Atomic-Scale Insight into Epitaxial Growth and Defect Structures of Metastable α-Ga ₂ O ₃ Thin Films

Metastable α-Ga2O3 possesses a wider bandgap and higher symmetry compared to the stable β-phase, making it a premier candidate for next-generation power electronics and deep ultraviolet optoelectronics. However, achieving pure-phase epitaxy and understanding the nanoscale defect evolution remain significant challenges. Here, we report the high-crystallinity growth of pure α-Ga2O3 thin films on (112̅0) Al2O3 substrates via pulsed laser deposition. By systematically tailoring the growth temperature (600–800 °C) and O2 partial pressure (0.01–10 Pa), we identified 750 °C and 5 Pa as the optimal parameters for growing α-Ga2O3 thin films. Aberration-corrected scanning transmission electron microscopy reveals that an atomically flat and coherent interface is formed between α-Ga2O3 and Al2O3, characterized by direct Ga–O bonding without elemental diffusion. A high-density network of stacking faults (SFs) was formed in the α-Ga2O3 thin film. It revealed that the basal-plane SFs have sharp interfaces, and the faults are caused by the relative sliding between Ga and O atomic layers along the (0001) plane. Our findings provide critical atomic-scale insights into the structural engineering of corundum-structured oxides for advanced semiconductor applications.