Correlation between the photoluminescence lifetime and defect density in bulk and epitaxial ZnO

Influences of point defects on the nonradiative processes in ZnO were studied using steady-state and time-resolved photoluminescence (PL) spectroscopy making a connection with the results of positron annihilation measurement. Free excitonic PL intensity naturally increased with the increase in the nonradiative PL lifetime (tau(nr)). Density or size of Zn vacancies (V-Zn) decreased and tau(nr) increased with increasing growth temperature in heteroepitaxial films grown on a ScAlMgO4 substrate. Use of homoepitaxial substrate further decreased the V-Zn density. However, tau(nr) was the shortest for the homoepitaxial film; i.e., no clear dependence was found between tau(nr) and density / size of V-Zn or positron scattering centers. The results indicated that nonradiative recombination processes are not solely governed by single point defects, but by certain defect species introduced by the presence of V-Zn such as vacancy complexes. (C) 2003 American Institute of Physics.