Photoluminescence spectra in the band-edge emission region of very high quality undoped ZnO were studied as a function of sample growth methods and conditions, and the measurement temperature. As a result, the defect types responsible for emission peaks observed in the band-edge emission region could be classified into 3 groups. In addition, the lattice defects which were probably responsible for the emission peaks were suggested to be O vacancies and/or interstitial Zn, or residual Al impurities.

Characterization of ZnO Crystals by Photoluminescence Spectroscopy. Shibata, H., Watanabe, M., Sakai, M., Oka, K., Fons, P., Iwata, K., Yamada, A., Matsubara, K., Sakurai, K., Tampo, H., Nakahara, K., Niki, S.: Physica Status Solidi C, 2004, 1[4], 872-5