Depth-resolved cathodoluminescence, positron annihilation and surface photovoltage spectroscopy were used to determine the energy levels of Zn vacancies and vacancy clusters in bulk ZnO crystals. Doppler broadening-measured transformation of Zn vacancies to vacancy clusters with annealing shifts defect energies significantly lower in the ZnO band gap. Zn and corresponding O vacancy-related depth distributions provided a consistent explanation of depth-dependent resistivity and carrier-concentration changes induced by ion implantation.

Vacancy Defect and Defect Cluster Energetics in Ion-Implanted ZnO. Dong, Y., Tuomisto, F., Svensson, B.G., Kuznetsov, A.Y., Brillson, L.J.: Physical Review B, 2010, 81[8], 081201