Pair vacancy defects in β-Ga2O3 crystal: Ab initio study

Despit many studies dedicated to the defects in β-Ga2O3, information about formation processes of complex "donor-acceptor" defects in β-Ga2O3 and their energetic characteristics is still very scarce. Meanwhile, complex defects, such as pair vacancies, are often indicated as electrically active centers that can play the role of acceptor defects. We have carried out comparative ab initio study of formation energies, as well as optical and thermodynamic transition levels of single and pair vacancies in β-Ga2O. It was confirmed that single gallium and oxygen vacancies are deep acceptors and deep donors, respectively. In this case, the optical transition levels of single gallium and oxygen vacancies are located in such a way that electrons can easily pass from donors to acceptors. Unlike single vacancies, a pair vacancy has a neutral state due to the location of the acceptor levels above the donor ones. However, if pair vacancies were thermally excited, the transition levels are shifted to ∼2.0 eV above the top of the valence band, at which the recombination of electrons and holes become possible, as is observed in the case of single vacancies.