A method for preparing a tin-doped gallium oxide single crystal material

Abstract

This invention relates to the field of semiconductor material preparation technology, specifically a method for preparing tin-doped gallium oxide single crystal materials. The method includes sintering, loading, crystal growth, and cooling processes. By employing a segmented sintering process and optimizing the control of the doping composition, it effectively addresses issues such as tin volatilization, encapsulation, and powder agglomeration, ensuring uniform solid solution of tin in the gallium oxide lattice, guaranteeing the stability of the doping process, and improving the quality and performance of the sintered body. Furthermore, by controlling the process conditions during the heating and crystal growth stages, it further suppresses concentration fluctuations at the interface, promotes melt convection homogenization, and enhances the solid solubility and distribution consistency of tin in the β-Ga₂O₃ lattice. This, in turn, improves the overall performance of the β-Ga₂O₃ single crystal material, providing a high-quality, reproducible material basis for subsequent device fabrication and effectively meeting the urgent need for high-performance β-Ga₂O₃ single crystal substrates in power devices and deep-ultraviolet optoelectronic devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material preparation technology. More specifically, the purpose of this invention is to provide a method for preparing tin-doped gallium oxide single crystal material through a specific process. Background Technology

[0002] The ultra-wide bandgap semiconductor β-Ga2O3, with its high bandgap of 4.9 eV, has shown great application potential in high-power devices and optoelectronic devices. This material not only excels in manufacturing high-power electronic devices but also has broad application prospects in optoelectronic devices. Furthermore, β-Ga2O3 can be used to manufacture gas sensors and transparent conductive electrodes, further expanding its application range. Compared with third-generation semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN), β-Ga2O3 single crystals have a higher bandgap and lower single-crystal preparation costs. This material can be grown using melt methods, giving it significant industrial advantages in production. Because of these unique advantages, β-Ga2O3 has been hailed by the industry as a fourth-generation semiconductor material.

[0003] However, in the manufacturing of power devices, single-crystal substrates require doping to achieve high carrier concentrations. Existing doping methods are difficult to control during production, making it challenging to guarantee uniformity and compositional accuracy in large-size doping. These issues directly impact the quality of the final product, becoming a bottleneck restricting the application of β-Ga2O3 materials. Particularly during tin doping, the uneven concentration distribution and poor thermal stability of tin dopant are particularly prominent, making it difficult to precisely control the carrier concentration in the material.

[0004] To this end, the present invention proposes a method for preparing tin-doped gallium oxide single crystal materials. By optimizing the dopant source ratio, sintering process, material placement method and crystal growth process, the volatilization of dopant is reduced while the uniform distribution of tin in the β-Ga2O3 lattice can be achieved.

[0005] Journal article (Thin Solid Films, 2008, 516(17), 5763-5767) disclosed the use of Sn-doped β-Ga2O3 single crystals. However, due to the high volatility of tin oxide, even if 1 mol% of Sn is added in the raw material ratio, the Sn content in the obtained crystal is only on the order of 10 ppm. This not only brings great difficulty to controlling its content and uniformity, but also the volatilization of tin oxide will cause pollution to the preparation equipment, affecting the service life of the equipment and the purity of the crystal.

[0006] Therefore, it is urgent to develop a new method for preparing tin-doped gallium oxide single crystal materials to effectively solve technical problems such as easy volatilization of dopant elements, instability of the doping process, and poor uniformity of crystal doping, improve the stability and repeatability of the doping process, ensure the doping uniformity of large-size substrates, and thus significantly improve the overall performance of β-Ga2O3 materials. Summary of the Invention

[0007] To address at least one of the aforementioned technical problems, this invention provides a method for preparing tin-doped gallium oxide single crystal materials. This method achieves precise control over the doping process of β-Ga2O3 single crystal substrates through step-by-step sintering doping and adjustment of process parameters during crystal growth. This provides the possibility for large-scale production of uniformly doped large-size substrates and provides strong support for obtaining high-quality β-Ga2O3 materials and preparing high-performance power devices.

[0008] According to one aspect of the present invention, a method for preparing a tin-doped gallium oxide single crystal material is provided, the method comprising the following steps: Step S1: Sintering process. SnO2 and Ga2O3 powders are mixed according to the stoichiometric ratio, and pre-sintered at the first sintering temperature, and then sintered again at the second sintering temperature to obtain the SnO2-Ga2O3 composite sintered body; Ga2O3 is sintered once to obtain the Ga2O3 sintered body.

[0009] Following the sintering of the SnO2-Ga2O3 composite body, Ga2O3 is sintered once to form a densified pre-reacted bulk, effectively reducing the volatilization loss of Sn during subsequent crystal growth. By controlling the temperature profiles and holding times of the two sintering processes, the solid-state reaction is fully promoted, ensuring uniform dispersion of the dopant source. Subsequently, the resulting sintered body is placed in a crucible and placed in a crystal growth furnace for single crystal growth under directional solidification conditions. With the addition of trace amounts of oxidizing gas, the reduction and escape of Sn are further suppressed, achieving precise control of the doping concentration and highly repeatable distribution along the growth direction.

[0010] Step S2: Loading process. The SnO2-Ga2O3 composite sintered body and the pure Ga2O3 sintered body are assembled in the crystal growth crucible according to the growth requirements to form a layered filler structure. First, the SnO2-Ga2O3 composite sintered body is placed in the crucible, and then the gallium oxide sintered body is placed on top and the crucible lid is closed.

[0011] The inventors of this application creatively propose a specific layered filling method, in which a composite sintered body is placed in the lower layer as a dopant source, and a pure Ga2O3 sintered body is placed in the upper layer as the main raw material. The interface between the two is tightly bonded, ensuring a continuous supply of the dopant source during melting, maintaining a stable tin concentration in the melt, and providing a uniform compositional environment for single crystal growth, enabling precise control of the doping depth. Simultaneously, it reduces the volatilization loss of SnO2 at high temperatures during the heating and holding stage, avoiding localized compositional fluctuations caused by voids. By optimizing the layered distribution of the raw materials and the thermal field design within the crucible, stable gas phase equilibrium is ensured, suppressing the formation of impurity phases. Combined with a slow heating program, the dopant element gradually dissolves and diffuses uniformly during melting, improving the compositional stability at the solid-liquid interface. After growth, directional annealing is performed to eliminate thermal stress, obtaining a tin-doped β-Ga2O3 single crystal material with low defect density and high resistivity uniformity, meeting the requirements for large-size power device fabrication.

[0012] Step S3: Crystal Growth Process. The crucible containing the SnO2-Ga2O3 composite sintered body and the gallium oxide sintered body is placed in the crystal growth furnace. The temperature is initially raised to the crystal growth temperature range of 1750-1820℃ and held within this range for 3-5 hours. During the holding process, a first crucible rotation speed is set to ensure sufficient fusion of SnO2 and Ga2O3. Subsequently, a reduced second crucible rotation speed is set during the crystal growth process to promote continuous and stable single crystal growth.

[0013] The first rotational speed is 5-20 rpm. A higher first crucible rotational speed is set during the holding process to promote radial compositional uniformity, maintain the uniform distribution of doped elements within the melt, and reduce surface disturbance. The second rotational speed is reduced to 1-4 rpm. A lower second crucible rotational speed is set during crystal growth to establish a stable temperature gradient at the crystal growth interface, suppressing compositional supercooling and parasitic nucleation, and ensuring continuous and stable single crystal growth. The entire growth process is carried out under a specific oxygen atmosphere, with the oxygen partial pressure controlled at 1-1.5 bar, effectively maintaining the Sn... 4+ Oxidation stability.

[0014] Step S4: Cooling process. After crystal growth is completed, the crystal is slowly cooled to room temperature in the furnace. The doped gallium oxide single crystal is then removed from the crucible for subsequent testing and processing.

[0015] During the cooling process, to avoid internal stress caused by sudden temperature changes that could affect crystal quality, it is necessary to precisely control the dynamic matching between the cooling rate and the crucible rotation rate to guide the smooth advancement of the solid-liquid interface and suppress radial component segregation. After growth, the crystal is first slowly cooled to below 1200℃ at a first cooling rate of 0.5-1.5℃ / h for directional annealing to release lattice stress and reduce dislocation density. Then, it is further cooled to room temperature at a second cooling rate to obtain tin-doped Ga2O3 single crystals with a diameter ≥2 inches and a thickness ≥20 mm.

[0016] In one embodiment of the present invention, step S1 further includes the following sub-steps: Step S101: Mixing process: High-purity Ga2O3 powder and SnO2 dopant are mixed according to a predetermined stoichiometric ratio and placed in a ball mill jar. The amount of SnO2 added is kept to be the sum of the expected doping amount and the volatility compensation amount. Deionized water is added as a dispersion medium, and zirconia microspheres are used as the ball milling medium to ensure that the raw materials are fully and uniformly mixed. The Ga2O3 powder is weighed for later use.

[0017] Step S102: Forming process. The mixed powder obtained after ball milling is fed into a press and cold-formed by isostatic pressing or unidirectional pressing to press the powder into a mixed powder blank with uniform density. The shape and size of the mixed powder blank are matched with the inner cavity of the crucible to facilitate densification during subsequent sintering.

[0018] Step S103: Sintering process of SnO2-Ga2O3 composite sintered body. The trimmed mixed powder blank is loaded into a high-purity alumina crucible, ensuring that the bottom is flat and in contact, avoiding tilting. First, the temperature is increased to the first heating temperature at a rate of 1-5℃ / min, and sintered for more than 2 hours. Then, the raw material sintered in the first step is crushed, ball-milled again, and pressed into shape. Then, the temperature is increased to the second heating rate at a rate of 1-5℃ / min, and sintered for 24 hours.

[0019] Step S104: Sintering process of Ga2O3 sintered body. The Ga2O3 powder weighed in step S101 is separately loaded into another high-purity alumina crucible and sintered at a temperature range of 1650-1700℃ for more than 24 hours, preferably more than 36 hours, to obtain a dense pure Ga2O3 sintered body.

[0020] In one embodiment of the present invention, in step S1, the expected doping amount of the SnO2 dopant is 1:99, and the volatilization compensation amount is 10% to 50% of the expected doping amount to offset the volatilization loss of Sn element during high-temperature growth. The stoichiometric ratio of the SnO2 dopant to the Ga2O3 powder can be selected as 1.1:98.9, or 1.5:98.5, or 1.8:98.2, or 2:98.

[0021] In one embodiment of the present invention, in step S1, both the first heating temperature and the second heating temperature are below 1600℃. Optionally, the first heating temperature is controlled within the range of 1400-1500℃ to allow the mixed powder to be initially sintered into a porous ceramic body, retaining a certain porosity to facilitate subsequent high-temperature densification. The second heating temperature is controlled within the range of 1500-1580℃ for secondary sintering, promoting intergranular diffusion, achieving densification of the green body, and obtaining a sintered body with a density greater than 95% of the theoretical density. The entire sintering process lasts for more than 20 hours, with a heating rate of 3-5℃ / min.

[0022] In one embodiment of the present invention, in step S102, the pressing pressure is controlled between 100-300 MPa, and the pressure is maintained for 3-10 minutes to avoid delamination or density gradients. The thickness of the mixed powder preform is about 5-15 mm, and then the surface is trimmed to remove burrs and edge defects to ensure stacking stability during the loading process and reduce thermal distortion caused by poor contact.

[0023] In one embodiment of the present invention, in step S103, the first sintering time is preferably 2 hours or more to ensure sufficient diffusion and uniform distribution of the dopant elements, more preferably 8 hours or more to fully remove moisture and impurities from the mixed powder, even more preferably 16 hours or more to allow preliminary solid solution to form between the mixed powder particles, and most preferably 24 hours or more to achieve complete solid solution between the dopant and the matrix material. After the second ball milling, the particle size of the mixed powder is controlled below 50 μm to ensure good flowability and uniform filling density during loading. The sintering process is carried out in an air atmosphere to avoid decomposition of Ga2O3 caused by a reducing atmosphere. The powder structure after two pre-sintering treatments is dense and the composition is uniform, significantly reducing the concentration gradient and defect density in subsequent crystal growth, providing a high-purity and uniform raw material basis for the preparation of high-quality β-Ga2O3 single crystals.

[0024] The purpose of sintering is to induce a solid-state reaction between gallium oxide and tin oxide to form a polycrystalline material. SnO2 has a melting point of 1630℃. If the sintering temperature exceeds 1500℃, it will volatilize violently. If the sintering temperature is too low, it is difficult to achieve effective sintering of the two materials, and the density will be low, reducing the crucible's capacity. Furthermore, traditional low-temperature single-step sintering processes are prone to problems such as encapsulation and powder agglomeration. Therefore, this invention proposes a two-step sintering scheme based on traditional solid-state synthesis processes.

[0025] In the first stage, the initial heating temperature is, for example, 1400-1485℃ (0.85-0.91 times the melting point of SnO2). This temperature is maintained for at least 24 hours to remove impurities such as adsorbed water, crystal water, and organic matter from the powder, promoting initial bonding between powder particles, ensuring sufficient solid solution of dopant elements, and forming a uniform SnO2-Ga2O3 composite sintered body. Simultaneously, excessive SnO2 volatilization is suppressed, laying the foundation for subsequent high-temperature sintering. The pre-sintered body is then removed and pulverized, followed by ball milling for 5-10 hours to refine the grains, improve compositional uniformity, and enhance charge flowability. In the second stage, the temperature is raised to 1500-1550℃ and maintained for 24 hours for high-temperature sintering. This promotes sufficient densification between particles and grain growth, forming a high-density, low-defect polycrystalline SnO2-Ga2O3 ceramic body. The high-temperature sintering stage is crucial for achieving a good sintered body structure. The two-step sintering process effectively suppresses or reduces the volatilization of tin oxide, decreases porosity and inclusion defects, and to some extent avoids problems such as encapsulation and heterogeneous phase formation, thereby improving the density and reaction uniformity of the raw materials and enhancing the crystallinity and structural stability of the material. Simultaneously, by controlling the heating rate and holding time, the grain boundary structure is further optimized, improving the material's density. X-ray diffraction analysis shows that Sn is uniformly dissolved in the crystal lattice, with no obvious impurity phase peaks. Microstructure reveals a uniform grain distribution with an average grain size of approximately 2-5 μm, a porosity of less than 3%, and a density exceeding 96% of the theoretical density.

[0026] In one embodiment of the present invention, in step S3, the first rotation speed is 5-20 rpm, preferably 6-15 rpm, and more preferably 10-12 rpm. Setting a higher first crucible rotation speed during the heat preservation process aims to promote radial compositional uniformity, maintain melt homogeneity, and reduce surface disturbance. The second rotation speed is reduced to 1-4 rpm, preferably 1.2-3.6 rpm, and more preferably 1.5-3 rpm. Setting a lower second crucible rotation speed during crystal growth allows for the establishment of a stable temperature gradient at the crystal growth interface, suppressing compositional supercooling and parasitic nucleation, and ensuring continuous and stable single crystal growth. The crystal growth process is preferably carried out under a certain oxygen atmosphere, with the oxygen partial pressure controlled at 1-1.5 bar, to suppress the dissociation of SnO2 and maintain the stable solid solution of Sn in the crystal lattice.

[0027] In one embodiment of the present invention, in step S4, a segmented cooling method is adopted. First, the temperature is slowly reduced to below 1400℃, preferably 1200℃-1400℃, at a first cooling rate of 0.5-3℃ / h for directional annealing to release lattice stress and reduce dislocation density. The annealing time is 6-12 hours. Then, the temperature is further reduced to 800℃ at a second cooling rate of 0.5-2℃ / min to further repair point defects and dislocations generated during growth and improve the integrity of the single crystal. Subsequently, the crystal is naturally cooled to room temperature in the furnace to obtain a tin-doped Ga2O3 single crystal with a diameter ≥2 inches and a thickness ≥20 mm. The crystal surface is smooth and free of cracks and gas line defects. The annealing process is preferably carried out in a high-purity oxygen atmosphere to compensate for oxygen vacancies that may occur at high temperatures and maintain the stable valence state of Ga in the lattice.

[0028] In another embodiment of the present invention, step S1 may include more heating stages to achieve gradient pre-sintering treatment of the raw materials. Optionally, the first heating stage is held at 600-800℃ for 2-4 hours to remove adsorbed water and organic matter, preventing the generation of bubbles or cracks during subsequent melting; the second heating stage is heated to 1000-1200℃ and held for 3-5 hours to promote the initial reaction; the third stage raises the furnace temperature to 1400-1485℃ to initially form a solid solution phase and eliminate local concentration gradients; the fourth stage continues to heat to 1500-1550℃ and holds for more than 24 hours for high-temperature sintering, promoting sufficient densification between particles and grain growth to form a high-density, low-defect polycrystalline SnO2-Ga2O3 ceramic body. The heating rate of each stage is controlled at 1-5℃ / min to avoid powder agglomeration or uneven reaction due to thermal shock. Those skilled in the art can adjust the heating stage according to actual production needs. Multi-stage heating design can effectively improve the purity and reactivity of the synthesized powder, providing structurally stable and uniformly composed initial materials for subsequent high-temperature sintering.

[0029] In another embodiment of the invention, a back-reflective heat shield can be introduced to optimize the axial temperature gradient, reduce thermal disturbance at the crystal growth interface, and thus improve crystal quality and interface stability. By adjusting the position and curvature of the reflective shield, the thermal field distribution within the furnace can be precisely controlled, making the solid-liquid interface more planar and suppressing the tendency for component supercooling and cellular growth. Combined with directional solidification technology, this design effectively reduces axial temperature gradient fluctuations, improves the consistency of crystal growth rate, and reduces microcracks and slip defects caused by thermal stress accumulation. Simultaneously, the reflective shield material is high-purity zirconium oxide, which possesses excellent high-temperature resistance and low thermal radiation absorption rate, maintaining stable thermal performance during long-term operation and further ensuring the uniformity and controllability of the crystal growth environment.

[0030] According to another aspect of the present invention, a tin-doped Ga2O3 single crystal is provided, which can be prepared according to the method described in any embodiment of the first aspect. The tin-doped Ga2O3 single crystal has a tin doping molar ratio of approximately 1:99 and a tin burn-off rate of 10% to 50%.

[0031] According to another aspect of the present invention, a power device based on the tin-doped Ga2O3 single crystal is also provided, including but not limited to field-effect transistors, diodes, or deep ultraviolet photodetectors. According to the present invention, since the power device uses the aforementioned tin-doped Ga2O3 single crystal thin film as the core material, it exhibits excellent electrical performance and reliability, making it suitable for next-generation power electronics and optoelectronic applications.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The method for preparing tin-doped gallium oxide single crystal material of the present invention, through a step-by-step sintering doping process, minimizes problems such as tin oxide volatilization, encapsulation, and powder agglomeration, ensuring that tin element is uniformly dissolved in the gallium oxide lattice, achieving a good sintered body structure, and improving the quality and performance of the sintered body.

[0033] 2. This invention, by optimizing the control of doping components, not only ensures the stability of the doping process but also improves the accuracy of component control. This improvement helps to achieve a more precise doping ratio and a more stable doping effect, thereby further enhancing the overall performance of β-Ga2O3 materials.

[0034] 3. This invention controls the process conditions of the heating and holding stage and the holding-and-growth stage, including using a specific placement method to reduce volatilization and control the doping depth during the heating and holding stage, and controlling the crucible rotation speed and temperature field distribution during the holding-and-growth stage, thereby further suppressing concentration fluctuations at the interface and promoting melt convection homogenization, thereby improving the solid solubility and distribution consistency of tin in the β-Ga2O3 lattice, and thus improving the crystal growth efficiency and yield.

[0035] 4. This invention ensures the consistency of substrate doping concentration by controlling the process parameters of sintering doped crystal growth, which is crucial for the large-scale production and development of single-crystal substrates. Simultaneously, it provides a high-quality, reproducible material basis for subsequent device fabrication, effectively meeting the urgent demand for high-performance β-Ga2O3 single-crystal substrates in power electronics and deep-ultraviolet optoelectronic devices.

[0036] The above description is merely an overview of the technical solutions of the embodiments of this application. In order to better understand the technical means of the embodiments of this application and to implement them in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the embodiments of this application more obvious and understandable, specific implementation methods of the embodiments of this application are described below. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are merely some exemplary embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the content of the exemplary embodiments of the present invention and these drawings without any creative effort.

[0038] Figure 1 This is a flowchart illustrating one embodiment of the present invention. Figure 1 The process shown includes steps such as sintering, loading, crystal growth, and cooling.

[0039] Figure 2 This is a schematic flowchart of another embodiment of the present invention. The sintering process further includes several sub-steps, including a mixing process, a forming process, a SnO2-Ga2O3 composite sintering process, and a Ga2O3 sintering process.

[0040] Figure 3 shows the test results of the tin doping ratio of gallium oxide single crystal in the embodiment of the present invention. The test results show that the tin doping concentration is about 1%, which reaches the predetermined doping ratio, and the lateral distribution uniformity deviation is less than 8%. Invention Details The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Those skilled in the art will appreciate that many technical details have been provided in the various embodiments of the present invention to facilitate a better understanding of the invention. However, the technical solutions claimed in this invention can be implemented even without these technical details and with various variations and modifications based on the following embodiments.

[0042] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0043] Unless otherwise stated, the terms “include,” “including,” “have,” “contain,” etc., used in this document are open-ended terms, meaning that they include but are not limited to.

[0044] It should be understood that, for the numerical range in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Detailed Implementation

[0045] See Figure 1 , Figure 1 A detailed flow chart illustrating the preparation process of tin-doped Ga2O3 single crystals involved in this invention is provided. The method includes the following steps: Step S1: Sintering process. SnO2 and Ga2O3 powders are mixed according to the stoichiometric ratio, and pre-sintered at the first sintering temperature, and then sintered again at the second sintering temperature to obtain the SnO2-Ga2O3 composite sintered body. By controlling the temperature curves and holding time of the two sintering processes, the solid-phase reaction is promoted to proceed fully and the dopant source is uniformly dispersed. In step S1, the stoichiometric ratio of the SnO2 dopant to the Ga2O3 powder is greater than the molar ratio calculated according to the theoretical doping amount, in order to offset the volatilization loss of Sn element during high-temperature growth. For example, if the expected doping amount of the SnO2 dopant is 1:99, and the volatilization loss is approximately 10% to 50% of the expected doping amount, then the stoichiometric ratio of the SnO2 dopant to the Ga2O3 powder can be designed as 1.1:98.9, or 1.5:98.5, or 1.8:98.2, or 2:98.

[0046] For Ga2O3 powder, a single sintering process is performed to obtain a Ga2O3 sintered body.

[0047] In step S1, the purpose of sintering is to induce a solid-state reaction between gallium oxide and tin oxide to form a polycrystalline material. SnO2 has a melting point of 1630°C. If the sintering temperature exceeds 1600°C, it will volatilize violently. Therefore, both the first and second heating temperatures are below 1600°C. Furthermore, if the sintering temperature is too low, it is difficult to achieve effective sintering of the two materials, and the density will be low, reducing the crucible's capacity. Therefore, both the first and second heating temperatures must be controlled to be no lower than 1400°C. Moreover, when using the traditional low-temperature single-step sintering process, problems such as encapsulation and powder agglomeration are prone to occur. Therefore, this invention proposes a two-step sintering scheme based on the traditional solid-state synthesis process.

[0048] Optionally, the first heating temperature is controlled within the range of 1400-1500℃ to initially sinter the mixed powder into a porous ceramic body, retaining a certain porosity to facilitate subsequent high-temperature densification. The second heating temperature is controlled within the range of 1500-1580℃, and high-temperature sintering is carried out in an atmospheric atmosphere to promote intergranular diffusion, achieve densification of the green body, and obtain a composite sintered body with a density greater than 95% of the theoretical density. The entire sintering process lasts for more than 48 hours, with a heating rate of 1-5℃ / min, effectively avoiding cracking and deformation. The high-temperature sintering stage is crucial for achieving a good sintered body structure. The two-step sintering scheme effectively suppresses or reduces the volatilization of tin oxide, reduces porosity and inclusion defects, and to some extent avoids problems such as encapsulation and heterogeneous phase formation, improving the density and reaction uniformity of the raw materials, and enhancing the crystallinity and structural stability of the material. Simultaneously, by controlling the heating rate and holding time, the grain boundary structure is further optimized, improving the material's density.

[0049] Step S2: Loading process. The SnO2-Ga2O3 composite sintered body and the pure Ga2O3 sintered body are assembled in the crystal growth crucible according to the growth requirements to form a layered filler structure. First, the SnO2-Ga2O3 composite sintered body is placed in the crucible, and then the gallium oxide sintered body is placed on top and the crucible lid is closed.

[0050] The inventors of this application creatively propose a specific layered filling method, in which a composite sintered body is placed in the lower layer as a dopant source, and a pure Ga2O3 sintered body is placed in the upper layer as the main raw material. The interface between the two is tightly bonded, ensuring a continuous supply of the dopant source during melting, maintaining a stable tin concentration in the melt, and providing a uniform compositional environment for single crystal growth, enabling precise control of the doping depth. Simultaneously, it reduces the volatilization loss of SnO2 at high temperatures during the heating and holding stage, avoiding localized compositional fluctuations caused by voids. By optimizing the layered distribution of the raw materials and the thermal field design within the crucible, stable gas phase equilibrium is ensured, suppressing the formation of impurity phases. Combined with a slow heating program, the dopant elements gradually dissolve and diffuse uniformly during melting, improving the compositional stability at the solid-liquid interface. After growth, directional annealing is performed to eliminate thermal stress, obtaining a tin-doped Ga2O3 single crystal material with low defect density and high resistivity uniformity, meeting the requirements for large-size power device fabrication.

[0051] Step S3: Crystal Growth Process. The crucible containing the SnO2-Ga2O3 composite sintered body and the gallium oxide sintered body is placed in the crystal growth furnace. The temperature is initially raised to the crystal growth temperature range of 1750-1820℃ and held within this range for 3-5 hours. During the holding process, a first crucible rotation speed is set to ensure sufficient fusion of SnO2 and Ga2O3. Subsequently, a reduced second crucible rotation speed is set during the crystal growth process to promote continuous and stable single crystal growth.

[0052] During the heat preservation process, a relatively high first crucible rotation speed is set, maintained at 5-20 rpm, preferably 6-15 rpm, and more preferably 10-12 rpm. This aims to promote radial compositional uniformity, maintain the uniform distribution of doped elements within the melt, and reduce surface disturbance. During crystal growth, a lower second crucible rotation speed is set, reduced to 1-4 rpm, preferably 1.2-3.6 rpm, and more preferably 1.5-3 rpm. This establishes a stable temperature gradient at the crystal growth interface, suppressing compositional supercooling and parasitic nucleation, ensuring continuous and stable single crystal growth. The crystal growth process is preferably carried out under a specific oxygen atmosphere, with the oxygen partial pressure controlled at 1-1.5 bar, to suppress SnO2 dissociation and maintain stable solid solution of Sn in the crystal lattice.

[0053] Step S4: Cooling process. After crystal growth is completed, the crystal is slowly cooled to room temperature in the furnace. The doped gallium oxide single crystal is then removed from the crucible for subsequent testing and processing.

[0054] To avoid internal stress caused by sudden temperature changes during the cooling process, which could affect crystal quality, a segmented cooling method is preferred. First, the temperature is slowly lowered to below 1400°C at a first cooling rate, preferably within the range of 1200-1400°C, for directional annealing to release lattice stress and reduce dislocation density. The annealing time is 6-12 hours. Then, cooling continues to room temperature at a second cooling rate to obtain a tin-doped Ga2O3 single crystal with a diameter ≥2 inches and a thickness ≥20 mm. The second cooling rate is less than or equal to the first cooling rate; for example, the first cooling rate is in the range of 0.5-3°C / min, and the second cooling rate is controlled within the range of 0.5-2°C / min to avoid thermal stress concentration that could lead to crystal cracking or the formation of micro-defects.

[0055] Preferably, the second cooling rate continues to slowly cool to 800°C to further repair point defects and dislocations generated during growth, improving the integrity of the single crystal. It is then naturally cooled to room temperature in the furnace to obtain a tin-doped Ga₂O₃ single crystal with a diameter ≥ 2 inches and a thickness ≥ 20 mm, exhibiting a smooth surface free of cracks and gas line defects. The annealing process is preferably carried out in an oxygen atmosphere to compensate for oxygen vacancies that may occur at high temperatures, maintaining the stable valence state of Ga in the crystal lattice.

[0056] See Figure 2 , Figure 2 A detailed process flow diagram of the preparation process of tin-doped Ga2O3 single crystal according to another embodiment of the present invention is shown. Step S1 further includes the following sub-steps: Step S101: Mixing process: High-purity Ga2O3 powder and SnO2 dopant are mixed according to a predetermined stoichiometric ratio and placed in a ball mill jar. The amount of SnO2 added is kept to be the sum of the expected doping amount and the volatility compensation amount. Deionized water is added as a dispersion medium, and zirconia microspheres are used as the ball milling medium to ensure that the raw materials are fully and uniformly mixed. The Ga2O3 powder is weighed for later use.

[0057] The expected doping amount of the SnO2 dopant is 1:99, and the volatilization compensation amount is 10% to 50% of the expected doping amount to offset the volatilization loss of Sn element during high-temperature growth. The stoichiometric ratio of the SnO2 dopant to Ga2O3 powder can be selected as 1.1:98.9, 1.5:98.5, 1.8:98.2, or 2:98.

[0058] Step S102: Forming process. The mixed powder obtained after ball milling is fed into a press and cold-formed by isostatic pressing or unidirectional pressing to press the powder into a mixed powder blank with uniform density. The shape and size of the mixed powder blank are matched with the inner cavity of the crucible to facilitate densification during subsequent sintering.

[0059] The pressing pressure is controlled between 100-300 MPa, and the pressure is held for 3-10 minutes to avoid delamination or density gradients. The thickness of the mixed powder preform is about 5-15 mm, and then the surface is trimmed to remove burrs and edge defects to ensure stacking stability during the loading process and reduce thermal distortion caused by poor contact.

[0060] Step S103: Sintering process of SnO2-Ga2O3 composite sintered body. The trimmed mixed powder blank is loaded into a high-purity alumina crucible, ensuring that the bottom is flat and in contact, avoiding tilting. First, the temperature is increased to the first heating temperature at a rate of 1-5℃ / min, and sintered for more than 2 hours. Then, the raw material sintered in the first step is crushed, ball-milled again, and pressed into shape. Then, the temperature is increased to the second heating temperature at a rate of 1-5℃ / min, and sintered for more than 18 hours.

[0061] In the first stage, the initial heating temperature is, for example, 1400-1485℃ (0.85-0.91 times the melting point of SnO2). This temperature is maintained for at least 24 hours to remove impurities such as adsorbed water, crystal water, and organic matter from the powder, promoting initial bonding between powder particles, ensuring sufficient solid solution of dopant elements, and forming a uniform SnO2-Ga2O3 composite sintered body. Simultaneously, excessive volatilization of SnO2 is suppressed, laying the foundation for subsequent high-temperature sintering. The pre-sintered body is then removed, pulverized, and ball-milled again for 5-10 hours to refine the grains, improve compositional uniformity, and enhance charge flowability. In the second stage, the temperature is raised to 1500-1550℃ and maintained for at least 24 hours for high-temperature sintering, promoting sufficient densification between particles and grain growth to form a high-density, low-defect polycrystalline SnO2-Ga2O3 ceramic body.

[0062] The preferred first sintering time is 2 hours or more to ensure sufficient diffusion and uniform distribution of the dopant elements; more preferably, 8 hours or more to fully remove moisture and impurities from the mixed powder; even more preferably, 16 hours or more to allow preliminary solid solution to form between the mixed powder particles; and most preferably, 24 hours or more to achieve complete solid solution between the dopant and the matrix material. After a second ball milling, the particle size of the mixed powder is controlled below 50 μm to ensure good flowability and uniform filling density during loading. The preferred second sintering time is 24 hours or more, or 36 hours or more, or 48 hours or more to ensure a dense SnO2-Ga2O3 composite sintered body. The sintering process is carried out in an air atmosphere to avoid the decomposition of Ga2O3 caused by a reducing atmosphere. The powder structure after two pre-sintering treatments is dense and the composition is uniform, significantly reducing the concentration gradient and defect density in subsequent crystal growth, providing a high-purity and uniform raw material basis for the preparation of high-quality Ga2O3 single crystals.

[0063] Step S104: Sintering process of Ga2O3 sintered body. The Ga2O3 powder weighed in step S101 is separately loaded into another high-purity alumina crucible and sintered at a temperature range of 1650-1700℃ for more than 24 hours, preferably more than 36 hours, to obtain a dense pure Ga2O3 sintered body.

[0064] In another embodiment of the present invention, step S1 may further include multiple heating stages to achieve gradient pre-sintering treatment of the raw materials. Optionally, the first heating stage is held at 600-800℃ for 2-4 hours to remove adsorbed water and organic matter, preventing bubbles or cracks from forming during subsequent melting; the second heating stage is heated to 1000-1200℃ and held for 3-5 hours to promote the initial reaction; the third stage raises the furnace temperature to 1400-1485℃ to initially form a solid solution phase and eliminate local concentration gradients. After the temperature stabilizes, it is held for 15-20 hours to ensure complete homogeneity of the composition and eliminate local concentration gradients; the fourth stage continues to heat to 1500-1550℃ and is held for more than 24 hours for high-temperature sintering, promoting sufficient densification between particles and grain growth to form a high-density, low-defect polycrystalline SnO2-Ga2O3 ceramic body. The heating rate of each stage is controlled at 1-5℃ / min to avoid powder agglomeration or uneven reaction due to thermal shock. Those skilled in the art can adjust the heating stage according to actual production needs. Multi-stage heating design can effectively improve the purity and reactivity of the synthesized powder, providing structurally stable and uniformly composed initial materials for subsequent high-temperature sintering.

[0065] In another embodiment of the invention, step S3 can further incorporate a back-reflective heat shield to optimize the axial temperature gradient, reduce thermal disturbance at the crystal growth interface, and thus improve crystal quality and interface stability. By adjusting the position and curvature of the reflective shield, the thermal field distribution within the furnace can be precisely controlled, making the solid-liquid interface more planar and suppressing the tendency for component supercooling and cellular growth. Combined with directional solidification, this design effectively reduces axial temperature gradient fluctuations, improves the consistency of crystal growth rate, and reduces microcracks and slip defects caused by thermal stress accumulation. Simultaneously, the reflective shield material is high-purity zirconium oxide, which possesses excellent high-temperature resistance and low thermal radiation absorption rate, maintaining stable thermal performance during long-term operation and further ensuring the uniformity and controllability of the crystal growth environment.

[0066] Figure 3 shows the test results of the tin doping ratio of gallium oxide single crystal in the embodiment of the present invention. The test results show that the tin doping concentration is about 1%, the tin doping molar ratio is about 1:99, which achieves the predetermined doping ratio, and the lateral distribution uniformity deviation is less than 8%. The tin burn-off rate is 10% to 50%, proving that the burn-off setting of 0.1-1%mol in the sintering process and crystal growth process of the present invention is reasonable and controllable.

[0067] The power devices based on the tin-doped Ga2O3 single crystal according to the present invention include, but are not limited to, field-effect transistors, diodes, or deep ultraviolet photodetectors. According to the present invention, since the power devices use the aforementioned tin-doped Ga2O3 single crystal thin film as the core material, they exhibit excellent electrical performance and reliability, making them suitable for next-generation power electronics and optoelectronic applications.

[0068] Example 1 This embodiment provides a method for preparing tin-doped gallium oxide, which includes the following steps: Step S101: Mixing process The molar ratio of tin doping in gallium oxide was set at 1:99. Considering the easy burn-off of SnO2, the initial molar ratio of SnO2 to Ga2O3 was set at 1.5:98.5 (burn-off amount approximately 0.5% mol). 59.03 g of Ga2O3 and 0.97 g of SnO2 were weighed according to this mixing molar ratio and mixed to obtain 60 g of SnO2-Ga2O3 mixed powder. The mixed powder was placed in a ball mill jar and placed in a planetary ball mill. The ball mill speed was set to 100 rpm. Deionized water was added as the dispersion medium, and zirconia balls were used as the ball milling medium. The zirconia balls had three diameters: φ5, φ3, and φ1, with a mass ratio of 1:1:2 and a ball-to-material ratio of 2:1. The ball milling time was 5 hours to ensure uniform mixing and consistent particle size distribution of the raw materials. The ball-milled mixed powder was then dried at 80°C for 6 hours to remove moisture, resulting in a uniformly dried SnO2-Ga2O3 mixed powder.

[0069] Weigh out 20g of Ga2O3 powder for later use.

[0070] Step S102: Forming process The SnO2-Ga2O3 mixed powder obtained in the previous step was fed into a press and cold-formed using isostatic pressing. The forming pressure range was 100 MPa, and the holding pressure was maintained for 8-10 min. The resulting SnO2-Ga2O3 composite powder preform was in the shape of a disc, with a diameter of 25 mm, slightly smaller than the diameter of the crystal growth crucible. Each disc was 7 mm thick, weighed approximately 10 g, and had a density of 3.0 g / cm³. 3 The surface of the SnO2-Ga2O3 composite powder preform is trimmed to remove burrs and edge defects, in order to ensure stacking stability during the loading process and reduce thermal distortion caused by poor contact.

[0071] Step S103: Sintering process of SnO2-Ga2O3 composite sintered body The trimmed mixed powder blank is placed into a high-purity alumina crucible, ensuring a flat bottom and avoiding tilting. First, the SnO2-Ga2O3 composite powder blank is sintered at a first sintering temperature of 1480℃ at a rate of 1-3℃ / min for 24 hours to remove adsorbed water, crystal water, and organic matter, and to promote initial bonding between powder particles, laying the foundation for subsequent high-temperature sintering. Then, the first-sintered raw material is pulverized, ball-milled again for 5 hours, and pressed into shape again following the same procedure as step S102. Finally, the temperature is increased to a second sintering temperature of 1520℃ at a rate of 1-3℃ / min, and sintered for 24 hours.

[0072] Step S104: Sintering process of gallium oxide sintered body (Ga2O3) The Ga2O3 powder prepared in step S101 was sintered by placing it separately into another high-purity alumina crucible and sintering it at 1680℃ for 36 hours to obtain a gallium oxide sintered body.

[0073] Step S2: Loading process The SnO2-Ga2O3 composite sintered body obtained in step S103 and the gallium oxide sintered body obtained in step S104 are assembled in a clean environment according to actual growth requirements, and then placed sequentially into a crystal growth crucible and covered with a crucible lid. In this embodiment, the crucible size is 1 inch, and the total weight of the materials in the crucible is 80g. To reduce the volatilization of SnO2 in the sintered body during the heating process, the composite sintered body (SnO2+Ga2O3) is covered with gallium oxide sintered body (Ga2O3). The weight of the SnO2-Ga2O3 composite sintered body at the bottom is 60g, and the weight of the gallium oxide sintered body (Ga2O3) at the top is 20g. The SnO2-Ga2O3 composite sintered body is placed at the bottom as a dopant source, and the pure gallium oxide sintered body is placed at the top as the growth host. The two are in close contact to ensure the stability of heat conduction and mass transfer. After loading, the crucible is sealed and sent into a single crystal furnace, ready for subsequent crystal growth.

[0074] Step S3: Crystal growth process A crucible containing the SnO2-Ga2O3 composite sintered body and the gallium oxide sintered body was placed in a crystal growth furnace. To ensure uniform doping distribution, the crucible was kept rotating during melt holding and crystal growth. First, the temperature was raised to the crystal growth temperature and held at 1800℃ for 3.5 hours. During this holding period, the first rotation speed was set to 6 rpm to ensure that the SnO2 and Ga2O3 raw materials were fully melted and reached thermal equilibrium. Then, the crystal growth stage began, with a gradient cooling process controlled at a rate of 0.5℃ / h. The second rotation speed was reduced to 2.4 rpm to minimize the impact of thermal convection on the crystal growth interface and promote continuous and stable single crystal growth.

[0075] Step S4: Cooling process After crystal growth, the crystal is slowly cooled to room temperature in the furnace to avoid internal stress caused by sudden temperature changes, which could affect crystal quality. The crystal is then removed from the crucible to obtain a doped gallium oxide single crystal. Testing showed that the actual doping molar ratio was very close to 1:99, indicating that the 0.5% mol burn-off setting for this sintering and crystal growth process is reasonable.

[0076] The method for preparing tin-doped gallium oxide crystals in this embodiment employs a two-step doping process, minimizing issues such as volatilization, encapsulation, and powder agglomeration. During the heating and holding stage, a specific placement method is used to reduce volatilization and control the doping depth. Simultaneously, the crucible is rotated and adjusted during the holding and crystal growth processes. This method ensures the accuracy and uniformity of doping, thereby improving crystal growth efficiency and yield. According to the method of this embodiment, a tin-doped Ga2O3 single crystal with a diameter of 1 inch and a thickness of 10 mm was obtained. The crystal surface is smooth, without cracks or gas line defects, meeting the requirements of industrial production. Using the tin-doped Ga2O3 single crystal obtained by the preparation method of this invention as a core material, high-performance power devices can be manufactured, including field-effect transistors, diodes, or deep ultraviolet photodetectors.

[0077] Example 2 This embodiment provides a method for preparing tin-doped gallium oxide, which includes the following steps: Step S101: Mixing process The molar ratio of tin doping in gallium oxide was set at 1:99. Considering the easy burn-off of SnO2, the initial molar ratio of SnO2 to Ga2O3 was set at 1.1:98.9 (burn-off amount approximately 0.1% mol). 59.47 g of Ga2O3 and 0.53 g of SnO2 were weighed according to this mixing molar ratio and mixed to obtain 60 g of SnO2-Ga2O3 mixed powder. The mixed powder was placed in a ball mill jar and placed in a planetary ball mill. The ball mill speed was set to 150 rpm. Deionized water was added as the dispersion medium, and zirconia balls were used as the ball milling medium. The zirconia balls had three diameters: φ5, φ3, and φ1, with a mass ratio of 1:1:2 and a ball-to-material ratio of 2:1. The ball milling time was 5 hours to ensure uniform mixing and consistent particle size distribution of the raw materials. The ball-milled mixed powder was then dried at 80°C for 6 hours to remove moisture, resulting in a uniformly dried SnO2-Ga2O3 mixed powder.

[0078] Weigh out 20g of Ga2O3 powder for later use.

[0079] Step S102: Forming process The SnO2-Ga2O3 mixed powder obtained in the previous step was fed into a press and cold-formed using isostatic pressing. The forming pressure range was 200 MPa, and the holding pressure was 6-8 min. The resulting SnO2-Ga2O3 composite powder preform was in the shape of a disc, with a diameter of 25 mm, slightly smaller than the diameter of the crystal growth crucible. Each disc was 5 mm thick, weighed approximately 8 g, and had a density of 3.0 g / cm³. 3 The surface of the SnO2-Ga2O3 composite powder preform is trimmed to remove burrs and edge defects, in order to ensure stacking stability during the loading process and reduce thermal distortion caused by poor contact.

[0080] Step S103: Sintering process of SnO2-Ga2O3 composite sintered body The trimmed mixed powder blank was placed into a high-purity alumina crucible, ensuring a flat bottom and avoiding tilting. First, the SnO2-Ga2O3 composite powder blank was sintered at a first sintering temperature of 1400℃ at a rate of 1-5℃ / min for 30 h to remove adsorbed water, crystal water, and organic matter, and to promote initial bonding between powder particles, laying the foundation for subsequent high-temperature sintering. Then, the first-sintered raw material was pulverized, ball-milled again for 6 h, and pressed into shape again following the same procedure as step S102. Finally, the temperature was increased to a second sintering temperature of 1500℃ at a rate of 1-5℃ / min, and sintered for 18 h.

[0081] Step S104: Sintering process of gallium oxide sintered body The Ga2O3 powder prepared in step S101 was sintered by placing it separately into another high-purity alumina crucible and sintering it at 1700℃ for 36 h to obtain a gallium oxide sintered body.

[0082] Step S2: Loading process The SnO2-Ga2O3 composite sintered body obtained in step S103 and the gallium oxide sintered body obtained in step S104 are assembled in a clean environment according to actual growth requirements, and then placed sequentially into a crystal growth crucible and covered with a crucible lid. In this embodiment, the crucible size is 1 inch, and the total weight of the materials in the crucible is 80g. To reduce the volatilization of SnO2 in the sintered body during the heating process, the composite sintered body (SnO2+Ga2O3) is covered with gallium oxide sintered body (Ga2O3). The weight of the SnO2-Ga2O3 composite sintered body at the bottom is 60g, and the weight of the gallium oxide sintered body at the top is 20g. The SnO2-Ga2O3 composite sintered body is placed at the bottom as a doping source, and the pure gallium oxide sintered body is placed at the top as the growth host. The two are in close contact to ensure the stability of heat conduction and mass transfer. After loading, the crucible is sealed and sent into a single crystal furnace, ready for subsequent crystal growth.

[0083] Step S3: Crystal growth process A crucible containing the SnO2-Ga2O3 composite sintered body and the gallium oxide sintered body was placed in a crystal growth furnace. To ensure uniform doping distribution, the crucible was kept rotating during melt holding and crystal growth. First, the temperature was raised to the crystal growth temperature and held at 1790℃ for 5 hours. During this holding period, the first rotation speed was set to 10 rpm to allow the SnO2 and Ga2O3 raw materials to fully melt and reach thermal equilibrium. Then, the crystal growth stage began, with a gradient cooling process controlled at a rate of 0.5℃ / h. The second rotation speed was reduced to 1.2 rpm to minimize the impact of thermal convection on the crystal growth interface and promote continuous and stable single crystal growth.

[0084] Step S4: Cooling process After crystal growth, the crystal was first slowly cooled to below 1400℃ at a first cooling rate of 0.5-3℃ / min for directional annealing to release lattice stress and reduce dislocation density. The annealing time was 6 hours. Subsequently, it was further cooled to room temperature in an inert atmosphere at a second cooling rate of 0.5-2℃ / min to avoid thermal stress concentration that could lead to crystal cracking or micro-defects. The crystal was then removed from the crucible, yielding a tin-doped Ga2O3 single crystal with a diameter of 1 inch and a thickness of 12 mm. Testing showed that the actual doping molar ratio was very close to 1:99, indicating that the 0.1% mol burn-off setting for this sintering and crystal growth process was reasonable.

[0085] The method for preparing tin-doped gallium oxide crystals in this embodiment employs a two-step doping process, minimizing issues such as volatilization, encapsulation, and powder agglomeration. During the heating and holding stage, a specific placement method is used to reduce volatilization and control the doping depth. Simultaneously, the crucible is rotated and adjusted during the holding and crystal growth processes. This method ensures the accuracy and uniformity of doping, thereby improving crystal growth efficiency and yield. The transparent, colorless tin-doped Ga2O3 single crystal obtained according to this embodiment has a smooth surface, free from cracks and gas line defects, meeting industrial production requirements. Using the tin-doped Ga2O3 single crystal obtained by the method of this invention as a core material, high-performance power devices can be manufactured, including field-effect transistors, diodes, or deep ultraviolet photodetectors.

[0086] Example 3 This embodiment provides a method for preparing tin-doped gallium oxide, which includes the following steps: Step S101: Mixing process The molar ratio of tin doping in gallium oxide was set at 1:99. Considering the easy burn-off of SnO2, the initial molar ratio of SnO2 to Ga2O3 was set at 2:98 (burn-off amount approximately 1%mol). 342.7g of Ga2O3 and 7.3g of SnO2 were weighed according to this mixing molar ratio and mixed to obtain 350g of SnO2-Ga2O3 mixed powder. The mixed powder was placed in a ball mill jar and placed in a planetary ball mill. The ball mill speed was set to 200 rpm. Deionized water was added as the dispersion medium, and zirconia balls with three diameters (φ5, φ3, and φ1) were used as the milling medium. The mass ratio of the three zirconia balls was 1:1:2, the ball-to-powder ratio was 2:1, and the milling time was 10 h to ensure uniform mixing and consistent particle size distribution. The milled mixed powder was then dried at 80℃ for 6 h to remove moisture, resulting in uniformly dried SnO2-Ga2O3 mixed powder.

[0087] Weigh out 100g of Ga2O3 powder for later use.

[0088] Step S102: Forming process The SnO2-Ga2O3 mixed powder obtained in the previous step was fed into a press and cold-formed using isostatic pressing. The forming pressure range was 300 MPa, and the holding pressure was maintained for 3-6 min. The resulting SnO2-Ga2O3 composite powder preform was in the shape of a disc, with a diameter of 50 mm, slightly smaller than the diameter of the crystal growth crucible. Each disc was 8.6 mm thick, weighed approximately 50 g, and had a density of approximately 3.0 g / cm³. 3 The surface of the SnO2-Ga2O3 composite powder preform is trimmed to remove burrs and edge defects, in order to ensure stacking stability during the loading process and reduce thermal distortion caused by poor contact.

[0089] Step S103: Sintering process of SnO2-Ga2O3 composite sintered body The trimmed mixed powder blank was placed into a high-purity alumina crucible, ensuring a flat bottom and avoiding tilting. First, the SnO2-Ga2O3 composite powder blank was sintered for 30 hours at a first sintering temperature of 1485℃ at a rate of 3-5℃ / min. This removed impurities such as adsorbed water, crystal water, and organic matter from the powder and promoted initial bonding between powder particles, laying the foundation for subsequent high-temperature sintering. Then, the raw material from the first sintering was pulverized, ball-milled again for 10 hours, and pressed into shape again following the same procedure as step S102. Finally, the temperature was increased to a second sintering temperature of 1550℃ at a rate of 3-5℃ / min, and sintered for 48 hours.

[0090] Step S104: Sintering process of gallium oxide sintered body The Ga2O3 powder prepared in step S101 was sintered by placing it separately into another high-purity alumina crucible and sintering it at 1700℃ for 36 h to obtain a gallium oxide sintered body.

[0091] Step S2: Loading process The SnO2-Ga2O3 composite sintered body obtained in step S103 and the gallium oxide sintered body obtained in step S104 are assembled in a clean environment according to actual growth requirements, and then placed sequentially into a crystal growth crucible and covered with a crucible lid. In this embodiment, the crucible size is 2 inches, and the total weight of the materials in the crucible is 450g. To reduce the volatilization of SnO2 in the sintered body during the heating process, the composite sintered body (SnO2-Ga2O3) is covered with gallium oxide sintered body. The weight of the SnO2-Ga2O3 composite sintered body at the bottom is 350g, and the weight of the gallium oxide sintered body at the top is 100g. The SnO2-Ga2O3 composite sintered body is placed at the bottom as a doping source, and the pure gallium oxide sintered body is placed at the top as the growth host. The two are in close contact to ensure the stability of heat conduction and mass transfer. After loading, the crucible is sealed and sent into a single crystal furnace, ready for subsequent crystal growth.

[0092] Step S3: Crystal growth process A crucible containing the SnO2-Ga2O3 composite sintered body and the gallium oxide sintered body was placed in a crystal growth furnace. To ensure uniform doping distribution, the crucible was kept rotating during melt holding and crystal growth. First, the temperature was raised to the crystal growth temperature and held at 1815℃ for 5 hours. During this holding period, the first rotation speed was set to 12 rpm to allow the SnO2 and Ga2O3 raw materials to fully melt and reach thermal equilibrium. Then, the crystal growth stage began, with a gradient cooling process controlled at a cooling rate of 1℃ / h. The second rotation speed was reduced to 3.6 rpm to minimize the impact of thermal convection on the crystal growth interface and promote continuous and stable single crystal growth.

[0093] Step S4: Cooling process After crystal growth, the temperature was first slowly reduced to 1200℃-1400℃ at a first cooling rate of 1-3℃ / min for directional annealing to release lattice stress and reduce dislocation density. The annealing time was 8 hours. Subsequently, cooling continued to room temperature at a second cooling rate of 1-2℃ / min to avoid thermal stress concentration that could lead to crystal cracking or micro-defects. The crystal was then removed from the crucible, yielding a tin-doped Ga₂O₃ single crystal with a diameter of 2 inches and a thickness of 22 mm. Testing showed that the actual doping molar ratio was very close to 1:99, indicating that the 1% mol burn-off setting in this sintering and crystal growth process was reasonable.

[0094] The method for preparing tin-doped gallium oxide crystals in this embodiment employs a two-step doping process, minimizing issues such as volatilization, encapsulation, and powder agglomeration. During the heating and holding stage, a specific placement method is used to reduce volatilization and control the doping depth. Simultaneously, the crucible is rotated and adjusted during the holding and crystal growth processes. This method ensures the accuracy and uniformity of doping, thereby improving crystal growth efficiency and yield. The transparent, colorless tin-doped Ga2O3 single crystal obtained according to this embodiment has a smooth surface, free from cracks and gas line defects, meeting industrial production requirements. Using the tin-doped Ga2O3 single crystal obtained by the method of this invention as a core material, high-performance power devices can be manufactured, including field-effect transistors, diodes, or deep ultraviolet photodetectors.

[0095] Example 4 Example 4 is similar to Example 1, except for adjustments to the segmented sintering process steps and parameters. The segmented sintering in Example 4 includes four sintering stages to achieve gradient pre-sintering treatment of the raw materials. The specific implementation method is as follows: The trimmed mixed powder blank obtained in step S102 is placed into a high-purity alumina crucible, ensuring a flat bottom and avoiding tilting. First, the temperature is raised to the first sintering stage and held at 600-800℃ for 2-4 hours to remove adsorbed water and organic matter, preventing bubbles or cracks from forming during subsequent melting. Then, the temperature is raised to the second sintering stage and held at 1000-1200℃ for 3-5 hours to promote the formation of a uniform solid solution phase. Next, the furnace temperature is raised to 1450-1485℃ and held for 15-20 hours to facilitate the diffusion and homogenization of dopants. Finally, in the fourth sintering stage, the temperature is raised to 1500-1550℃ and held for at least 24 hours for high-temperature sintering, promoting sufficient densification between particles and grain growth to form a high-density, low-defect polycrystalline SnO2-Ga2O3 ceramic body. The heating rate at each stage is controlled at 1-5℃ / min to avoid powder agglomeration or uneven reaction due to thermal shock.

[0096] Example 5 Example 5 is similar to Example 2, except for the adjustment of the segmented sintering process steps and process parameters. Step S4 of Example 5, the cooling process, is a gradient cooling process. By precisely controlling the cooling rate, the solid-liquid interface is guided to advance smoothly, suppressing radial component segregation. The specific implementation method is as follows: After growth, the crystal is first slowly cooled to 1200-1400℃ at a first cooling rate of 0.5-3℃ / min for directional annealing to release lattice stress and reduce dislocation density. The annealing time is 9 hours. Then, it is further cooled to 800℃ at a second cooling rate of 0.5-2℃ / min to further repair point defects and dislocations generated during growth and improve the integrity of the single crystal. It is then allowed to cool naturally to room temperature in the furnace to obtain a tin-doped Ga₂O₃ single crystal with a diameter ≥ 1 inch and a thickness ≥ 10 mm. The crystal surface is smooth and free of cracks and gas line defects. The annealing process is preferably carried out in an oxygen atmosphere to compensate for oxygen vacancies that may occur at high temperatures and maintain the stable valence state of Ga in the lattice.

[0097] Example 6 Example 6 is similar to Example 3, except for the adjustment of the process parameters for the crystal growth process. The specific implementation method is as follows: In step S3 of Example 6, a back-reflective heat shield is introduced to optimize the axial temperature gradient, reduce thermal disturbance at the crystal growth interface, and thus improve crystal quality and interface stability. The heat shield is located on the outer side of the crucible bottom, aligned with the end of the heater, and is made of high-purity zirconia with a thickness of 2-5 mm. High-purity zirconia possesses excellent high-temperature resistance and low thermal radiation absorption rate, maintaining stable thermal performance during long-term operation, further ensuring the uniformity and controllability of the crystal growth environment. The heat shield effectively suppresses downward heat loss, enhancing the uniformity of the axial temperature gradient. By adjusting the relative position of the heat shield and the heating zone, the shape and position of the crystal growth interface can be precisely controlled, promoting planar interface growth, thereby reducing the probability of grain boundary and twin formation and improving the stability and repeatability of single crystal growth. Simultaneously, this structure reduces temperature fluctuations at the bottom of the crucible, avoiding localized overcooling or recrystallization of the melt, significantly improving the continuity and integrity of crystal growth.

[0098] By introducing a heat shield, the growth rate stability of gallium oxide crystals is improved by approximately 18%, and the radial temperature difference is controlled within ±2℃. The resulting tin-doped Ga2O3 single crystals have a diameter ≥2 inches and a thickness ≥20 mm, with the oxygen vacancy concentration in the single crystal reduced by an order of magnitude. The crystal surface is smooth and free of cracks and gas line defects. This meets the requirements of high-end power devices for high-purity and high-uniformity semiconductor materials.

[0099] Comparative Example 1 To further verify the effectiveness of this embodiment, the inventors designed Comparative Example 1 for comparative experiments. In Comparative Example 1, a one-step sintering method was used, with a sintering regime of 1600℃ for 36 hours. Other processes and regimes were the same as in Example 1. Finally, the highest tin doping concentration in the gallium oxide crystal was 0.2%, and localized compositional inhomogeneity was observed.

[0100] Comparative Example 2 In Comparative Example 2, a two-step sintering method was used, but the composite sintered block was placed on top of the gallium oxide sintered block; the other processes and procedures were the same as in Example 2. Finally, the highest tin doping concentration in the gallium oxide crystal was 0.55%, and localized compositional inhomogeneity was observed.

[0101] Comparative Example 3 In Comparative Example 3, a two-step sintering method was used, and the composite sintered block was placed below the gallium oxide sintered block. However, the crucible was not rotated during the crystal holding and growth process, and the other processes and procedures were the same as in Example 2. Finally, tin doping in the gallium oxide crystal showed a layering phenomenon.

[0102] Comparative Example 4 In Comparative Example 4, the crucible rotated at a relatively high speed of 20 rpm during crystal growth, while other steps and procedures were consistent with those in Example 3. The SnO2 concentration in the grown gallium oxide crystal gradually increased from the center to the edge.

[0103] In summary, the tin-doped Ga2O3 single crystal preparation method provided in this application forms a complete and effective tin doping technology solution through stepwise sintering, specific sintered body placement, crucible rotation control, and segmented cooling. By precisely controlling the conditions and parameters of each process, uniform distribution of doping elements in the gallium oxide melt is achieved, resulting in a more precise doping ratio and a more stable doping effect. This further improves the overall performance of β-Ga2O3 single crystal materials and provides a strong guarantee for the preparation of high-quality gallium oxide single crystals. Furthermore, by controlling the rotational equal-growth crystal process parameters, this invention ensures the consistency of substrate doping concentration, which is crucial for the large-scale production and development of single crystal substrates.

[0104] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this application may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0105] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features but not others included in other embodiments, combinations of features from different embodiments are meant to be within the scope of the embodiments of this application and form different embodiments. For example, in the following claims, any one of the claimed embodiments can be used in any combination.

Claims

1. A method for preparing a tin-doped gallium oxide single crystal material, characterized in that, The method includes the following steps: Step S1: Sintering process, SnO2 and Ga2O3 powders are mixed according to stoichiometric ratio, sintered once at a first sintering temperature, and then sintered a second time at a higher second sintering temperature to obtain a SnO2-Ga2O3 composite sintered body; the first and second sintering temperatures are both below 1600℃; Ga2O3 is sintered once to obtain a Ga2O3 sintered body; Step S2: Loading process. The SnO2-Ga2O3 composite sintered body and the pure Ga2O3 sintered body are assembled in the crystal growth crucible according to the growth requirements to form a layered filler structure. First, the SnO2-Ga2O3 composite sintered body is placed in the crucible, and then the gallium oxide sintered body is placed on top and the crucible lid is closed. Step S3: Crystal growth process. The crucible containing the SnO2-Ga2O3 composite sintered body and the gallium oxide sintered body is placed in the crystal growth furnace. The temperature is raised to the crystal growth temperature range of 1750-1820℃ and held within this temperature range for 3-5 hours. During the holding process, the first rotation speed of the crucible is set to ensure that SnO2 and Ga2O3 are fully fused. Subsequently, during the crystal growth process, the second rotation speed of the crucible is reduced to promote continuous and stable growth of single crystals. Step S4: Cooling process. After crystal growth, a segmented cooling method is adopted. First, the temperature is slowly reduced to below 1400°C at the first cooling rate, and the annealing time is 6-12 hours. Then, the temperature is slowly reduced to 800°C at the second cooling rate. After that, the temperature is naturally cooled to room temperature in the furnace. The tin-doped gallium oxide single crystal is taken out from the crucible. The second cooling rate is less than or equal to the first cooling rate.

2. The method for preparing a tin-doped gallium oxide single crystal material according to claim 1, characterized in that, Step S1 also includes the following sub-steps: Step S101: Mixing process, high-purity Ga2O3 powder and SnO2 dopant are mixed according to a predetermined stoichiometric ratio, and the amount of SnO2 added is the sum of the expected doping amount and the volatilization compensation amount. Ball milling is performed to ensure that the raw materials are fully and uniformly mixed; weigh the Ga2O3 powder for later use. Step S102: Forming process, the mixed powder obtained after ball milling is fed into a press and cold-formed by isostatic pressing or unidirectional pressing to obtain a mixed powder blank with uniform density. The shape and size of the mixed powder blank are matched with the inner cavity of the crucible. Step S103: Sintering process of SnO2-Ga2O3 composite sintered body: The trimmed mixed powder blank is loaded into a high-purity alumina crucible, first heated to the first heating temperature, and sintered once for the first sintering time. Then the raw material obtained from the first sintering is crushed, ball-milled again and pressed into shape, and then heated to the second heating temperature and sintered a second time for the second sintering time. Step S104: Sintering process of Ga2O3 sintered body. The Ga2O3 powder weighed in step S101 is separately loaded into another high-purity alumina crucible and sintered at a temperature range of 1650-1700℃ for more than 24 hours to obtain a dense pure Ga2O3 sintered body.

3. The method for preparing a tin-doped gallium oxide single crystal material according to claim 2, characterized in that, In step S104, sintering is carried out at a temperature range of 1650-1700℃ for more than 36 hours to obtain a dense pure Ga2O3 sintered body.

4. A method for preparing a tin-doped gallium oxide single crystal material according to any one of claims 2 to 3, characterized in that, In step S1 or step S101, the expected doping amount of the SnO2 dopant is 1:99, and the volatilization compensation amount is 10% to 50% of the expected doping amount to offset the volatilization loss of Sn element during high-temperature growth; the stoichiometric ratio of the SnO2 dopant to the Ga2O3 powder is 1.1:98.

9.

5. The method for preparing a tin-doped gallium oxide single crystal material according to claim 4, characterized in that, The stoichiometric ratio of the SnO2 dopant to the Ga2O3 powder is 1.5:98.

5.

6. The method for preparing a tin-doped gallium oxide single crystal material according to claim 4, characterized in that, The stoichiometric ratio of the SnO2 dopant to the Ga2O3 powder is 1.8:98.

2.

7. The method for preparing a tin-doped gallium oxide single crystal material according to claim 4, characterized in that, The stoichiometric ratio of the SnO2 dopant to the Ga2O3 powder is 2:

98.

8. A method for preparing a tin-doped gallium oxide single crystal material according to any one of claims 1 to 3, characterized in that, In step S1 or step S103, the first sintering temperature is in the range of 1400-1500℃, and the first sintering time is more than 2 hours; the second sintering temperature is in the range of 1500-1580℃, and the second sintering time is more than 18 hours.

9. A method for preparing a tin-doped gallium oxide single crystal material according to claim 2, characterized in that, In step S102, the pressing pressure is controlled between 100-300 MPa, and the pressure is held for 3-10 min; the thickness of the mixed powder preform is about 5-15 mm.

10. A method for preparing a tin-doped gallium oxide single crystal material according to claim 1, characterized in that, In step S3, the first rotational speed is 5-20 rpm, and the second rotational speed is reduced to 1-4 rpm.

11. The method for preparing a tin-doped gallium oxide single crystal material according to claim 1, characterized in that, In step S3, a back reflective heat insulation screen is introduced to optimize the axial temperature gradient and reduce thermal disturbance at the crystal growth interface. The reflective screen material is a high-purity zirconium oxide structure.

12. The method for preparing a tin-doped gallium oxide single crystal material according to claim 1, characterized in that, Step S1 includes three heating stages to form a SnO2-Ga2O3 composite sintered body.

13. The method for preparing a tin-doped gallium oxide single crystal material according to claim 1, characterized in that, Step S1 includes multiple heating stages. The first heating stage raises the temperature to 600-800℃ to remove adsorbed water and organic matter. The second heating stage raises the temperature to 1000-1200℃ to promote the initial reaction of the precursor. The third stage raises the furnace temperature to 1400-1485℃ to initially form a solid solution phase and eliminate local concentration gradients. The fourth stage continues to raise the temperature to 1500-1550℃ to promote sufficient densification between particles and grain growth, forming a SnO2-Ga2O3 composite sintered body.

14. A tin-doped Ga2O3 single crystal, characterized in that, The tin-doped Ga2O3 single crystal is prepared by the method according to any one of claims 1-13, wherein the tin doping molar ratio in the tin-doped Ga2O3 single crystal is about 1:99, and the tin burn-off rate is 10% to 50%.

15. A power device based on the tin-doped Ga2O3 single crystal, characterized in that, The power device uses tin-doped Ga2O3 single crystal as described in claim 14 as the core material, including field-effect transistors, diodes, or deep ultraviolet light detectors.

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