Thermal stability of epitaxial α-Ga2O3 and (Al,Ga)2O3 layers on m-plane sapphire.

Here, we have explored the thermal stability of α-(Al,Ga)₂O₃ grown by the molecular-beam epitaxy on m-plane sapphire under high-temperature annealing conditions for various Al compositions (i.e., 0%, 46%, and 100%). Though uncapped α-Ga₂O₃ undergoes a structural phase transition to the thermodynamically stable β-phase at high temperatures, we find that an aluminum oxide cap grown by atomic layer deposition preserves the α-phase. Unlike uncapped α-Ga₂O₃, uncapped α-(Al,Ga)₂O₃ at 46% and 100% Al content remain stable at high temperatures. We quantify the evolution of the structural properties of α-Ga₂O₃, α-(Al,Ga)₂O₃, and α-Al₂O₃ and the energy bandgap of α-Ga₂O₃ up to 900 °C. Throughout the anneals, the α-Ga₂O₃ capped with aluminum oxide retains its high crystal quality, with no substantial roughening. [ABSTRACT FROM AUTHOR]