An investigation was made of the intrinsic defects, in films grown by molecular beam epitaxy, by annealing them in O2 and N2 atmospheres. It was found that there was a good correlation between the annealing conditions and the photoluminescence characteristics. The results of annealing experiments suggested that a photoluminescence at 3.358eV was caused by excitons bound to O vacancies. A green-yellow emission at around 2.3eV was also observed in as-grown epitaxial films. This emission became weak, and the electron concentration increased, when films were annealed in an O2 atmosphere at 1000C or in a N2 atmosphere at 700C. Since the donor in undoped ZnO was related to the O vacancy, the observed green-yellow emission at around 2.3eV was suggested to be caused by defects other than O vacancies. The experimental results implied that it was related to interstitial Zn.

Intrinsic Defects in ZnO Films Grown by Molecular Beam Epitaxy. T.Tatsumi, M.Fujita, N.Kawamoto, M.Sasajima, Y.Horikoshi: Japanese Journal of Applied Physics, 2004, 43[5A], 2602-6