Enhanced near-band edge emission in pulsed laser deposited ZnO/c-sapphire nanocrystalline thin films

We report on the enhanced near-band edge emission with negligible defect-assisted emission in ZnO nanocrystalline thin films of varying thickness on c-sapphire substrates. X-ray diffraction studies reveal wurtzite structure of thin films grown preferentially along (002) plane. The crystallinity and grain size of the deposited films have been increased with increase in film thickness. The band gap of the films was calculated by Tauc’s plot which shows negligible change in band gap with increase in thickness of ZnO film. The various Raman modes observed in ZnO thin films of different thicknesses support the formation of hexagonal wurtzite structure. The room temperature photoluminescence (PL) spectrum shows the strong near-band edge emission in the wavelength range 378–381 nm which further enhances with film thickness. The enhanced PL emission in near ultraviolet visible (UV) region with negligible defect-assisted emission may find potential applications in ZnO-based UV-excited light-emitting diodes.