N+ ion-implantation-induced defects in ZnO studied with a slow positron beam

Abstract

Undoped ZnO single crystals were implanted with multiple-energyN+ ions ranging from 50 to 380 keV with doses from1012 to1014 cm−2. Positron annihilation measurements show that vacancy defects are introduced inthe implanted layers. The concentration of the vacancy defects increases withincreasing ion dose. The annealing behaviour of the defects can be divided intofour stages, which correspond to the formation and recovery of large vacancyclusters and the formation and disappearance of vacancy–impurity complexes,respectively. All the implantation-induced defects are removed by annealing at1200 °C. Cathodoluminescence measurements show that the ion-implantation-induced defects actas nonradiative recombination centres to suppress the ultraviolet (UV) emission. Afterannealing, these defects disappear gradually and the UV emission reappears, whichcoincides with positron annihilation measurements. Hall measurements reveal that afterN+ implantation, the ZnO layer still shows n-type conductivity.