【Member Papers】Recent Advances in the Mist Chemical Vapor Deposition of Ga₂O₃ Thin Films

      Researchers from Wuhan University of Technology, Inner Mongolia University of Technology, Shandong Jingsheng Electronic Technology Co., Ltd, Fuzhou University and Universitas Airlangga (Indonesia) have published a paper titled "Recent Advances in the Mist Chemical Vapor Deposition of Ga₂O₃ Thin Films" in Crystal Growth & Design.

Background

      Ga₂O₃, an ultra-wide bandgap semiconductor with bandgap of 4.7–5.6 eV and an ultrahigh theoretical breakdown field up to 8 MV/cm, plays an irreplaceable role in solar-blind ultraviolet photodetectors and high-voltage power devices. Conventional epitaxy technologies including MOCVD, MBE and HVPE require vacuum chambers, leading to high equipment cost and limited large-scale mass production capacity. Mist chemical vapor deposition (mist CVD) operates under atmospheric pressure without vacuum environment, featuring low cost of apparatus and precursors as well as wide tunable solution chemistry, which serves as a promising route for low-cost scalable growth of various Ga₂O₃ polymorphs. Ga₂O₃ has five polymorphs including α, β, γ, δ, ε/κ with distinct electronic and optical anisotropic properties. However, systematic reviews focusing on precise phase control, interfacial buffer layer suppression, elimination of in-plane rotational domains and regulation of impurities/vacancies in mist CVD systems are still absent. This work comprehensively sorts out reactor configurations and growth thermodynamics/kinetics of mist CVD, summarizes research progress covering phase engineering, crystallinity & surface morphology optimization, defect/impurity management, large-area epitaxy and device applications, and analyzes industrial bottlenecks, providing complete theoretical and technical references for low-cost mass fabrication of Ga₂O₃ devices.

Abstract

      Gallium oxide (Ga₂O₃), as an emerging ultrawide bandgap semiconductor with high breakdown voltage, excellent thermal and chemical stability, has shown great potential for applications in high-voltage power devices and deep ultraviolet optoelectronic detection. To realize its practical applications, low-cost and large-scale manufacturing techniques are urgently needed. In this context, mist chemical vapor deposition (mist CVD) has emerged as an important candidate for Ga₂O₃ epitaxy, benefiting from its atmospheric-pressure, nonvacuum operation, low equipment and precursor costs, wide process window, and tunable solution chemistry. Hence, this review summarizes the configuration and deposition mechanism of mist CVD. It then systematically reviews recent research progress on the controlled epitaxy of Ga₂O₃, covering phase engineering, regulation of crystallinity and surface morphology, suppression of impurities and defects, interfacial buffer layer control, elimination of in-plane rotational domains, large-area rapid epitaxy, and corresponding device applications. The challenges and prospects of wafer-scale uniform heteroepitaxy and industrial integration are also discussed. This review systematically deconstructs existing technical bottlenecks and provides transformative insights into controllable synthesis of high-quality Ga₂O₃ epitaxial films, offering a clear roadmap toward next-generation ultra-wide bandgap semiconductor power and optoelectronic hardware based on mist CVD.

Highlights

      For the first time, this paper fully reviews the full-process thermodynamics and kinetics of mist CVD growth, compares advantages and disadvantages of three reactor types (vertical hot-wall, fine-channel, linear-source), and systematically illustrates the core Leidenfrost droplet growth mechanism;

      It comprehensively summarizes controllable growth strategies of five Ga₂O₃ polymorphs (α, β, γ, δ, ε/κ) in mist CVD systems, and clarifies four core phase-control variables including temperature, substrate, doping and precursor;

      It categorizes three process routes to eliminate in-plane rotational domains including homologous/heterologous buffer layers, vicinal miscut substrates and element doping, and provides feasible approaches to obtain single-domain Ga₂O₃ thin films;

      It systematically elaborates formation mechanism and elimination methods of intrinsic oxygen vacancies and extrinsic carbon impurities, and fully compares impurity control performance of halide and acetylacetonate precursors;

      It summarizes optimization strategies for wafer-scale uniform epitaxy, sorts out performance merits and existing limitations of mist CVD-fabricated solar-blind photodetectors, Schottky power diodes and neuromorphic ferroelectric devices, and points out industrial optimization directions.

Conclusion

      In summary, mist CVD has emerged as a highly promising technique for the epitaxial growth of Ga₂O₃ thin films. Operating under atmospheric pressure without vacuum systems, it offers outstanding cost-efficiency, precursor flexibility, and scalability for industrial wafer production. Over recent years, significant progress has been made in phase-selective epitaxy of α, β, γ, δ, ε / κ polymorphs, improvement of crystalline quality and surface morphology, suppression of carbon impurities and oxygen vacancies, regulation of interfacial buffer layers and mitigation of rotational domains, as well as preliminary achievements in large-area epitaxy. These advances position mist CVD as a core candidate technology for industrial preparation of Ga₂O₃ films and provide strong support for its applications in power devices and deep-ultraviolet photodetectors. To transition mist CVD from laboratory-scale research to commercial semiconductor platforms, three core challenges must be addressed: complete elimination of carbon residue and stable controllable donor activation, realization of single-domain epitaxy on mismatched substrates via advanced substrate and buffer engineering, and development of large-size showerhead reactors for 4–6 inch wafers with uniform thickness and composition. Combined with fluid dynamic simulation and machine learning optimization, mist CVD will unlock the full potential of low-cost Ga₂O₃ electronics in high-power grids and solar-blind detection systems.

Project Support

      This work was supported by the National Natural Science Foundation of China (No. 52402200 and 52272161), Hubei Provincial Science and Technology Plan (No. 2025CSA020), and the Chaozhou City Ceramics Industry Talent Revitalization Plan Project (GXYJ001), 2024 Inner Mongolia University of Technology Strategic Priority Research Program - Mechanical Issues in New Energy Equipment and Operation (DC2400003362).