Heteroepitaxial Growth of β ‐Ga ₂ O ₃ on Diamond (111) via Radio Frequency Magnetron Sputtering: Mechanistic Insights from Scanning/Transmission Electron Microscopy

Abstract This study delves into the comprehensive microstructural analysis of heteroepitaxial β ‐Ga ₂ O ₃ thin films grown on single‐crystal diamond (111) wafers by radio frequency magnetron sputtering. The heterostructure is probed through a scanning/transmission electron microscope and succeeded in direct observation of β ‐Ga ₂ O ₃ <010>||diamond [10] and β ‐Ga ₂ O ₃ <132>||diamond [10] heteroepitaxial interfaces, which up to now have only has been inferred through indirect analyzing methods based on X‐ray diffraction. Fast Fourier Transformation (FFT) patterns of corresponding oriented interfaces exhibited virtual overlapping for the substrate and the epilayer, authenticating the robust epitaxial arrangement. Furthermore, this study elucidates the discrete growth modes of β ‐Ga ₂ O ₃ <010> and <132> domains arising from the asymmetric hexagonal C─O lattice matching, through 4D‐STEM analysis and subsequent virtual dark‐field image reconstruction. Strategies for the improvement of crystallinity, surface morphology, and facile thickness controllability of the β‐Ga ₂ O ₃ epilayer through optimizing the RF power, facilitating a low re‐evaporation rate of the film, are discussed. This finding underscores the importance of domain control in the improved epitaxial quality of β ‐Ga ₂ O ₃ that can inform the development of budget‐friendly and scalable β ‐Ga ₂ O ₃ /diamond heterostructures for advanced functional devices.