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

Abstract

Influences of point defects on the nonradiative processes in ZnO were studied using steady-state and time-resolvedphotoluminescence(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 (τ nr ). Density or size of Znvacancies (V Zn ) decreased and τ nr increased with increasing growth temperature in heteroepitaxialfilmsgrown on a ScAlMgO 4 substrate. Use of homoepitaxial substrate further decreased the V Zn density. However, τ nr was the shortest for the homoepitaxialfilm; i.e., no clear dependence was found between τ 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.