Studies of Defects in ZnO by Positron Annihilation

In order to investigate the basic properties of radiation-induced defects in ZnO crystals, positron annihilation lifetime and Doppler-broadening measurements were performed on crystals sinterd for 18 hours at 1200 °C and irradiated with 3 MeV protons at 223 K. The irradiation induced a colour change of the specimens from the original yellowish-white to dark orange or even brown. Isochronal annealing experiments showed three annealing stages, centred at about 150 °C, 500 – 550 °C, and 750 °C, respectively. These stages are related to the annealing of variously sized vacancy complexes.