【Member Papers】Liquid-metal-printed buffer layer enabling offcut-tolerant MOCVD heteroepitaxy of β-Ga₂O₃ on sapphire

      Researchers from Chaozhou Branch of Chemistry and Chemical Engineering Guangdong Laboratory and JFS Laboratory have published a dissertation titled " Liquid-metal printed buffer layer enabling offcut-tolerant MOCVD heteroepitaxy of β-Ga₂O₃ on sapphire " in Journal of Alloys and Compounds.

Background

      Monoclinic gallium oxide (β-Ga₂O₃₎ has garnered significant attention as an ultra-wide-bandgap semiconductor for next-generation power electronics and solar-blind ultraviolet optoelectronics. The heteroepitaxial growth of β-Ga₂O₃ via metalorganic chemical vapor deposition (MOCVD) represents critical fabrication strategy for producing high-quality films with well-defined band structures and electrical properties. Neverthless, achieving uniform and reproducible epitaxy on foreign substrates presents fundamentally challenging. This difficulty arises from the highly sensitive of heteroepitaxy to the initial interfacial conditions established during the earliest stages of nucleation. Specifically, substrate surface geometry defined by surface atomic steps and local bonding environments, collectively dictate growth mode selection and defect formation. In of the context of β-Ga₂O₃ heteroepitaxy, this sensitivity is further exacerbated by variations in substrate offcut angles, which influence step-flow dynamics. Consequently, these variarions lead to inconsistent nucleation behavior, variable crystalline quality, and limited process reproducibility.

Abstract

      Heteroepitaxial growth of β-Ga₂O₃ is typically constrained by a pronounced sensitivity to substrate offcut angles, which dictates surface step dynamics and nucleation behavior, thereby limiting film uniformity and reproducibility. Herein, we report an interface-engineering strategy utilizing a liquid-metal-printed Ga₂O₃ buffer layer that employs a structurally reconfigurable precursor. Upon thermal oxidation and controlled crystallization, this ultrathin buffer effectively reconstructs the interfacial conditions and governs the early stages of epitaxy, thereby providing a quasi-homoepitaxial template for subsequent metalorganic chemical vapor deposition (MOCVD) growth of β-Ga₂O₃ films. Significantly, the buffer layer enables the growth of β-Ga₂O₃ films with systematically improved crystalline coherence, reduced surface roughness, and enhanced morphological uniformity across sapphire substrates with offcut angles ranging from 0° to 6°. This interface-engineering effect significantly mitigates the constraint imposed by substrate geometry, resulting in markedly improved process tolerance. This work underscores the effectiveness of liquid-metal-printed buffer layers as reconfigurable interface precursors for regulating epitaxial growth sensitivity, offering a low-cost and scalable method to alleviate substrate geometry constraints. It establishes a robust paradigm for high quality β-Ga₂O₃ heteroepitaxy on sapphire, contributing to advancements in electronic and optoelectronic material platforms.

Conclusion

      In summary, this work demonstrates a liquid-metal-printed Ga₂O₃ buffer layer strategy for regulating MOCVD heteroepitaxy of β-Ga₂O₃ on sapphire substrates. By introducing a reconfigurable interfacial precursor, the printed Ga₂O₃ buffer layer effectively modifies the early-stage growth conditions, enabling strain accommodation and, more importantly, homogenization of the nucleation environment. This fundamentally weakens the stringent substrate orientation selectivity inherent to conventional epitaxy. Consequently, exceptional film properties including a narrow X-ray rocking curve FWHM of approximately 1.1°-1.2°, a low RMS roughness below 3 nm, and a markedly reduced concentration of oxygen-vacancy-related defects are consistently achieved across the entire range of substrate offcut angles studied. This approach relaxes the stringent requirements on substrate orientation in conventional heteroepitaxy, thereby improving process tolerance and reproducibility. Beyond β-Ga₂O₃, the printed-buffer-mediated growth decoupling strategy may also might provide a versatile interface-engineering route for achieving robust heteroepitaxy of wide-bandgap semiconductors on non-native substrates.

Project Support

      This work was supported by the Chaozhou City Ceramics Industry Talent Revitalization Plan Project (GXYJ001) and the National Natural Science Foundation of China (No. 52472072 & No. 52502075). The authors would like to acknowledge the support of Major Program (JD) of Hubei Province (2023BAA009), and JFS Laboratory.