Oxygen and zinc vacancies were unambiguously shown to be formed in as-grown

ZnO bulk crystals grown from the melt without being subjected to irradiation, from

electron paramagnetic resonance and optically detected magnetic resonance

studies. Concentrations of the defects in their paramagnetic charge states VO

+ and

VZn

- were estimated to be about 2 x 1014 and 1015/cm3, respectively. The VZn

- defect

was concluded to act as a deep acceptor and to exhibit large Jahn–Teller distortion

by 0.8eV. The energy level of the defect corresponding to the (2–/–) transition was

Ev + 1.0eV. The isolated Zn vacancy was found to be an important recombination

centre and was concluded to be responsible for the red luminescence centred at

around 1.6eV. On the other hand, the oxygen vacancy seems to be less important in

carrier recombination as it could be detected only in EPR but not in optically

detected magnetic resonance measurements. Neither isolated VZn

- nor VO

+ centres

participate in the so-called 'green' emission. It was also shown that whereas the concentrations of both defects can be reduced by post-growth annealing, the Zn

vacancy exhibits higher thermal stability. The important role of residual

contaminants such as Li in the annealing process was underlined.

Oxygen and Zinc Vacancies in As-Grown ZnO Single Crystals. X.J.Wang,

L.S.Vlasenko, S.J.Pearton, W.M.Chen, I.A.Buyanova: Journal of Physics D, 2009,

42[17], 175411