Energy Variable Slow Positron Beam Study of Li⁺-Implantation-Induced Defects in ZnO

ZnO films grown on sapphire substrates are implanted with 100-keV Li ions up to a total dose of 1×10^-16 cm^-2. Vacancy-type defects, mostly vacancy clusters, are observed by positron annihilation measurements after implantation. Upon annealing, they first have an agglomeration process which leads to the growth in the vacancy size. After annealing at about 500°C, vacancy clusters grow into microvoids, which is indicated by the positronium formation. With annealing temperature increases to above 500°C, the microvoids begin to recover, and finally all the implantation-induced vacancy defects are removed at 1000°C. No Li nanoclusters can be observed after Li⁺ implantation.