A method for preparing single-domain κ-Ga2O3 epitaxial thin films

Abstract

This invention relates to the field of semiconductor technology, specifically to a method for preparing a single-domain κ-Ga2O3 epitaxial thin film, comprising the following steps: a sapphire substrate is obliquely cut off the m-axis from the C-plane at an angle of 6°~10° to form a stepped substrate; the obliquely cut sapphire substrate is etched using wet etching; after cleaning and nitrogen purging, it is annealed in an oxygen atmosphere to obtain a pretreated sapphire substrate; a coarse single-domain κ-Ga2O3 epitaxial thin film is deposited on the pretreated sapphire substrate using Mist-CVD technology, followed by in-situ annealing in an oxygen atmosphere to obtain the single-domain κ-Ga2O3 epitaxial thin film. In this invention, by limiting the oblique cutting direction and angle on the sapphire substrate surface, κ-Ga2O3 is guided to nucleate in a specific in-plane orientation, fundamentally suppressing the multi-orientation nucleation problem caused by substrate surface symmetry.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and specifically to a method for preparing a single-domain κ-Ga2O3 epitaxial thin film. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Gallium oxide (Ga2O3), an ultrawide bandgap oxide semiconductor, has advantages over third-generation semiconductor materials such as gallium nitride (GaN) and silicon carbide (SiC), including a wider bandgap, higher breakdown field strength, transparent conductivity, the ability to be grown by melt method, and lower cost, making it a research hotspot in the fields of semiconductor materials and devices.

[0004] Ga₂O₃ has five different phase isomers: α, β, γ, δ, and ε(κ). Among these crystal structures, β-Ga₂O₃ has been extensively studied. Furthermore, among the many gallium oxide crystal forms, orthorhombic κ-Ga₂O₃ is the second most stable under ambient temperature and pressure conditions. The advantage of κ-Ga₂O₃ is that it lacks central inversion symmetry along the (001) crystal orientation, exhibiting stronger spontaneous polarization characteristics. Through bandgap trimming and polarization engineering, such as κ-(Al₂O₃)... x Ga 1-x )2O3 / κ-Ga2O3 is expected to induce the formation of high-concentration two-dimensional electron gas (2DEG) at the interface, providing a new material system for the performance of wide-bandgap semiconductor high-temperature, high-frequency, high-power electronic devices and microwave radio frequency devices.

[0005] However, due to the difficulty in obtaining thermodynamically stable bulk κ-Ga₂O₃ single crystals at high temperatures, it can only be heteroepitaxially grown on α-Al₂O₃ and other substrates. Currently, the high symmetry of the substrate in heteroepitaxially grown κ-Ga₂O₃ leads to the existence of in-plane rotating domains within the film. The presence of domain boundaries hinders in-plane electron transport, thus limiting the application of κ-Ga₂O₃. For example, in high-frequency power electronic devices and radio frequency devices, the presence of domain boundaries increases on-resistance, limits frequency response, and exacerbates self-heating effects; in piezoelectric and ferroelectric sensors, the presence of domain boundaries increases signal readout noise and reduces response uniformity and consistency; in ferroelectric memories, the presence of domain boundaries increases write and read leakage current, affecting switching speed and reliability; in solar-blind ultraviolet photodetectors, the presence of domain boundaries increases dark current and reduces response speed. In summary, there is an urgent need to improve the problem of in-plane rotating domains in κ-Ga₂O₃ and explore the growth of single-domain κ-Ga₂O₃, which is crucial for the industrialization of κ-Ga₂O₃. Summary of the Invention

[0006] To overcome the above problems, the present invention provides a method for preparing single-domain κ-Ga2O3 epitaxial thin films.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a single-domain κ-Ga2O3 epitaxial thin film includes the following steps:

[0009] (1) The sapphire substrate is obliquely cut off the m-axis from the C-plane with an angle of 6°~10° to form a stepped substrate;

[0010] (2) The sapphire substrate after beveling is etched by wet etching; after cleaning and nitrogen purging, it is annealed in an oxygen atmosphere to obtain the pretreated sapphire substrate.

[0011] (3) A coarse single-domain κ-Ga2O3 epitaxial film was deposited on a pretreated sapphire substrate by mist chemical vapor deposition (Mist-CVD), and then in-situ annealing was performed in an oxygen atmosphere to obtain a single-domain κ-Ga2O3 epitaxial film.

[0012] In one or more embodiments, in step (2), the etching solution used for wet etching is a mixture of sulfuric acid and hydrogen peroxide solution; the mass fraction of sulfuric acid is 95%~98%, preferably 98%; the mass fraction of hydrogen peroxide is 25%~35%, preferably 30%.

[0013] Preferably, the volume ratio of sulfuric acid to hydrogen peroxide solution is (2.5~3.5):1, more preferably 3:1;

[0014] Preferably, the etching time is 0.5 to 1.5 min, and more preferably 1 min.

[0015] Using a strong oxidizing etching solution to perform short-time chemical etching on sapphire substrates can effectively remove organic contaminants, metallic impurities, and trace amounts of amorphous damage layers that remain on the surface of the sapphire substrates during processing.

[0016] In one or more embodiments, the cleaning method in step (2) includes: ultrasonic cleaning in acetone, ethanol and deionized water in sequence.

[0017] Preferably, the ultrasonic cleaning time is 3 to 8 minutes, and more preferably 5 minutes.

[0018] Stepped ultrasonic cleaning further eliminates various solvent residues. Acetone can remove organic contaminants, ethanol can remove acetone, and deionized water can remove ethanol. Finally, a clean, scratch-free, and dry surface is obtained by purging with high-purity nitrogen.

[0019] Wet etching and stepped ultrasonic cleaning not only ensured the chemical purity of the sapphire substrate surface but also created the necessary conditions for atomic-level reconstruction during subsequent high-temperature annealing. Specifically, wet etching and stepped ultrasonic cleaning thoroughly removed organic contaminants, metallic impurities, and amorphous damage layers from the sapphire substrate surface. If these contaminants were not removed, they would become pinned to the surface during subsequent high-temperature annealing, hindering the free migration of atoms. A thoroughly "purified" surface cleared the way for the regular and orderly rearrangement of surface atoms (i.e., atomic-level reconstruction) under high-temperature conditions, thus creating indispensable conditions.

[0020] In one or more embodiments, in step (2), the annealing temperature is 750~850 ℃, the annealing time is 25~40 min, and the heating rate during annealing is 8~12 ℃ / min.

[0021] High-temperature annealing is a crucial step in achieving single-domain epitaxial growth. In an oxygen atmosphere at 750–850 °C, atoms on the sapphire substrate surface gain sufficient migration energy, undergoing thermodynamic rearrangement to relax into a stable surface structure composed of highly uniform, parallel atomic steps. These atomic steps, exposed along specific crystal orientations, serve as templates for subsequent κ-Ga₂O₃ epitaxial growth, providing optimally energized and uniquely oriented binding sites for initial nucleation. This process fundamentally suppresses the multi-orientation nucleation problem caused by substrate surface symmetry.

[0022] In one or more embodiments, step (3), the method of depositing a coarse single-domain κ-Ga2O3 epitaxial film on a pretreated sapphire substrate by fog chemical vapor deposition, includes:

[0023] The pretreated sapphire substrate was cleaned and purged with nitrogen.

[0024] Gallium acetylacetonate aqueous solution was placed in an ultrasonic atomizer, and the sapphire substrate was fixed in the reactor of the Mist-CVD equipment. The ultrasonic atomizer was turned on, and ultrasonic atomization growth was carried out for 0.5~2 h.

[0025] Preferably, the method for cleaning the pretreated sapphire substrate includes: ultrasonic cleaning in acetone, ethanol and deionized water in sequence.

[0026] More preferably, the time for each ultrasonic cleaning is 3 to 8 minutes, preferably 5 minutes.

[0027] Preferably, the concentration of the gallium acetylacetonate aqueous solution is 0.03~0.08 mol / L, and more preferably 0.05 mol / L.

[0028] More preferably, the method for preparing the gallium acetylacetonate aqueous solution includes: mixing gallium acetylacetonate with deionized water and hydrochloric acid at a volume ratio of (90~110):1.5, and obtaining the gallium acetylacetonate aqueous solution by ultrasonication; wherein the mass fraction of hydrochloric acid is 36%~38%.

[0029] Preferably, the frequency of the ultrasonic atomizer is set to 1.7 or 2.4 MHz, preferably 2.4 MHz.

[0030] Preferably, during the ultrasonic atomization growth process, the temperature of the reactor chamber of the Mist-CVD equipment is 600~700℃, and more preferably 650℃.

[0031] In one or more embodiments, in step (4), the temperature is maintained at 600~700℃, preferably 650℃, during the in-situ annealing process; the in-situ annealing time is 25~40 min, preferably 30 min.

[0032] In-situ annealing is a key post-processing technique for improving the crystal quality and stability of thin films. This process is performed immediately after the growth of coarse single-domain κ-Ga₂O₃ epitaxial films in the same reaction chamber, utilizing an oxygen atmosphere and high temperature to heat-treat the freshly deposited coarse single-domain κ-Ga₂O₃ epitaxial film. Its core function is to induce ordered rearrangement of Ga and O atoms within the film through thermal excitation, effectively filling existing point defects such as O vacancies, while simultaneously eliminating lattice stress accumulated during growth. This process not only significantly improves the crystal integrity of the film and reduces defect density, but also stabilizes the κ phase structure by optimizing the O stoichiometry, suppressing phase transition tendencies, ultimately yielding high-quality single-domain κ-Ga₂O₃ epitaxial films with superior electrical properties and more stable structures.

[0033] The beneficial effects of this invention are as follows:

[0034] This invention relates to the field of semiconductor technology, specifically to a method for preparing a single-domain κ-Ga2O3 epitaxial thin film, comprising the following steps: a sapphire substrate is obliquely cut off the m-axis from the C-plane at an angle of 6°~10° to form a stepped substrate; the obliquely cut sapphire substrate is etched using wet etching; after cleaning and nitrogen purging, it is annealed in an oxygen atmosphere to obtain a pretreated sapphire substrate; a coarse single-domain κ-Ga2O3 epitaxial thin film is deposited on the pretreated sapphire substrate using Mist-CVD technology, followed by in-situ annealing in an oxygen atmosphere to obtain the single-domain κ-Ga2O3 epitaxial thin film. In this invention, by limiting the oblique cutting direction and angle on the sapphire substrate surface, κ-Ga2O3 is guided to nucleate in a specific in-plane orientation, fundamentally suppressing the multi-orientation nucleation problem caused by substrate surface symmetry. Specifically, a flat C-plane sapphire substrate is beveled to form a stepped substrate composed of numerous atomic-level steps. Due to the higher coordination number and lower nucleation barrier at the corners of the atomic-level steps, Ga and O atoms preferentially nucleate at these locations. More importantly, the beveling off the m-axis allows the crystal lattice of the nucleus to match the atomic structure of the step edges, achieving the lowest energy state and guiding κ-Ga2O3 to nucleate in a specific in-plane orientation. Furthermore, when the beveling angle off the m-axis is small, the number of steps is small, the step horizontal plane is wide, and the atomic diffusion ability is weak, resulting in Ga and O atoms nucleating on the step horizontal plane and randomly oriented. However, when the beveling angle off the m-axis increases to 6°~10°, the number of steps is large, the step horizontal plane is narrow, and even though the atomic diffusion ability is weak, the diffusion distance to the step edge is short, making it easy for the atoms to be "captured" by the steps and nucleate in a specific in-plane orientation. Subsequently, the nucleus grows one-dimensionally along the step edge direction to form a "nucleus chain," and based on this "nucleus chain," it grows two-dimensionally laterally along the step direction to form a plane. This "point-to-line-to-surface" growth pattern effectively maintains the in-plane orientation of the initial κ-Ga2O3 nuclei, thus yielding single-domain κ-Ga2O3 epitaxial films. Attached Figure Description

[0035] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0036] Figure 1 The images are X-ray diffraction (XRD) φ scan images of the single-domain κ-Ga2O3 epitaxial films prepared in Examples 1 to 3.

[0037] Figure 2 X-ray diffraction (XRD) φ scan images of the epitaxial thin films prepared in Comparative Examples 1 to 9;

[0038] Figure 3To guide the crystal orientation of the κ-Ga2O3 epitaxial film when the C-plane of a sapphire substrate is obliquely cut off from the m-axis at an angle of 6°; (a) is a three-dimensional schematic diagram of the sapphire substrate when the C-plane is obliquely cut off from the m-axis at an angle of 6°; (b) is a cross-sectional schematic diagram of the stepped steps in (a); (c) is a schematic diagram of the O atom arrangement on the horizontal plane of the stepped steps in (a); (d) is the crystal structure of κ-Ga2O3; and (e) is a schematic diagram of the possible O atom arrangement of the κ-Ga2O3 film grown in (a).

[0039] Figure 4 To guide the crystal orientation of the κ-Ga2O3 epitaxial film when the C-plane of the sapphire substrate is obliquely cut off from the a-axis at an angle of 6°; (a) is a three-dimensional schematic diagram of the sapphire substrate when the C-plane is obliquely cut off from the a-axis at an angle of 6°; (b) is a cross-sectional schematic diagram of the stepped steps in (a); (c) is a schematic diagram of the O atom arrangement on the horizontal plane of the stepped steps in (a); (d) and (e) are schematic diagrams of two possible O atom arrangements of the κ-Ga2O3 film grown in (a). Detailed Implementation

[0040] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0041] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0042] Among the various gallium oxide crystal forms, orthorhombic κ-Ga₂O₃ is the second most stable under ambient temperature and pressure conditions. The advantage of κ-Ga₂O₃ is that it lacks central inversion symmetry along the (001) crystal orientation, exhibiting stronger spontaneous polarization characteristics. Through bandgap trimming and polarization engineering, such as κ-(Al₂O₃) x Ga 1-x )2O3 / κ-Ga2O3 is expected to induce the formation of high-concentration two-dimensional electron gas (2DEG) at the interface, providing a new material system for the performance of wide-bandgap semiconductor high-temperature, high-frequency, high-power electronic devices and microwave radio frequency devices.

[0043] However, due to the difficulty in obtaining thermodynamically stable bulk κ-Ga₂O₃ single crystals at high temperatures, it can only be heteroepitaxially grown on α-Al₂O₃ and other substrates. Currently, the high symmetry of the substrate in heteroepitaxially grown κ-Ga₂O₃ leads to the existence of in-plane rotating domains within the film. The presence of domain boundaries hinders in-plane electron transport, thus limiting the application of κ-Ga₂O₃. For example, in high-frequency power electronic devices and radio frequency devices, the presence of domain boundaries increases on-resistance, limits frequency response, and exacerbates self-heating effects; in piezoelectric and ferroelectric sensors, the presence of domain boundaries increases signal readout noise and reduces response uniformity and consistency; in ferroelectric memories, the presence of domain boundaries increases write and read leakage current, affecting switching speed and reliability; in solar-blind ultraviolet photodetectors, the presence of domain boundaries increases dark current and reduces response speed. In summary, there is an urgent need to improve the problem of in-plane rotating domains in κ-Ga₂O₃ and explore the growth of single-domain κ-Ga₂O₃, which is crucial for the industrialization of κ-Ga₂O₃.

[0044] This invention relates to the field of semiconductor technology, specifically to a method for preparing a single-domain κ-Ga2O3 epitaxial thin film, comprising the following steps: a sapphire substrate is obliquely cut off the m-axis from the C-plane at an angle of 6°~10° to form a stepped substrate; the obliquely cut sapphire substrate is etched using a wet etching method; after cleaning and nitrogen purging, it is annealed in an oxygen atmosphere to obtain a pretreated sapphire substrate; a coarse single-domain κ-Ga2O3 epitaxial thin film is deposited on the pretreated sapphire substrate using Mist-CVD technology, followed by in-situ annealing in an oxygen atmosphere to obtain the single-domain κ-Ga2O3 epitaxial thin film.

[0045] In this invention, by limiting the oblique cutting direction and oblique cutting angle of the sapphire substrate surface, κ-Ga2O3 is guided to nucleate in a specific in-plane orientation, which fundamentally suppresses the multi-orientation nucleation problem caused by the symmetry of the substrate surface. Specifically, a flat C-plane sapphire substrate is beveled to form a stepped substrate composed of numerous atomic-level steps. Due to the higher coordination number and lower nucleation barrier at the corners of the atomic-level steps, Ga and O atoms preferentially nucleate at these locations. More importantly, the beveling off the m-axis allows the crystal lattice of the nucleus to match the atomic structure of the step edges, achieving the lowest energy state and guiding κ-Ga2O3 to nucleate in a specific in-plane orientation. Furthermore, when the beveling angle off the m-axis is small, the number of steps is small, the step horizontal plane is wide, and the atomic diffusion ability is weak, resulting in Ga and O atoms nucleating on the step horizontal plane and randomly oriented. However, when the beveling angle off the m-axis increases to 6°~10°, the number of steps is large, the step horizontal plane is narrow, and even though the atomic diffusion ability is weak, the diffusion distance to the step edge is short, making it easy for the atoms to be "captured" by the steps and nucleate in a specific in-plane orientation. Subsequently, the nucleus grows one-dimensionally along the step edge direction to form a "nucleus chain," and based on this "nucleus chain," it grows two-dimensionally laterally along the step direction to form a plane. This "point-to-line-to-surface" growth pattern effectively maintains the in-plane orientation of the initial κ-Ga2O3 nuclei, thus yielding single-domain κ-Ga2O3 epitaxial films.

[0046] Furthermore, high-temperature annealing is a crucial step in achieving single-domain epitaxial growth. In an oxygen atmosphere at 750–850 °C, atoms on the sapphire substrate surface gain sufficient migration energy, undergoing thermodynamic rearrangement to relax into a stable surface structure composed of highly uniform, parallel atomic steps. These atomic steps exposed along specific crystal orientations serve as templates for subsequent κ-Ga2O3 epitaxial growth, providing optimally energized and uniquely oriented binding sites for initial nucleation. This process fundamentally suppresses the multi-orientation nucleation problem caused by substrate surface symmetry.

[0047] In-situ annealing is a key post-processing technique for improving the crystal quality and stability of thin films. This process is performed immediately after the growth of coarse single-domain κ-Ga₂O₃ epitaxial films in the same reaction chamber, utilizing an oxygen atmosphere and high temperature to heat-treat the freshly deposited coarse single-domain κ-Ga₂O₃ epitaxial film. Its core function is to induce ordered rearrangement of Ga and O atoms within the film through thermal excitation, effectively filling existing point defects such as O vacancies, while simultaneously eliminating lattice stress accumulated during growth. This process not only significantly improves the crystal integrity of the film and reduces defect density, but also stabilizes the κ phase structure by optimizing the O stoichiometry, suppressing phase transition tendencies, ultimately yielding high-quality single-domain κ-Ga₂O₃ epitaxial films with superior electrical properties and more stable structures.

[0048] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0049] The following examples and comparative examples illustrate the preparation methods for the 0.05 mol / L aqueous solution of acetyl gallium:

[0050] Dissolve an appropriate amount of gallium acetylacetonate solid powder in deionized water and stir until dissolved. Based on the volume of deionized water, add 1.5% (36.5% by mass) of concentrated hydrochloric acid to the gallium acetylacetonate aqueous solution to increase the dissolution of gallium acetylacetonate. Use an ultrasonic device to sonicate the solution until gallium acetylacetonate is completely dissolved.

[0051] Example 1

[0052] Preparation of single-domain κ-Ga2O3 epitaxial thin films:

[0053] (1) The sapphire substrate is obliquely cut off the m axis of the C plane with an angle of 6° to form a stepped substrate.

[0054] (2) An etching solution was obtained by mixing 98% concentrated sulfuric acid and 30% hydrogen peroxide at a volume ratio of 3:1. The sapphire substrate cut in step (1) was placed in the etching solution and chemically etched for 1 min. The etched substrate was then removed and rinsed with flowing deionized water to remove the residual etching solution. The substrate was then ultrasonically cleaned in acetone, ethanol and deionized water for 5 min in sequence, and then its surface was purged with high-purity N2. Subsequently, the substrate was placed in a tube annealing furnace for annealing at a heating rate of 10 ℃ / min, a temperature of 800 ℃, an oxygen atmosphere and a time of 30 min to obtain the pretreated sapphire substrate.

[0055] (3) The pretreated sapphire substrate was ultrasonically cleaned in acetone, ethanol and deionized water for 5 min in sequence, and then its surface was purged with high-purity N2. After that, it was fixed on the sample stage of the reaction chamber of the Mist-CVD equipment. The prepared 0.05 mol / L acetyl gallium aqueous solution was placed in the ultrasonic nebulizer (frequency of 2.4 MHz), and argon gas (flow rate of 5000 mL / min) was used as the carrier gas to transport the atomized droplets to the reaction chamber for reaction. Before turning on the ultrasonic nebulizer, the reaction chamber was heated to 650 ℃ and kept at that temperature for 15 min. The reaction chamber temperature was then maintained at 650 ℃ for ultrasonic atomization growth for 1 h.

[0056] (4) After ultrasonic atomization growth is completed, turn off the ultrasonic atomizer, stop atomization, and stop the supply of argon gas; maintain the reaction chamber temperature at 650 ℃, use oxygen (flow rate of 1000 mL / min) as the annealing atmosphere, and control the annealing time at 30 min. After the in-situ annealing is completed and the equipment is cooled to room temperature, remove the substrate to obtain a single-domain κ-Ga2O3 epitaxial film.

[0057] Example 2

[0058] (1) The sapphire substrate is obliquely cut off the m axis of the C plane with an angle of 8° to form a stepped substrate.

[0059] (2) A sapphire substrate with a mass fraction of 98% sulfuric acid and a mass fraction of 30% hydrogen peroxide were mixed at a volume ratio of 3:1 to obtain an etching solution. The sapphire substrate cut in step (1) was placed in the etching solution and chemically etched for 1 min. The etched substrate was then removed and rinsed with flowing deionized water to remove the residual etching solution. The substrate was then ultrasonically cleaned in acetone, ethanol and deionized water for 5 min in sequence, and then its surface was purged with high-purity N2. Subsequently, the substrate was placed in a tube annealing furnace for annealing at a heating rate of 8 ℃ / min, a temperature of 750 ℃, an oxygen atmosphere and a time of 40 min to obtain a pretreated sapphire substrate.

[0060] (3) The pretreated sapphire substrate was ultrasonically cleaned in acetone, ethanol and deionized water for 5 min in sequence, and then its surface was purged with high-purity N2. After that, it was fixed on the sample stage of the reaction chamber of the Mist-CVD equipment. The prepared 0.05 mol / L acetyl gallium aqueous solution was placed in the ultrasonic nebulizer (frequency of 2.4 MHz), and argon gas (flow rate of 5000 mL / min) was used as the carrier gas to transport the atomized droplets to the reaction chamber for reaction. Before turning on the ultrasonic nebulizer, the reaction chamber was heated to 650 ℃ and kept at that temperature for 15 min. The reaction chamber temperature was then maintained at 650 ℃ for ultrasonic atomization growth for 1 h.

[0061] (4) After ultrasonic atomization growth is completed, turn off the ultrasonic atomizer, stop atomization, and stop the supply of argon gas; maintain the reaction chamber temperature at 650 ℃, use oxygen (flow rate of 1000 mL / min) as the annealing atmosphere, and control the annealing time at 30 min. After the in-situ annealing is completed and the equipment is cooled to room temperature, remove the substrate to obtain a single-domain κ-Ga2O3 epitaxial film.

[0062] Example 3

[0063] (1) The sapphire substrate is obliquely cut off the m axis of the C plane with an angle of 10° to form a stepped substrate.

[0064] (2) A sapphire substrate with a mass fraction of 98% sulfuric acid and a mass fraction of 30% hydrogen peroxide were mixed at a volume ratio of 3:1 to obtain an etching solution. The sapphire substrate cut in step (1) was placed in the etching solution and chemically etched for 1 min. The etched substrate was then removed and rinsed with flowing deionized water to remove the residual etching solution. The substrate was then ultrasonically cleaned in acetone, ethanol and deionized water for 5 min in sequence, and then its surface was purged with high-purity N2. Subsequently, the substrate was placed in a tube annealing furnace for annealing at a heating rate of 12 ℃ / min, a temperature of 850 ℃, an oxygen atmosphere and a time of 25 min to obtain a pretreated sapphire substrate.

[0065] (3) The pretreated sapphire substrate was ultrasonically cleaned in acetone, ethanol and deionized water for 5 min in sequence, and then its surface was purged with high-purity N2. After that, it was fixed on the sample stage of the reaction chamber of the Mist-CVD equipment. The prepared 0.05 mol / L acetyl gallium aqueous solution was placed in the ultrasonic nebulizer (frequency of 2.4 MHz), and argon gas (flow rate of 5000 mL / min) was used as the carrier gas to transport the atomized droplets to the reaction chamber for reaction. Before turning on the ultrasonic nebulizer, the reaction chamber was heated to 650 ℃ and kept at that temperature for 15 min. The reaction chamber temperature was then maintained at 650 ℃ for ultrasonic atomization growth for 1 h.

[0066] (4) After ultrasonic atomization growth is completed, turn off the ultrasonic atomizer, stop atomization, and stop the supply of argon gas; maintain the reaction chamber temperature at 650 ℃, use oxygen (flow rate of 1000 mL / min) as the annealing atmosphere, and control the annealing time at 30 min. After the in-situ annealing is completed and the equipment is cooled to room temperature, remove the substrate to obtain a single-domain κ-Ga2O3 epitaxial film.

[0067] Comparative Example 1

[0068] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the C-plane from the m-axis at an angle of 0.5° to form a stepped substrate.

[0069] The other methods are the same as in Example 1.

[0070] Comparative Example 2

[0071] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the m-axis of the C-plane with an angle of 1° to form a stepped substrate.

[0072] The other methods are the same as in Example 1.

[0073] Comparative Example 3

[0074] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the m-axis of the C-plane with an angle of 2° to form a stepped substrate.

[0075] The other methods are the same as in Example 1.

[0076] Comparative Example 4

[0077] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the m-axis of the C-plane with an angle of 4° to form a stepped substrate.

[0078] The other methods are the same as in Example 1.

[0079] Comparative Example 5

[0080] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the C-plane from the a-axis at an angle of 0.4° to form a stepped substrate.

[0081] The other methods are the same as in Example 1.

[0082] Comparative Example 6

[0083] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the C-plane from the a-axis at an angle of 1° to form a stepped substrate.

[0084] The other methods are the same as in Example 1.

[0085] Comparative Example 7

[0086] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the C-plane from the a-axis at an angle of 2° to form a stepped substrate.

[0087] The other methods are the same as in Example 1.

[0088] Comparative Example 8

[0089] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the C-plane from the a-axis at an angle of 4° to form a stepped substrate.

[0090] The other methods are the same as in Example 1.

[0091] Compared with Example 1, in step (1), the sapphire substrate is obliquely cut off the C-plane from the a-axis at an angle of 6° to form a stepped substrate.

[0092] The other methods are the same as in Example 1.

[0093] The epitaxial films prepared in Examples 1 to 3 and Comparative Examples 1 to 9 were characterized:

[0094] Figure 1 These are X-ray diffraction (XRD) φ-scan images of the single-domain κ-Ga2O3 epitaxial films prepared in Examples 1-3. Figure 1 As can be seen from the examples 1 to 3, the number of diffraction peaks of the κ-Ga2O3{122} crystal plane family in the κ-Ga2O3 epitaxial films prepared in Examples 1 to 3 is only 4. Therefore, the κ-Ga2O3 epitaxial films prepared in Examples 1 to 3 are single domains.

[0095] Figure 2 The images are X-ray diffraction (XRD) φ-scan images of the epitaxial thin films prepared in Comparative Examples 1 to 9. Figure 2 As can be seen from the data, the number of diffraction peaks of the κ-Ga2O3{122} crystal plane family in the κ-Ga2O3 epitaxial films prepared in Comparative Examples 1 to 9 is 8 or 12. Therefore, the κ-Ga2O3 epitaxial films prepared in Comparative Examples 1 to 9 are not single domains.

[0096] Figure 1 and Figure 2 The X-ray diffraction (XRD) φ scan curve is a ring curve, so the peaks at rotation angles of 0° and 360° are the same.

[0097] Figure 3 To guide the crystal orientation of the κ-Ga2O3 epitaxial film when the C-plane of a sapphire substrate is obliquely cut off from the m-axis at an angle of 6°; (a) is a three-dimensional schematic diagram of the sapphire substrate when the C-plane is obliquely cut off from the m-axis at an angle of 6°; (b) is a cross-sectional schematic diagram of the stepped steps in (a); (c) is a schematic diagram of the O atom arrangement on the horizontal plane of the stepped steps in (a); (d) is the crystal structure of κ-Ga2O3; and (e) is a schematic diagram of the possible O atom arrangement of the κ-Ga2O3 film grown in (a).

[0098] Figure 4 To guide the crystal orientation of the κ-Ga2O3 epitaxial film when the C-plane of the sapphire substrate is obliquely cut off from the a-axis at an angle of 6°; (a) is a three-dimensional schematic diagram of the sapphire substrate when the C-plane is obliquely cut off from the a-axis at an angle of 6°; (b) is a cross-sectional schematic diagram of the stepped steps in (a); (c) is a schematic diagram of the O atom arrangement on the horizontal plane of the stepped steps in (a); (d) and (e) are schematic diagrams of two possible O atom arrangements of the κ-Ga2O3 film grown in (a).

[0099] In this invention, by limiting the oblique cutting direction and oblique cutting angle of the sapphire substrate surface, κ-Ga2O3 is guided to nucleate in a specific in-plane orientation, which fundamentally suppresses the multi-orientation nucleation problem caused by the symmetry of the substrate surface. Specifically, a flat C-plane sapphire substrate is beveled to form a stepped substrate composed of numerous atomic-level steps. Due to the higher coordination number and lower nucleation barrier at the corners of the atomic-level steps, Ga and O atoms preferentially nucleate at these locations. More importantly, the beveling off the m-axis allows the crystal lattice of the nucleus to match the atomic structure of the step edges, achieving the lowest energy state and guiding κ-Ga2O3 to nucleate in a specific in-plane orientation. Furthermore, when the beveling angle off the m-axis is small, the number of steps is small, the step horizontal plane is wide, and the atomic diffusion ability is weak, resulting in Ga and O atoms nucleating on the step horizontal plane and randomly oriented. However, when the beveling angle off the m-axis increases to 6°~10°, the number of steps is large, the step horizontal plane is narrow, and even though the atomic diffusion ability is weak, the diffusion distance to the step edge is short, making it easy for the atoms to be "captured" by the steps and nucleate in a specific in-plane orientation. Subsequently, the nucleus grows one-dimensionally along the step edge direction to form a "nucleus chain," and based on this "nucleus chain," it grows two-dimensionally laterally along the step direction to form a plane. This "point-to-line-to-surface" growth pattern effectively maintains the in-plane orientation of the initial κ-Ga2O3 nuclei, thus yielding single-domain κ-Ga2O3 epitaxial films.

[0100] The in-plane orientation of the initial κ-Ga₂O₃ nucleus depends on the oblique cutting direction, i.e., oblique cutting along the m-axis or along the a-axis. If oblique cutting along the m-axis, it will form as shown in the diagram. Figure 3 The orientation shown in (e) is a single plane orientation; if it is obliquely cut along the a-axis, then it will form as shown in (e). Figure 4 The images (d) and (e) show a dual (not single) in-plane orientation. Therefore, single-domain κ-Ga2O3 epitaxial films cannot be prepared on substrates with the C plane obliquely cut off from the a-axis.

[0101] Furthermore, if the off-m-axis skew angle is increased further, it is theoretically possible to prepare single-domain κ-Ga2O3 epitaxial films. However, increasing the skew angle further will lead to excessively high step density, increasing the surface roughness of the film, and will also increase production costs. Therefore, the off-m-axis skew angle is limited to 6°~10°.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a single-domain κ-Ga2O3 epitaxial thin film, characterized by, Comprise the following steps: (1) C face bias m-axis beveling is carried out to sapphire substrate, and the angle of beveling is 6°~10°, to form stepped terrace substrate;κ-Ga2O3 is guided to nucleate in a specific in-plane orientation by limiting the beveling direction and beveling angle of the surface of sapphire substrate; (2) Etching treatment is carried out to the beveled sapphire substrate in a wet etching manner;After cleaning and nitrogen blowing, annealing treatment is carried out in an oxygen atmosphere to obtain a pretreated sapphire substrate; (3) Coarse single-domain κ-Ga2O3 epitaxial film is deposited on the pretreated sapphire substrate by a mist chemical vapor deposition method, and then single-domain κ-Ga2O3 epitaxial film is obtained by in-situ annealing in an oxygen atmosphere; In step (2), the etching solution used in wet etching is a mixture of sulfuric acid and hydrogen peroxide solution; In step (2), the temperature of annealing treatment is 750~850 ℃, the time of annealing treatment is 25~40 min, and the heating rate during annealing treatment is 8~12 ℃ / min.

2. The production method according to claim 1, wherein The mass fraction of sulfuric acid is 95%~98%, and the mass fraction of hydrogen peroxide is 25%~35%; The volume ratio of sulfuric acid to hydrogen peroxide solution is (2.5~3.5):1; The etching time is 0.5~1.5 min.

3. The production method according to claim 1, wherein In step (2), the cleaning method comprises: sequentially placing in acetone, ethanol and deionized water for ultrasonic cleaning;Each time of ultrasonic cleaning lasts for 3~8 min.

4. The production method according to claim 1, wherein In step (3), the method of depositing coarse single-domain κ-Ga2O3 epitaxial film on the pretreated sapphire substrate by a mist chemical vapor deposition method comprises: The pretreated sapphire substrate is cleaned and nitrogen blown; The gallium acetylacetonate aqueous solution is placed in an ultrasonic atomizer, the sapphire substrate is fixed in a Mist-CVD equipment reactor, the ultrasonic atomizer is started, and ultrasonic atomization growth is carried out for 0.5~2 h.

5. The production method according to claim 4, wherein The method of cleaning the pretreated sapphire substrate comprises: sequentially placing in acetone, ethanol and deionized water for ultrasonic cleaning;Each time of ultrasonic cleaning lasts for 3~8 min.

6. The production method according to claim 4, wherein The concentration of the gallium acetylacetonate aqueous solution is 0.03~0.08 mol / L.

7. The production method according to claim 4, wherein The frequency of the ultrasonic atomizer is set to 1.7 or 2.4 MHz.

8. The production method according to claim 4, wherein The temperature of the Mist-CVD equipment reactor cavity during ultrasonic atomization growth is 600~700 ℃.

9. The production method according to claim 1, wherein The temperature is maintained at 600~700 ℃ during in-situ annealing;The time of in-situ annealing is 25~40 min.

Images