Gallium and nitrogen vacancies in GaN: Impurity decoration effects

Abstract

We have performed a systematic study of magnesium and oxygen doping as well as the effect of annealing in metal organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE) grown Gallium nitride (GaN) by positron annihilation spectroscopy. The formation of vacancy-type defects identified here depends on the presence of impurity atoms as well as their concentrations. O doping generates vacancies in the Ga sublattice with concentrations proportional to the amount of O, whereas Mg atoms introduce vacancies in the N sublattice. In addition at very high Mg doping levels ( > 10 19 cm - 3 ) vacancy clusters with inhomogeneous depth profile are formed. Annealing dissociates vacancy-impurity pairs in MOCVD GaN:Mg and the defect profile is made homogeneous by vacancy migration. Vacancies in the Ga sublattice of HVPE GaN:O are shown to be complexed with O atoms by comparing the GaN:O data with the one obtained from electron-irradiated GaN, which contains isolated Ga vacancies. This comprehensive study shows that vacancy-type defects decorated by impurities are formed in both sublattices of GaN depending on the doping of the material.