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 degrees C. These microvoids need a high temperature of 900-1000 degrees 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 degrees 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 degrees C, while in the O+-implanted sample they are annealed out early at 400 degrees 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. (C) 2006 American Institute of Physics.