Undoped ZnO single crystals were implanted with multiple-energy
N+
ions ranging from 50 to 380 keV with doses from
1012 to
1014 cm−2. Positron 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-implantation-induced 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.