Wet thermal oxidation of GaN

Thermal oxidation of GaN was conducted at 700-900 degrees C with O-2, N-2, and Ar as carrier gases for 525-630 Torr of H2O vapor. Upon oxidation of both GaN powders and n-GaN epilayers, the monoclinic beta-Ga2O3 phase was identified using glancing angle x-ray diffraction. The chemical composition of the oxide was verified using x-ray photoelectron spectroscopy. In experiments conducted using GaN powder, the oxide grew most rapidly when O-2 was the carrier gas for H2O. The same result was obtained on n-type GaN epilayers. Furthermore, the thickness of the oxide grown in H2O with O-2 as the carrier gas was found to be proportional to the oxidation time at all temperatures studied, and an activation energy of 210+/-10 kJ/mol was obtained. Scanning electron microscopy revealed a smoother surface after wet oxidation than was reported previously for dry oxidation. However, cross-sectional transmission electron microscopy revealed that the wet oxide/GaN interface was irregular and non-ideal for device fabrication, even more so than the dry oxide/GaN interface. This observation was consistent with poor electrical properties.