Heteroepitaxial Growth of Ga2O3 Thin Films of Various Phase Composition by Oxidation of Ga in Hydrogen-Oxygen Plasmas

Abstract

We describe a novel plasma-chemical method for Ga2O3 thin films synthesis, in which high-purity elemental Ga is delivered by hydrogen flow into the plasma discharge zone to react with O2. 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 Ga2O3 films deposited on basal plane sapphire are textured β-Ga2O3 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 Ec−0.7 eV. Films on Si substrates had low donor concentrations of ∼1015 cm−3, most likely due to Si autodoping from the Si substrate.