Ab initio study of oxygen point defects in GaAs, GaN, and AlN

We have studied oxygen point defects with the plane-wave pseudopotential method in GaAs, GaN, and AlN. The calculations demonstrate a qualitatively different behavior of oxygen impurities in these materials. O-As in GaAs acts as a deep center with an off-center displacement and negative-U behavior, in agreement with the experimental data. O-N in GaN is found to be a shallow donor with a low formation energy, and is suggested to act as a partial source for the unintentional n-type conductivity commonly observed in GaN. O in AlN is also found to easily substitute for N, which is consistent with the experimentally observed Inr ge oxygen concentrations in AlN. However, O-N in AlN is shows to be a deep center due to the wide band gap, in contrast with O-N in GaN. Our calculations thus predict that isolated oygen acts as a DX-type center in AlxGa1-xN alloys. Results for other oxygen point defect configurations and for the dominant native defects are also presented.