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

β-Ga2O3 thin films were prepared by gallium evaporation in oxygen plasma. The crystal orientation of the β-Ga2O3 films was studied in detail using X-ray diffraction, pole figure measurements and analysis using a crystal model. β-Ga2O3 films formed on both the (001) c-plane and (110) a-plane of the sapphire substrate were found to be strongly (2̄01) oriented. Six crystal types of β-Ga2O3 are formed, rotated about the [2̄01] direction. The six directions depend on the arrangement of oxygen on the surface of the sapphire substrate. The direction of [201] of β-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 (2̄01) plane of β-Ga2O3 due to a small mismatch in the spacing between oxygen atoms. This mismatch explains why β-Ga2O3 is (2̄01) oriented on the (001) c-plane sapphire substrate.