Oxygen adsorption and incorporation at irradiated GaN(0001) and GaN(000 1̄) surfaces: First-principles density-functional calculations

Density functional theory calculations of oxygen adsorption and incorporation at the polar GaN(0001) and GaN(000 1̄) surfaces have been carried out to explain the experimentally observed reduced oxygen concentration in GaN samples grown by molecular beam epitaxy in the presence of high energy (∼10 keV) electron beam irradiation. Using a model in which the effect of the irradiation is to excite electrons from the valence to the conduction band, we find that both the energy cost of incorporating oxygen impurities in deeper layers and the oxygen adatom diffusion barriers are significantly reduced in the presence of the excitation. The latter effect leads to a higher probability for two O adatoms to recombine and desorb, and thus to a reduced oxygen concentration in the irradiated samples, consistent with experimental observations.