Oxygen vacancies in ZnO

The electronic properties of ZnO have traditionally been explained by invoking intrinsic defects. In particular, the frequently observed unintentional n-type conductivity has often been attributed to oxygen vacancies. We report first-principles calculations showing that the oxygen vacancy VO is not a shallow donor, but has a deep ε(2+∕0) level at ∼1.0eV below the conduction band. The negative-U behavior that causes the 1+charge state to be unstable is associated with large local lattice relaxations. We present a detailed configuration coordinate diagram, which allows us to provide a detailed interpretation of recently reported ODEPR (optically detected electron paramagnetic resonance) measurements L. S. Vlasenko and G. D. Watkins, Phys. Rev. B 71, 125210 (2005).