Direct comparison of photoluminescence lifetime and defect densities in ZnO epilayers studied by time-resolved photoluminescence and slow positron annihilation techniques

摘要

The roles of point defects and defect complexes governing nonradiative processes in ZnO epilayers were studied using time-resolved photoluminescence (PL) and slow positron annihilation measurements. The density or size of Zn vacancies (V_(Zn)) decreased and the nonradiative PL lifetime (τ_(nr)) increased with higher growth temperature for epilayers grown on a ScAlMgO_4 substrate. Accordingly, the steady-state free exci-tonic PL intensity increased with increase in τ_(nr) at room temperature. The use of a homoepitaxial substrate further decreased the V_(Zn) concentration. However, no perfect relation between τ_(nr) and the density or size of V_(Zn) or other positron scattering centers was found. The results indicated that nonradiative recombination processes are governed not solely by single point defects, but by certain defect species introduced by the presence of V_(Zn) such as vacancy complexes.