Wet thermal oxidation of GaN

Thermal oxidation of GaN was conducted at 700-900 °C with O₂, N₂, and Ar as carrier gases for 525-630 Torr of H₂O vapor. Upon oxidation of both GaN powders and n-GaN epilayers, the monoclinic β-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 O₂ 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 O₂ 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.