Heteroepitaxial Growth of Ga <sub>2</sub> O <sub>3</sub> Thin Films of Various Phase Composition by Oxidation of Ga in Hydrogen-Oxygen Plasmas
Leonid Mochalov, Alexander Logunov, Mikhail Kudryashov, I. O. Prokhorov, Tatiana Sazanova, P. A. Yunin, V. I. Pryakhina, Ilya Vorotuntsev, В. М. Малышев, A. Y. Polyakov, S. J. Pearton
Abstract
We describe a novel plasma-chemical method for Ga 2 O 3 thin films synthesis, in which high-purity elemental Ga is delivered by hydrogen flow into the plasma discharge zone to react with O 2 . Radio Frequency (40 MHz) non-equilibrium low temperature plasma discharge at low pressure (0.01 Torr) is applied for initiation of interaction between these precursors. Optical Emission Spectroscopy together with quantum-chemical calculations was used to determine the main reaction pathways and reacting species appearing in the plasma discharge. For a low growth temperature of 350 °C and high plasma power of 50 W, the Ga 2 O 3 films deposited on basal plane sapphire are textured β -Ga 2 O 3 with (−201) orientation. At low plasma power of 30 W and low growth temperature of 350 °C, the layers are dominated by the polycrystalline ε (k) phase. Increasing the growth temperature under these low plasma power conditions from 350 °C to 550 °C leads to the grains ripening and the conversion of the films into the polycrystalline β -polytype. Electrical measurements on the films grown under high power conditions on sapphire showed them to be semi-insulating, with the Fermi level pinned near E c −0.7 eV. Films on Si substrates had low donor concentrations of ∼10 15 cm −3 , most likely due to Si autodoping from the Si substrate.