Ion-Implantation Induced Defects in ZnO Studied by a Slow Positron Beam

Abstract

Undoped ZnO single crystals were implanted with multiple-energy N + ions ranging from 50 to 380 keV with doses from 10 12 to 10 14 cm −2 .P os itron annihilation measurements show that vacancy defects are introduced in the implanted layers. The concentration of the vacancy defects increases with increasing ion dose. The annealing behaviour of the defects can be divided into four stages, which correspond to the formation and recovery of large vacancy clusters and the formation and disappearance of vacancy–impurity complexes, respectively. All the implantation-induced defects are removed by annealing at 1200 ◦ C. Cathodoluminescence measurements show that the ion-implantationinduced defects act as nonradiative recombination centres to suppress the ultraviolet (UV) emission. After annealing, these defects disappear gradually and the UV emission reappears, which coincides with positron annihilation measurements. Hall measurements reveal that after N + implantation, the ZnO layer still shows n-type conductivity.