Thermal oxidation of [0001] GaN in water vapor compared with dry and wet oxidation: Oxide properties and impact on GaN

[Display omitted] •Dry oxidation of GaN creates the thickest and grainiest of oxides.•Addition of water vapor to the process reduces the graininess, however, the grains are still present.•Oxide formed in the water vapor mode is thin, featureless, and conformal to the GaN surface.•Negligible oxygen diffusion into GaN was observed for the vapor mode compared to significant diffusion observed for the dry and wet modes.•Optical studies confirm that only the vapor mode has no or negligible impact on the GaN quality; the other two modes degrade the material significantly. Conventionally thermal oxidation of GaN is performed in either dry or wet oxygen ambient. In this work thermal oxidation in water vapor ambient, together with the two above mentioned modes, is characterized. All three GaN oxidation modes were comprehensively studied structurally and optically using a wide range of experimental methods. Thermal oxidation of GaN at 950 °C in dry oxygen, in wet oxygen, and in water vapor, was performed for up to 20 min. All oxidation modes resulted in β-phase Ga2O3 growth as confirmed by XRD measurements. A different surface morphology was observed between processes, smooth and featureless for the vapor oxidation, and grainy for dry and wet modes. Similarly, the growth rate varied between modes of oxidation with the slowest observed for the vapor mode and the fastest for the dry mode. An oxygen diffusion into GaN was observed for the dry and wet processes with above background levels of O visible over 150 nm below the oxide/GaN interface. Conversely, only negligible diffusion was observed for the vapor oxidized GaN. Optical studies of the structures electronic properties revealed that only the vapor process did not degrade the material underneath the oxide layer.