Influence of Al dopant on microstructure and optical properties of ZnO thin films prepared by sol–gel spin coating method

Zinc oxide thin films are prepared on c-plane sapphire substrates using the sol–gel spin coating method. After coating the samples were annealed at 873 K. Effects of Al doping on the morphological, microstructural and optical properties were examined. Both the pure and Al doped ZnO samples are (0 0 0 2) oriented. Undoped ZnO samples posses film-like morphology where as Al doping resulted in the formation of disconnected spherical grains. Cathodoluminescence spectroscopy measured at room temperature shows a strong ultra violet exciton emission around 382 nm along with deep level green emission due to defects around 500 nm for undoped ZnO film. Excitonic emission blue shifted to 380 nm and increase in deep level emission were observed for Al doped ZnO samples possibly due to size effects.