Vacancies in wurtzite GaN and AlN

Vacancies in wurtzite GaN and AlN are studied using a computational method which is based on the density functional theory (DFT) and takes into account the errors arising from use of finite-sized supercells and the DFT band gap underestimation. Negatively charged N vacancies in GaN and AlN are found to be stable, with formation energies similar to and higher than those of Ga and Al vacancies in n-type material under Ga- and Al-rich growth conditions, respectively. The localization and energies of the defect levels close to the computational conduction band edge are considered in detail.