Thin films of ZnO were grown onto ScAlMgO4 substrates and were characterized by means of positron annihilation. The Doppler broadening spectra of annihilation radiation and photoluminescence spectra for ZnO films deposited by laser molecular-beam epitaxy, and for monocrystalline ZnO, were measured. Although the lifetime of the positrons in monocrystalline ZnO was close to the lifetime of positrons annihilated from the free state, the diffusion length of positrons was shorter than that for typical defect-free materials. This was attributed to scattering of the positrons by native defects. In the case of ZnO films, a correlation was observed between the defects and the lifetimes of bound exciton emissions. The main defect species which were detected by positron annihilation were Zn vacancies or other related defects. Isochronal annealing (750 to 850C) was found to introduce additional vacancy-type defects into the film. However, the lifetime of bound exciton emissions was hardly changed by the annealing.

Defects in ZnO Thin Films Grown on ScAlMgO4 Substrates Probed by a Monoenergetic Positron Beam. Uedono, A., Koida, T., Tsukazaki, A., Kawasaki, M., Chen, Z.Q., Chichibu, S., Koinuma, H.: Journal of Applied Physics, 2003, 93[5], 2481-5