Influence of dopants and substrate material on the formation of Ga vacancies in epitaxial GaN layers - art. no. 045205

We have applied a low-energy positron beam and secondary ion mass spectrome try to study defects in homoepitaxial and heteroepitaxial GaN layers. Posit ron experiments reveal high concentrations of Ga vacancies in nominally und oped n-type GaN, where the conductivity is due to unintentional oxygen inco rporation. Ga vacancies are observed in both homoepitaxial and heteroepitax ial layers, indicating that their formation is independent of the dislocati on density. No Ga vacancies are detected in p-type or semi-insulating sampl es doped with Mg, as predicted by the theoretical formation energies. In sa mples where n-type conductivity is due to Si doping and the incorporation o f oxygen impurities is suppressed, the concentration of Ga vacancies is muc h lower than in n-type samples containing oxygen. This indicates that the p resence of oxygen donor in GaN promotes the formation of Ga vacancy. We sug gest that this effect is due to the creation of V-Ga-O-N complexes during t he epitaxial growth.