Ab initio study of native point defects in ZnO under pressure

We investigate the formation enthalpies and transition energy levels for several native point defects in B1 phase of ZnO under applied hydrostatic pressure using density functional theory. The formation volume decreases gradually with increasing pressure, and increases linearly with the number of electrons adding to the system. In negatively charged state, the calculated formation enthalpy decreases with pressure, suggesting an increase in the equilibrium defect concentration. The behavior of the positively charged state is on the contrary, consistent with the results of the formation volume. In particular, the formation enthalpy of oxygen vacancy increases with pressure, which makes the defect formation harder under pressure. Under Zn-rich conditions, the “negative-U” phenomenon of oxygen vacancy, which appears under ambient conditions, vanishes with further increase in pressure when the Fermi enthalpy is close to the conduction band minimum.