Annealing process of ion-implantation-induced defects in ZnO: Chemical effect of the ion species

ZnO single crystals implanted with O+ and B+ ions were studied by positron annihilation and Raman scattering measurements. Positron annihilation results show that vacancy clusters are generated by implantation. For the B+-implanted sample, the vacancy clusters have a sufficient increase in size and evolve into microvoids after annealing up to 500°C. These microvoids need a high temperature of 900–1000°C to be annealed out. However, for the O+-implanted sample, the size of the vacancy clusters shows only a slight increase during annealing process, and they are removed at much lower temperature of 700–800°C. The different annealing process is supposed to be due to the chemical effect of boron impurities. Raman measurements reveal the production of oxygen vacancies by implantation. In the B+-implanted sample they have high thermal stability up to 700°C, while in the O+-implanted sample they are annealed out early at 400°C. It is thus suggested that the boron impurities might form complexes with oxygen interstitials and stabilize oxygen vacancies, which favors the vacancy agglomeration process.