Thermal Stability Of Epitaxial Alpha-Ga2o3 And (Al,Ga)(2)O-3 Layers On M-Plane Sapphire

Here, we have explored the thermal stability of alpha-(Al,Ga)(2)O-3 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 alpha-Ga2O3 undergoes a structural phase transition to the thermodynamically stable beta-phase at high temperatures, we find that an aluminum oxide cap grown by atomic layer deposition preserves the alpha-phase. Unlike uncapped alpha-Ga2O3, uncapped alpha-(Al,Ga)(2)O-3 at 46% and 100% Al content remain stable at high temperatures. We quantify the evolution of the structural properties of alpha-Ga2O3, alpha-(Al,Ga)(2)O-3, and alpha-Al2O3 and the energy bandgap of alpha-Ga2O3 up to 900 degrees C. Throughout the anneals, the alpha-Ga2O3 capped with aluminum oxide retains its high crystal quality, with no substantial roughening.