Crystal orientation of β-Ga2O3 thin films formed on c-plane and a-plane sapphire substrate

beta-Ga2O3 thin films were prepared by gallium evaporation in oxygen plasma. The crystal orientation of the beta-Ga2O3 films was studied in detail using X-ray diffraction, pole figure measurements and analysis using a crystal model. beta-Ga2O3 films formed on both the (001) c-plane and (110) a-plane of the sapphire substrate were found to be strongly ((2) over tilde 01) oriented. Six crystal types of beta-Ga2O3 are formed, rotated about the [(2) over bar 01] direction. The six directions depend on the arrangement of oxygen on the surface of the sapphire substrate. The direction of [201] of beta-Ga2O3 is vertical to the sapphire {100} planes. The arrangement of oxygen on the (001) c-plane sapphire substrate is equivalent to that formed on the ((2) over bar 01) plane of beta-Ga2O3 due to a small mismatch in the spacing between oxygen atoms. This mismatch explains why beta-Ga2O3 is ((2) over bar 01) oriented on the (001) c-plane sapphire substrate. (C) 2012 Elsevier B.V. All rights reserved.