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.

Defects in as-grown and ion-bombarded p-InP crystals have been investigated by positron lifetime measurements. The result showed that indium vacancies existed in as-grown p-InP. In addition, Zn impurities Zn − In were also observed, which are negative and act as shallow trapping centres at low temperatures. Ion bombardment at lower dose introduced some monovacancies, and with increasing ion dose, divacancies were also observed, which coexisted with monovacancies. The temperature experiment showed that antisite defects were also produced upon bombardment, which we attribute to the negatively charged In P antisites.