Stabilization Mechanism of Vacancies in Group-III Nitrides: Exchange Splitting and Electron Transfer

We report first-principles calculations on mono-, di-, and tri-vacancies in group-III nitrides with clarifying two distinctive mechanisms in stabilization of the vacancy: Spin polarization due to exchange splitting of nitrogen-dangling bond states and electron transfer caused by breathing relaxation of cations. We also find that the significance of the two mechanisms strongly depends on the charge state of the vacancy and thus the Fermi-level position in the gap at which the charge state changes ( the thermodynamic charge-state level) cannot be determined from single-electron levels at a certain charge state.