Low-temperature growth of ZnO epitaxial films by metal organic chemical vapor deposition

ZnO films were grown on Al2O3 (0001) substrates by metal organic chemical vapor deposition at temperatures of Tg=150∼300 °C. Epitaxial growth was obtained for Tg≥200 °C. The in-plane orientation of the ZnO unit cells was found to change from a no-twist one with respect to that of the substrate at Tg=200 °C to a 30°-twist one at Tg=300 °C. Absorption and photoluminescence were observed from the film grown at 150 °C, although there was no evidence of epitaxial growth. Films grown at Tg≤200 °C exhibited smoother surfaces. Moreover, all the films grown at Tg=150∼300 °C revealed acceptor-related emission peaks, indicating the incorporation of acceptors into the films.