The adsorption of oxygen at GaN surfaces

A critical point in device fabrication based on GaN is the controlled doping and the incorporation of impurities like, e.g., oxygen. We have explored the adsorption of oxygen at the wurtzite (0001) and $\text{(0001̄)}$ GaN surfaces employing density-functional theory. Our results show that both surface orientations are very active towards oxygen adsorption, explaining the high oxygen concentrations typically observed in GaN. However, the (0001) and $\text{(0001̄)}$ surfaces behave differently and oxygen incorporation is expected to be higher at the $\text{(0001̄)}$ surface. The different reactivity is explained in terms of the specific structural configurations.