Oxygen vacancies in ZnO

Abstract
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 V O is not a shallow donor, but has a deep ε ( 2 + ∕ 0 ) level at ∼ 1.0 eV 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. B71, 125210 (2005)].