By combining results from positron annihilation and photoluminescence spectroscopy with data from Hall effect measurements, the characteristic deep level emission centered at ∼1.75eV and exhibiting an activation energy of thermal quenching of 11.5meV was associated with the zinc vacancy. Further, a strong indication that oxygen interstitials act as a dominating acceptor was derived from the analysis of charge carrier losses induced by electron irradiation with variable energy below and above the threshold for Zn-atom displacement. It was also demonstrated that the commonly observed green emission was related to an extrinsic acceptor-like impurity, which may be readily passivated by oxygen vacancies.

Zinc Vacancy and Oxygen Interstitial in ZnO Revealed by Sequential Annealing and Electron Irradiation. Knutsen, K.E., Galeckas, A., Zubiaga, A., Tuomisto, F., Farlow, G.C., Svensson, B.G., Kuznetsov, A.Y.: Physical Review B, 2012, 86[12], 121203