First-principles calculations were performed which showed that the oxygen vacancy was not a shallow donor, but had a deep level at about 1.0eV below the conduction band. The negative-U behavior that caused the 1+ charge state to be unstable was associated with large local lattice relaxations. A detailed configuration coordinate diagram was presented which provided a detailed interpretation to be made of recently reported optically detected electron paramagnetic resonance measurements.

Oxygen Vacancies in ZnO. Janotti, A., Van De Walle, C.G.: Applied Physics Letters, 2005, 87[12], 122102