Hall effect, photoluminescence spectroscopy (PL), mass spectroscopy and X-ray diffraction have been used to study bulk
ZnO single crystal grown by a closed seeded chemical vapor transport method. Enhancement of n-type electrical
conduction and increase of nitrogen concentration are observed of the ZnO samples after high temperature annealing.
The results suggest that vacancy is dominant native defect in the ZnO material. These phenomena are explained by a
generation of shallow donor defect and suppression of deep level defects in ZnO after the annealing.