroepitaxial thin film, characterized in that: Including: Step 1: Prepare ammonium gallium sulfate hydrate in a molten state; Step 2: Use the ammonium gallium sulfate hydrate in a molten state to prepare a precursor solution; Step 3: Spin-coat the precursor solution onto a sapphire substrate in stages and then anneal it in a vacuum environment to obtain a gallium oxide thin film with a preferred orientation in a preset crystal direction, specifically including: Step 3.1: Spin-coat the precursor solution onto the sapphire substrate in stages; Step 3.2: Repeat Step 3.1 multiple times to obtain a sapphire substrate covered with a gel layer; Step 3.3: Anneal the sapphire substrate covered with the gel layer in a vacuum environment to obtain a gallium oxide thin film with a preferred orientation in a preset crystal direction, the annealing temperature is 800 °C to 900 °C, and the annealing time is 1 h to 1.5 h.

2. The method for preparing a gallium oxide heteroepitaxial thin film according to claim 1, characterized in that: The specific content of Step 3.1 includes: Spin-coat the precursor solution onto the preheated sapphire substrate at a speed of P1 for a continuous spin-coating time of t1 to obtain a first film layer; Spin-coat the precursor solution onto the preheated first film layer at a speed of P2 for a continuous spin-coating time of t2 to obtain a second film layer; Spin-coat the precursor solution onto the preheated second film layer at a speed of P3 for a continuous spin-coating time of t3 to obtain a third film layer; P1 < P2 < P3, and t1 < t2 < t3.

3. The method for preparing a gallium oxide heteroepitaxial thin film according to claim 1, characterized in that: The specific content of Step 3.2 is: Repeat Step 3.1 for 5 to 10 times to obtain a sapphire substrate covered with a gel layer.

4. The method for preparing a gallium oxide heteroepitaxial thin film according to claim 1, characterized in that: The specific content of Step 2 includes: Add an organic solvent and a thickening agent to the ammonium gallium sulfate hydrate in a molten state to prepare a precursor solution.

5. The method for preparing a gallium oxide heteroepitaxial thin film according to claim 4, characterized in that: The organic solvent is ethylene glycol monomethyl ether; the thickening agent is polyacrylamide.

6. The method for preparing a gallium oxide heteroepitaxial thin film according to claim 4, characterized in that: The concentration of the precursor solution is 0.4 mol / L to 0.6 mol / L.

7. The method for preparing a gallium oxide heteroepitaxial thin film according to claim 1, characterized in that: The specific content of Step 1 includes: Step 1.1: Prepare gallium sulfate using gallium metal particles and sulfuric acid; Step 1.2: Prepare ammonium gallium sulfate hydrate crystals using gallium sulfate and ammonium sulfate; Step 1.3: Continuously heat the ammonium gallium sulfate hydrate crystals at a temperature above 60 °C to obtain ammonium gallium sulfate hydrate in a molten state.

8. The method for preparing a gallium oxide heteroepitaxial thin film according to claim 7, characterized in that: In Step 1.2, the molar ratio of gallium sulfate to ammonium sulfate is 1:1 to 1.5.

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