Abstract
By employing picosecond time-resolved photoluminescence, we investigated the temporal behavior of the near band-gap exciton emission located at ∼3.264 eV of a ZnO epilayer deposited onto a (1 0 0) silicon substrate by plasma-assisted MOCVD. The emission exhibits a biexponential decay behavior composed of an initial fast component (30–50 ps) followed by a second slower component (100–400 ps). The extracted time constant for the capture of free-excitons at the band-tail states is in the order of 30 ps. The results strongly suggest that the decay of the exciton population is governed by the initial fast decay due to the capture of excitons and trapping of carriers by deep centers at defects and/or impurities, and the measured slower decay component is due to the radiative recombination of free- or localized-excitons.
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