Nano-scale Al redistribution at grain boundaries governs growth morphology in β-(Al_xGa_1-x)₂O₃ on sapphire substrate...

Ultra-wide-bandgap β-Ga₂O₃ is a promising platform for next-generation deep-UV optoelectronics and high-power electronics. Here, we report controlled growth of β-(Al_xGa_1-x)₂O₃ epilayers on sapphire by metalorganic chemical vapor deposition with tunable trimethylaluminum supply (2.24 × 10^-6-3.36 × 10^-5 mol min^-1). Systematic X-ray diffraction peak shifts toward higher angles confirm progressive Al incorporation and lattice contraction, while cross-sectional microscopy reveals an increase in film thickness from 153 to 278 nm, indicating enhanced nucleation and growth kinetics. Optical spectroscopy demonstrates tunable bandgaps from 4.92 to 5.66 eV, and Vegard's-law analysis quantifies Al contents of ~ 6-36%. Atomic-resolution STEM combined with first-principles calculations reveals nano-scale Al redistribution and demonstrates that Al incorporation significantly lowers the surface energy of the O-terminated (100) facet, promoting lateral growth and yielding characteristic rectangular platelet morphologies. These results establish a quantitative thermodynamic origin for morphology control in β-(Al_xGa_1-x)₂O₃ and provide a framework for morphology-engineered ultra-wide-bandgap oxide electronics.