Thermal stability of epitaxial <i>α</i>-Ga2O3 and (Al,Ga)2O3 layers on m-plane sapphire
Jonathan P. McCandless, Celesta S. Chang, Kazuki Nomoto, Joseph Casamento, Vladimir Protasenko, Patrick Vogt, Derek Rowe, Katie R. Gann, Shao-Ting Ho, Wenshen Li, Riena Jinno, Yong-Jin Cho, A. J. Green, Kelson D. Chabak, Darrell G. Schlom, Michael O. Thompson, David A. Muller, Huili Grace Xing, Debdeep Jena
Abstract
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.