Epitaxial undoped indium oxide thin films: Structural and physical properties

Indium oxide thin films were grown by the pulsed electron beam deposition method on c-cut sapphire substrates at 10−2 mbar oxygen pressure and temperature up to 500 °C. Such conditions lead to the formation of dense, smooth and stoichiometric In2O3 films, with the cubic bixbyite structure. Epitaxial thin films were obtained at substrate temperatures as low as 200 °C. Pole figure measurements indicate the existence of (111) oriented In2O3 crystallites with different in-plane symmetry, i.e. three-fold and six-fold symmetry. The origin of this effect may be related to the specificities of the growth method which can induce a large disorder in the oxygen network of In2O3, leading then to a six-fold symmetry in the (111) plane of the bixbyite structure. This temperature resistivity behaviour shows metallic conductivity at room temperature and a metal-semiconductor transition at low temperature for In2O3 films grown at 200 °C, while the classical semiconductor behaviour was observed for the films grown at 400 and 500 °C. A maximum mobility of 24.7 cm2/V s was measured at 200 °C, and then it falls off with improving the crystalline quality of films. The optical transparency is high (>80%) in a spectral range from 500 nm to 900 nm.