Stimulated emission and time-resolved photoluminescence in rf-sputtered ZnO thin films

Stimulated emission (SE) was measured from ZnO thin films grown on c-plane sapphire by rf sputtering. Free exciton transitions were clearly observed at 10 K in the photoluminescence (PL), transmission, and reflection spectra of the sample annealed at 950degreesC. SE resulting from both exciton-exciton scattering and electron hole plasma formation was observed in the annealed samples at moderate excitation energy densities. The SE threshold energy density decreased with increasing annealing temperature up to similar to950 degreesC. The observation of low threshold exciton-exciton scattering-induced SE showed that excitonic laser action could be obtained in rf-sputtered ZnO thin films. At excitation densities below the SE threshold, time-resolved PL revealed very fast recombination times of similar to74 ps at room temperature, and no significant change at 85 K. The decay time for the SE-induced PL was below the system resolution of <45 ps. (C) 2004 American Institute of Physics.