The plane-wave pseudopotential method was used to study point defects in these materials. The calculations demonstrated a qualitatively different behavior of O impurities in the various substances. It was found that OAs in GaAs acted as a deep center with an off-center displacement and negative-U behavior; in agreement with experimental data. On the other hand, ON in GaN was a shallow donor with a low formation energy, and was suggested to act as a partial source of the unintentional n-type conductivity that was commonly observed in GaN. The O in AlN was also found to substitute easily for N. This was consistent with the experimentally observed large O concentrations in AlN. However, ON in AlN was shown to be a deep center, due to the wide band-gap; in contrast with ON in GaN. The calculations predicted that isolated O would act as a DX-type center in AlGaN.

T.Mattila, R.M.Nieminen: Physical Review B, 1996, 54[23], 16676-82