ZnGa2O4 epitaxial film with high crystallinity and high conductivity and preparation method thereof

Abstract

The invention relates to the technical field of semiconductor materials, in particular to a high-crystallinity and high-conductivity ZnGa2O4 epitaxial thin film and a preparation method thereof. Mixing the gallium acetylacetonate aqueous solution, the zinc acetylacetonate aqueous solution and the tetravalent tin salt aqueous solution to form a precursor solution; cleaning and nitrogen purging a sapphire substrate, fixing the sapphire substrate in a fog chemical vapor deposition equipment reactor, putting the precursor solution into an ultrasonic atomizer, starting the ultrasonic atomizer, and performing ultrasonic atomization growth to obtain a coarse ZnGa2O4 epitaxial film; and then performing in-situ annealing to obtain the ZnGa2O4 epitaxial thin film with high crystallinity and high conductivity. The crystallinity and conductivity of the ZnGa2O4 epitaxial thin film are synergistically improved through doping of a proper amount of tin and in-situ annealing.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials technology, specifically to a highly crystalline and highly conductive ZnGa2O4 epitaxial thin film and its preparation method. 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] In recent years, wide-bandgap semiconductor materials such as gallium oxide (Ga2O3), gallium nitride (GaN), silicon carbide (SiC), and zinc oxide (ZnO) have been widely used in power electronics, semiconductor lighting, ultraviolet detection, and radio frequency microwave devices due to their stability under high pressure and high temperature environments, high efficiency, high energy conversion rate, and low susceptibility to radiation interference. Among them, the ternary alloy ZnGa2O4, as a direct bandgap semiconductor material, has a high bandgap of 5.2 eV, excellent chemical stability, strong radiation resistance, and a unique dual-cation structure. Moreover, compared with elemental semiconductors such as diamond or binary oxide semiconductors such as Ga2O3 and ZnO, it can achieve controllable electrical properties without doping. In addition, compared with ternary alloy semiconductors, it has a stable crystal phase.

[0004] ZnGa₂O₄ has the space group Fd⁻³m and a lattice constant of 8.33 Å. It exhibits both normal and anti-spinel structures. In the normal spinel, Zn 2+ Occupying one-eighth of the tetrahedral sites, Ga 3+ Occupying half of the octahedral sites; in anti-spinel, Zn 2+ With half of the total Ga 3+ Occupying octahedral sites, leaving half of the total Ga 3+ Occupying tetrahedral sites, ZnGa2O4 has long played a crucial role as a fluorescent material in photoluminescence and electroluminescence. When bombarded with a 245-254 nm ultraviolet laser or electron beam, ZnGa2O4 emits blue light; when doped with transition metals or rare earth elements, it emits red, yellow, and green light. Compared to bulk powders, ZnGa2O4 epitaxial films have attracted more attention due to their superior thermal stability, lower outgassing, and longer device lifetime.

[0005] However, due to lattice and thermal mismatches between ZnGa2O4 and the substrate during heteroepitaxial growth, numerous defects, such as grain boundaries and dislocations, exist within the ZnGa2O4 epitaxial film, resulting in poor crystal quality. Furthermore, as a wide-bandgap semiconductor, ZnGa2O4 is nearly insulating due to the negligible number of intrinsic free electrons generated by thermal excitation. Although oxygen vacancies introduce donor levels in the bandgap, the effective free electron concentration they provide is extremely low, preventing the achievement of high conductivity. These poor crystal quality and low conductivity hinder the application of ZnGa2O4 epitaxial films in transparent conductive electrodes, light-emitting devices, and epitaxial thin-film transistors. Summary of the Invention

[0006] To overcome the above problems, the present invention provides a ZnGa2O4 epitaxial thin film with high crystallinity and high conductivity and a method for preparing the same.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a highly crystalline and highly conductive ZnGa2O4 epitaxial thin film, comprising the following steps: (1) A precursor solution is formed by mixing an aqueous solution of gallium acetylacetonate, an aqueous solution of zinc acetylacetonate, and an aqueous solution of tetravalent tin salt; (2) After cleaning and purging with nitrogen, the sapphire substrate is fixed in the reactor of the Mist-CVD equipment. The precursor solution is placed in the ultrasonic atomizer, the ultrasonic atomizer is turned on, and the crude ZnGa2O4 epitaxial film is obtained by ultrasonic atomization growth. Then, in-situ annealing is performed to obtain a ZnGa2O4 epitaxial film with high crystallinity and high conductivity.

[0008] In one or more embodiments, in step (1), the concentration of the gallium acetylacetonate aqueous solution is 0.03~0.08 mol / L, preferably 0.05 mol / L.

[0009] In one or more embodiments, in step (1), 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 after sonication; wherein the mass fraction of hydrochloric acid is 36%~38%.

[0010] In one or more embodiments, in step (1), the concentration of the zinc acetylacetonate aqueous solution is 0.03~0.08 mol / L, preferably 0.05 mol / L.

[0011] In one or more embodiments, the method for preparing the zinc acetylacetonate aqueous solution in step (1) includes: mixing zinc acetylacetonate with deionized water and hydrochloric acid at a volume ratio of (90~110):1.5, and obtaining the zinc acetylacetonate aqueous solution after sonication; wherein the mass fraction of hydrochloric acid is 36%~38%.

[0012] In one or more embodiments, in step (1), the tetravalent tin salt is selected from tin tetrachloride, tin sulfate and tin bromide, preferably tin tetrachloride.

[0013] In one or more embodiments, in step (1), the concentration of the tetravalent tin salt aqueous solution is 0.03~0.08 mol / L, preferably 0.05 mol / L.

[0014] In one or more embodiments, in step (1), the method for preparing the tetravalent tin salt aqueous solution includes: mixing the tetravalent tin salt with deionized water and hydrochloric acid at a volume ratio of (90~110):20, and obtaining the tetravalent tin salt aqueous solution after sonication; wherein the mass fraction of hydrochloric acid is 36%~38%.

[0015] In one or more embodiments, in step (1), the volume ratio of the gallium acetylacetonate aqueous solution, the zinc acetylacetonate aqueous solution, and the tetravalent tin salt aqueous solution is (46~49.5):50:(4~0.5), preferably (46~48):50:(4~2), and more preferably 48:50:2.

[0016] In one or more embodiments, the method for cleaning the sapphire substrate in step (2) includes: ultrasonically cleaning the sapphire substrate 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 eliminates various solvent residues. Acetone removes organic contaminants, ethanol removes acetone, and deionized water removes ethanol. Finally, high-purity nitrogen purging yields a clean, scratch-free, and dry surface.

[0019] In one or more embodiments, in step (2), the frequency of the ultrasonic atomizer is 1.7~2.4 MHz, preferably 2.4 MHz.

[0020] In one or more embodiments, in step (2), the temperature of the reactor cavity of the Mist-CVD equipment is 700~750 ℃ ​​during the ultrasonic atomization growth process, preferably 750 ℃; the ultrasonic atomization growth time is 1~2 h, preferably 1 h.

[0021] In one or more embodiments, in step (2), argon is used as a carrier gas to transport the atomized droplets to the reactor chamber of the Mist-CVD equipment for reaction.

[0022] In one or more embodiments, in step (2), the in-situ annealing method includes: after stopping atomization, continuing to introduce argon gas as an annealing atmosphere, maintaining the temperature at 700~750 ℃, preferably 750 ℃; and the in-situ annealing time is 20~40 min, preferably 30 min.

[0023] In a second aspect, the present invention provides a highly crystalline and highly conductive ZnGa2O4 epitaxial thin film, which is prepared by the preparation method described in the first aspect.

[0024] In one or more embodiments, the highly crystalline and highly conductive ZnGa2O4 epitaxial film is doped with tin, and the tin doping concentration is 0.5~4 at%, preferably 2 at%.

[0025] The beneficial effects of this invention are as follows: In this invention, the crystallinity and conductivity of ZnGa2O4 epitaxial films are synergistically improved by doping with an appropriate amount of tin and in-situ annealing. Specifically, the tin element is mainly Sn. 4+ Tin doping introduces ions into the ZnGa2O4 lattice, optimizing the crystal structure through substitutional doping. Regarding crystal quality, tin doping can adjust lattice parameters, reducing lattice mismatch between the epitaxial film and the C-plane sapphire substrate, thereby reducing stress and defect density during epitaxial growth and promoting more uniform and dense crystal growth. However, the concentration of tin doping must be controlled within the solid solubility limit; excessive doping leads to the precipitation of SnO2 impurity phases, damaging crystal integrity and hindering the improvement of crystal quality. Regarding conductivity, Sn… 4+ As an n-type dopant, ions replace Ga in ZnGa₂O₄ 3+When tin is applied to sites, additional free electrons are introduced, effectively increasing the carrier concentration and thus significantly improving the conductivity of the epitaxial film. However, excessive tin doping is not conducive to improving conductivity, and the sharp increase in ionized impurity scattering severely restricts the carrier migration ability. After ultrasonic atomization growth, in-situ annealing provides sufficient energy for the atoms inside the epitaxial film to migrate and rearrange. This adjustment of the atomic-level structure can effectively repair point defects and lattice distortions generated during rapid deposition, promote grain growth and grain boundary optimization, thereby reducing the crystal defect density and making the crystal structure of the epitaxial film more complete and ordered, significantly improving the crystal quality. At the same time, in the oxygen-deficient argon annealing atmosphere, oxygen atoms on the surface of the epitaxial film are more likely to detach from the lattice, thereby generating a certain concentration of oxygen vacancies inside the material. These oxygen vacancies can effectively act as n-type doping centers in ZnGa2O4, contributing free electrons and significantly increasing the carrier concentration. The increase in carrier concentration directly leads to the enhancement of the conductivity of the epitaxial film, which complements the effect of tin doping introducing additional carriers, synergistically achieving a leap in the conductivity of the epitaxial film by orders of magnitude. Attached Figure Description

[0026] 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.

[0027] Figure 1 X-ray diffraction (XRD) θ-2θ scan images of the highly crystalline and highly conductive ZnGa2O4 epitaxial films prepared in Examples 1-2 and Comparative Examples 1-3. Figure 2 The current (I)-voltage (V) curves of the highly crystalline and highly conductive ZnGa2O4 epitaxial films prepared in Examples 1 and 2, and the ZnGa2O4 epitaxial films prepared in Comparative Examples 1 and 3 are shown. Detailed Implementation

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The method for preparing a 0.05 mol / L aqueous solution of gallium acetylacetonate is as follows: Disperse an appropriate amount of gallium acetylacetonate solid powder in deionized water and stir to dissolve it. Based on the volume of deionized water, add 1.5% of concentrated hydrochloric acid (36.5% by mass) to the gallium acetylacetonate aqueous solution. Concentrated hydrochloric acid can increase the dissolution of gallium acetylacetonate. Perform ultrasonic treatment until gallium acetylacetonate is completely dissolved.

[0032] The method for preparing a 0.05 mol / L zinc acetylacetone aqueous solution is as follows: Disperse an appropriate amount of zinc acetylacetonate solid powder in deionized water and stir to dissolve it. Based on the volume of deionized water, add 1.5% of 36.5% concentrated hydrochloric acid to the zinc acetylacetonate aqueous solution. Concentrated hydrochloric acid can increase the dissolution of zinc acetylacetonate. Perform ultrasonic treatment until the zinc acetylacetonate is completely dissolved.

[0033] The method for preparing a 0.05 mol / L SnCl4 aqueous solution is as follows: Disperse an appropriate amount of SnCl4·5H2O solid powder in deionized water and stir until dissolved. Based on the volume of deionized water, add 20% (by mass) of 36.5% concentrated hydrochloric acid to the SnCl4 aqueous solution. Concentrated hydrochloric acid can inhibit the growth of Sn... 4+ It reacts with water to form a SnO2 suspension, which is then subjected to ultrasonic treatment until SnCl4·5H2O is completely dissolved.

[0034] Example 1 Preparation of highly crystalline and highly conductive ZnGa2O4 epitaxial thin films: (1) Take 48 mL of 0.05 mol / L gallium acetylacetonate aqueous solution, 50 mL of 0.05 mol / L zinc acetylacetonate aqueous solution and 2 mL of 0.05 mol / L SnCl4 aqueous solution and mix them evenly to obtain the precursor solution.

[0035] (2) The C-side 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. It was then fixed on the sample stage of the reaction chamber of the Mist-CVD equipment. The precursor solution was placed in the ultrasonic nebulizer (frequency of 2.4 MHz), and argon gas (flow rate of 7500 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 750 ℃ ​​and kept at that temperature for 15 min. The reaction chamber temperature was then maintained at 750 ℃ ​​for ultrasonic atomization growth for 1 h.

[0036] After ultrasonic atomization growth is completed, the ultrasonic atomizer is turned off and atomization is stopped; argon gas (flow rate of 1000 mL / min) is continued to be introduced as the annealing atmosphere, and the temperature is maintained at 750 ℃; the in-situ annealing time is controlled at 30 min. After the in-situ annealing is completed and the equipment cools to room temperature, the substrate is removed.

[0037] Example 2 Compared with Example 1, this embodiment adjusts the tin doping amount to obtain a ZnGa2O4 epitaxial film with high crystallinity and high conductivity. The specific process is as follows: (1) Take 46 mL of 0.05 mol / L gallium acetylacetonate aqueous solution, 50 mL of 0.05 mol / L zinc acetylacetonate aqueous solution and 4 mL of 0.05 mol / L SnCl4 aqueous solution and mix them evenly to obtain the precursor solution.

[0038] (2) The C-side 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. It was then fixed on the sample stage of the reaction chamber of the Mist-CVD equipment. The precursor solution was placed in the ultrasonic nebulizer (frequency of 2.4 MHz), and argon gas (flow rate of 7500 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 750 ℃ ​​and kept at that temperature for 15 min. The reaction chamber temperature was then maintained at 750 ℃ ​​for ultrasonic atomization growth for 1 h.

[0039] After ultrasonic atomization growth is completed, the ultrasonic atomizer is turned off and atomization is stopped; argon gas (flow rate of 1000 mL / min) is continued to be introduced as the annealing atmosphere, and the temperature is maintained at 750 ℃; the in-situ annealing time is controlled at 30 min. After the in-situ annealing is completed and the equipment cools to room temperature, the substrate is removed.

[0040] Comparative Example 1 Compared with Example 1, this comparative example does not dope tin and obtains a ZnGa2O4 epitaxial thin film. The specific process is as follows: (1) Take 50 mL of 0.05 mol / L gallium acetylacetonate aqueous solution and 50 mL of 0.05 mol / L zinc acetylacetonate aqueous solution and mix them evenly to obtain the precursor solution.

[0041] (2) The C-side 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. It was then fixed on the sample stage of the reaction chamber of the Mist-CVD equipment. The precursor solution was placed in the ultrasonic nebulizer (frequency of 2.4 MHz), and argon gas (flow rate of 7500 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 750 ℃ ​​and kept at that temperature for 15 min. The reaction chamber temperature was then maintained at 750 ℃ ​​for ultrasonic atomization growth for 1 h.

[0042] After ultrasonic atomization growth is completed, the ultrasonic atomizer is turned off and atomization is stopped; argon gas (flow rate of 1000 mL / min) is continued to be introduced as the annealing atmosphere, and the temperature is maintained at 750 ℃; the in-situ annealing time is controlled at 30 min. After the in-situ annealing is completed and the equipment cools to room temperature, the substrate is removed.

[0043] Comparative Example 2 Compared with Example 1, this comparative example adjusts the tin doping amount to obtain a ZnGa2O4 epitaxial thin film. The specific process is as follows: (1) Take 44 mL of 0.05 mol / L gallium acetylacetonate aqueous solution, 50 mL of 0.05 mol / L zinc acetylacetonate aqueous solution and 6 mL of 0.05 mol / L SnCl4 aqueous solution and mix them evenly to obtain the precursor solution.

[0044] (2) The C-side 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. It was then fixed on the sample stage of the reaction chamber of the Mist-CVD equipment. The precursor solution was placed in the ultrasonic nebulizer (frequency of 2.4 MHz), and argon gas (flow rate of 7500 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 750 ℃ ​​and kept at that temperature for 15 min. The reaction chamber temperature was then maintained at 750 ℃ ​​for ultrasonic atomization growth for 1 h.

[0045] After ultrasonic atomization growth is completed, the ultrasonic atomizer is turned off and atomization is stopped; argon gas (flow rate of 1000 mL / min) is continued to be introduced as the annealing atmosphere, and the temperature is maintained at 750 ℃; the in-situ annealing time is controlled at 30 min. After the in-situ annealing is completed and the equipment cools to room temperature, the substrate is removed.

[0046] Comparative Example 3 Compared with Example 1, this comparative example does not undergo in-situ annealing to obtain a ZnGa2O4 epitaxial film. The specific process is as follows: (1) Take 48 mL of 0.05 mol / L gallium acetylacetonate aqueous solution, 50 mL of 0.05 mol / L zinc acetylacetonate aqueous solution and 2 mL of 0.05 mol / L SnCl4 aqueous solution and mix them evenly to obtain the precursor solution.

[0047] (2) The C-side 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. It was then fixed on the sample stage of the reaction chamber of the Mist-CVD equipment. The precursor solution was placed in an ultrasonic nebulizer (frequency 2.4 MHz), and argon gas (flow rate 7500 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 750 ℃ ​​and held for 15 min. The reaction chamber temperature was then maintained at 750 ℃ ​​for ultrasonic atomization growth for 1 h. After ultrasonic atomization growth was completed, the ultrasonic nebulizer was turned off, atomization was stopped, the argon gas supply was stopped, and the equipment was cooled to room temperature before the substrate was removed.

[0048] Figure 1 X-ray diffraction (XRD) θ-2θ scan images of the highly crystalline and highly conductive ZnGa2O4 epitaxial films prepared in Examples 1-2 and Comparative Examples 1-3. Figure 1 In the diagram, the red dashed lines mark the diffraction peaks of the {111} crystal plane family of ZnGa2O4, and the green circles mark the diffraction peaks of SnO2. Compared to Example 1, the ZnGa2O4 epitaxial film prepared in Comparative Example 1 has lower diffraction peak intensities and poorer crystal quality, indicating that appropriate Sn doping helps improve the crystal quality of the ZnGa2O4 epitaxial film. Compared to Example 1, the ZnGa2O4 epitaxial film prepared in Comparative Example 2 contains SnO2 impurity phase, indicating that the 6 at% Sn doping concentration exceeds the solid solubility limit of Sn in ZnGa2O4. Therefore, Sn precipitates in the form of SnO2 at grain boundaries or inside grains. The presence of impurity phase severely damages the crystal structure and chemical homogeneity of the ZnGa2O4 epitaxial film, becoming a strong scattering center and defect source, leading to a sharp decline in crystal quality. The epitaxial film becomes porous, rough, and full of defects. Compared with Example 1, the intensity of the crystal plane diffraction peak of the ZnGa2O4 epitaxial film prepared in Comparative Example 3 was reduced, which indicates that in-situ annealing can improve the crystal quality of ZnGa2O4 epitaxial film to a certain extent.

[0049] Figure 2The current (I)-voltage (V) curves of the highly crystalline and highly conductive ZnGa2O4 epitaxial films prepared in Examples 1-2 and Comparative Examples 1 and 3 are shown. Figure 2 As can be seen, compared with Comparative Example 1, the conductivity of the ZnGa2O4 epitaxial film prepared in Example 1 is significantly improved. Under a bias voltage of 20 V, the current of the ZnGa2O4 epitaxial film prepared in Example 1 is 8.11 × 10⁻⁶. -6 A, The current of the ZnGa2O4 epitaxial film prepared in Comparative Example 1 is 2.30 × 10⁻⁶. -10 A; This indicates that appropriate Sn doping helps improve the conductivity of the ZnGa2O4 epitaxial film. Compared to Comparative Example 3, the conductivity of the ZnGa2O4 epitaxial film prepared in Example 1 is also improved. Under a bias voltage of 20 V, the current of the ZnGa2O4 epitaxial film prepared in Comparative Example 3 is 1.82 × 10⁻⁶. -6 A; This indicates that in-situ annealing can improve the conductivity of ZnGa2O4 epitaxial films to some extent.

[0050] Meanwhile, the ZnGa2O4 epitaxial film prepared in Example 2 exhibits a current of 2.71 × 10⁻⁶ under a bias voltage of 20 V. -9 A. By comparing the crystallinity and conductivity of the ZnGa2O4 epitaxial films prepared in Example 1 and Example 2, it can be seen that the ZnGa2O4 epitaxial film prepared in Example 1 has higher crystallinity and higher conductivity.

[0051] Tin element Sn 4+ The ions are introduced into the ZnGa₂O₄ lattice, replacing Ga. 3+The doping concentration of tin atoms at specific lattice positions can increase the concentration of free carriers by providing additional electrons, thereby improving the conductivity of the material. This is effectively achieved at a doping concentration of 2 at%. This is because: the number of doped tin atoms is relatively small, and their density as ionized impurity scattering centers is also low; although each tin atom, while providing free electrons, also becomes a positively charged Coulomb barrier that scatters electron motion, the probability of free electrons colliding with or being significantly scattered by these scattering centers is relatively low due to the large distance between them; therefore, the carrier mobility is maintained at a high level. At this stage, the significant increase in the concentration of free electrons introduced by doping is the dominant factor in the enhanced conductivity, completely masking the slight mobility loss caused by the presence of a small number of scattering centers. However, when the tin doping concentration was further increased to 4 at%, the situation changed; at this point, the density of tin atoms in the lattice, which act as ionized impurity scattering centers, doubled; this increase in the number of scattering centers was not a simple linear relationship, and the resulting scattering probability increased at an even faster rate; the lattice was filled with a large number of positively charged, regularly arranged Sn atoms. 4+ Ions form a dense and powerful Coulomb scattering field. When free electrons attempt to move directionally under the influence of the electric field, their paths are frequently deflected and disturbed by these closely distributed scattering centers. Each deflection means a loss of electron momentum and a change in direction, macroscopically manifested as a sharp decrease in carrier mobility. Ultimately, at a high doping concentration of 4 at%, although theoretically the concentration of free electrons may be higher than at 2 at%, the sharp increase in ionized impurity scattering severely restricts carrier mobility. Conductivity is the product of carrier concentration and mobility; when the decrease in mobility exceeds the potential gain from increased carrier concentration, overall conductivity deteriorates.

[0052] In this invention, the crystallinity and conductivity of ZnGa2O4 epitaxial films are synergistically improved by doping with an appropriate amount of tin and in-situ annealing. Specifically, the tin element is mainly Sn. 4+ Tin doping introduces ions into the ZnGa2O4 lattice, optimizing the crystal structure through substitutional doping. Regarding crystal quality, tin doping can adjust lattice parameters, reducing lattice mismatch between the epitaxial film and the C-plane sapphire substrate, thereby reducing stress and defect density during epitaxial growth and promoting more uniform and dense crystal growth. However, the concentration of tin doping must be controlled within the solid solubility limit; excessive doping leads to the precipitation of SnO2 impurity phases, damaging crystal integrity and hindering the improvement of crystal quality. Regarding conductivity, Sn… 4+ As an n-type dopant, ions replace Ga in ZnGa₂O₄ 3+When tin is applied to sites, additional free electrons are introduced, effectively increasing the carrier concentration and thus significantly improving the conductivity of the epitaxial film. However, excessive tin doping is not conducive to improving conductivity, and the sharp increase in ionized impurity scattering severely restricts the carrier migration ability. After ultrasonic atomization growth, in-situ annealing provides sufficient energy for the atoms inside the epitaxial film to migrate and rearrange. This adjustment of the atomic-level structure can effectively repair point defects and lattice distortions generated during rapid deposition, promote grain growth and grain boundary optimization, thereby reducing the crystal defect density and making the crystal structure of the epitaxial film more complete and ordered, significantly improving the crystal quality. At the same time, in the oxygen-deficient argon annealing atmosphere, oxygen atoms on the surface of the epitaxial film are more likely to detach from the lattice, thereby generating a certain concentration of oxygen vacancies inside the material. These oxygen vacancies can effectively act as n-type doping centers in ZnGa2O4, contributing free electrons and significantly increasing the carrier concentration. The increase in carrier concentration directly leads to the enhancement of the conductivity of the epitaxial film, which complements the effect of tin doping introducing additional carriers, synergistically achieving a leap in the conductivity of the epitaxial film by orders of magnitude.

[0053] 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 preparing a highly crystalline and highly conductive ZnGa2O4 epitaxial thin film, characterized in that, Includes the following steps: (1) A precursor solution is formed by mixing an aqueous solution of gallium acetylacetonate, an aqueous solution of zinc acetylacetonate, and an aqueous solution of tetravalent tin salt; (2) After cleaning and purging with nitrogen, the sapphire substrate is fixed in the reactor of the fog chemical vapor deposition equipment. The precursor solution is placed in the ultrasonic atomizer, the ultrasonic atomizer is turned on, and the crude ZnGa2O4 epitaxial film is obtained by ultrasonic atomization growth. Then, in-situ annealing is performed to obtain a ZnGa2O4 epitaxial film with high crystallinity and high conductivity.

2. The preparation method according to claim 1, characterized in that, The concentration of gallium acetylacetonate aqueous solution is 0.03~0.08 mol / L; The method for preparing 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 gallium acetylacetonate aqueous solution after sonication; wherein the mass fraction of hydrochloric acid is 36%~38%.

3. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the zinc acetylacetone aqueous solution is 0.03~0.08 mol / L; The preparation method of zinc acetylacetonate aqueous solution includes: mixing zinc acetylacetonate with deionized water and hydrochloric acid at a volume ratio of (90~110):1.5, and obtaining zinc acetylacetonate aqueous solution after sonication; wherein, the mass fraction of hydrochloric acid is 36%~38%.

4. The preparation method according to claim 1, characterized in that, In step (1), the tetravalent tin salt is selected from one of tin tetrachloride, tin sulfate, and tin bromide; The concentration of tetravalent tin salt aqueous solution is 0.03~0.08 mol / L; The method for preparing a tetravalent tin salt aqueous solution includes: mixing the tetravalent tin salt with deionized water and hydrochloric acid at a volume ratio of (90~110):20, and then sonicating the mixture to obtain a tetravalent tin salt aqueous solution; wherein the mass fraction of hydrochloric acid is 36%~38%.

5. The preparation method according to claim 1, characterized in that, In step (1), the volume ratio of the gallium acetylacetonate aqueous solution, the zinc acetylacetonate aqueous solution, and the tetravalent tin salt aqueous solution is (46~49.5):50:(4~0.5).

6. The preparation method according to claim 1, characterized in that, In step (2), the method for cleaning the sapphire substrate includes: ultrasonically cleaning the sapphire substrate in acetone, ethanol and deionized water in sequence; Each ultrasonic cleaning session lasts 3 to 8 minutes.

7. The preparation method according to claim 1, characterized in that, In step (2), the frequency of the ultrasonic atomizer is 1.7~2.4 MHz.

8. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the reactor chamber of the atomized chemical vapor deposition equipment is 700~750 ℃ ​​during the ultrasonic atomization growth process; the ultrasonic atomization growth time is 1~2 h.

9. The preparation method according to claim 1, characterized in that, In step (2), argon is used as a carrier gas to transport the atomized droplets to the reactor chamber of the atomized chemical vapor deposition equipment to undergo a reaction; In step (2), the in-situ annealing method includes: after stopping atomization, continuing to introduce argon gas as the annealing atmosphere and maintaining the temperature at 700~750 ℃; the in-situ annealing time is 20~40 min.

10. A highly crystalline and highly conductive ZnGa2O4 epitaxial thin film, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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