The roles played by point defects and defect complexes in governing non-radiative processes in epilayers were studied by using time-resolved photoluminescence and slow positron annihilation measurements. The density or size of Zn vacancies (VZn) decreased, and the non-radiative photoluminescence lifetime increased, with increasing growth temperature for epilayers grown onto a ScAlMgO4 substrate. The steady-state free excitonic photoluminescence intensity increased with increasing photoluminescence lifetime at room temperature. The use of a homo-epitaxial substrate further decreased the VZn concentration. However, no perfect relationship between photoluminescence lifetime and density or size of VZn or other positron scattering centers was found. The results indicated that non-radiative recombination processes were governed not only by single point defects, but also by certain defect species that were introduced by the presence of VZn; such as vacancy complexes.

Direct Comparison of Photoluminescence Lifetime and Defect Densities in ZnO Epilayers Studied by Time-Resolved Photoluminescence and Slow Positron Annihilation Techniques. Koida, T., Uedono, A., Tsukazaki, A., Sota, T., Kawasaki, M., Chichibu, S.F.: Physica Status Solidi A, 2004, 201[12], 2841-5