Positron annihilation spectroscopy was used to study the vacancy-type defects produced in films grown by metal-organic chemical vapor deposition onto various sapphire orientations. The Zn vacancies were the defects which controlled the positron annihilation spectra at room temperature. When close to the interface (<500nm), their concentration depended upon the surface plane of sapphire on

which the ZnO film was grown. The Zn vacancy content in the film decreased with thickness and, above 1μm, it was independent of the substrate orientation.

Zinc Vacancies in the Hetero-Epitaxy of ZnO on Sapphire - Influence of the Substrate Orientation and Layer Thickness. Zubiaga, A., Tuomisto, F., Plazaola, F., Saarinen, K., Garcia, J.A., Rommeluere, J.F., Zuñiga-Pérez, J., Muñoz-Sanjosé, V.: Applied Physics Letters, 2005, 86[4], 042103