Localization of oxygen donor states in gallium nitride from first-principles calculations

Using first-principles band structure methods, the electronic structure and local geometry of oxygen impurities in GaN have been investigated as a function of oxygen concentration. The concentrational variation has been simulated using various supercells. In order to test the validity of ``rigid band'' models usually employed to describe the effect of impurities on the electronic structure and associated properties of wide band gap semiconductors, the spatial localization of donor states associated with oxygen atoms at the nitrogen site has been carefully explored. For all the supercells studied in this work, the energy bands near the bottom of the conduction band are found to be severely perturbed. The donor electrons are found to occupy extended states. However, with increasing dilution of impurities, the donor electron tends to localize near the impurity ion. This localization monotonically progresses with decreasing oxygen concentration.