Ultraviolet stimulated emission from bulk and polycrystalline ZnO thin films with varying grain sizes

We report on the stimulated emission behaviour of bulk and polycrystalline ZnO thin films grown on sapphire substrates with the pulsed laser deposition (PLD) technique. The PLD samples were annealed in an O2 atmosphere at various temperatures. It has been reported previously that these samples show a continuous increase in the polycrystalline grain size with increasing annealing temperature. Measurements of optically pumped stimulated emission from these samples have been made using an Nd:YAG laser operating at 355 nm. We give identifications of the various features in the spectra and discuss the effect of the various grain sizes on the stimulated emission process in the PLD samples.