Crystal orientation dictated epitaxy of ultrawide-bandgap 5.4- to 8.6-eV α-(AlGa) <sub>2</sub> O <sub>3</sub> on m-plane sapphire
Riena Jinno, Celesta S. Chang, Takeyoshi Onuma, Yong-Jin Cho, Shao-Ting Ho, Derek Rowe, Michael C. Cao, Kevin Lee, Vladimir Protasenko, Darrell G. Schlom, David A. Muller, Huili Grace Xing, Debdeep Jena
Abstract
alloys spanning bandgaps of 5.4 to 8.6 eV can be grown by molecular beam epitaxy. The key step is found to be the use of m-plane sapphire crystal. The phase transition of the epitaxial layers from the α- to the narrower bandgap β-phase is catalyzed by the c-plane of the crystal. Because the c-plane is orthogonal to the growth front of the m-plane surface of the crystal, the narrower bandgap pathways are eliminated, revealing a route to much wider bandgap materials with structural purity. The resulting energy bandgaps of the epitaxial layers span a broad range, heralding the successful epitaxial stabilization of the largest bandgap materials family to date.