Low-Temperature and Rapid Oxidation of GaN Surface by Saturated Water Vapor at High Pressure

A gallium oxide layer was successfully formed on a GaN surface by saturated water vapor oxidation at a high pressure (350 °C, 16.5 MPa). Ga oxide thickness can be controlled in the 5–1,000 nm range by such oxidation process for 15 min. Saturated water vapor oxidation is a rapid and very low temperature oxidation process compared with the conventional thermal oxidation of GaN. This rapid oxidation potential at a low temperature is attributed to the high density of the oxidizer (H2O) under high-pressure condition. By applying post-treatment with high-pressure hot water, residual nitrogen in the oxide layer is removed and the stoichiometric composition of Ga2O3 is observed by X-ray photoelectron spectroscopy (XPS). The removal of nitrogen from the oxide by the high-pressure hot water is caused by its high solubility of inorganic compounds. Rapid and low-temperature oxidation can be applicable to the fabrication of a high-performance device without thermal stress for GaN-field effect transistors (FETs).