Study On Photoluminescence Properties Of Undoped ZnO Films

Polycrystalline zinc oxide (ZnO) films are one of very useful materials, and are widely used in piezoelectric device, transparent conducting electrodes, photo-electric device and gas sensors because of their excellent characteristics. In this dissertation, we report the systematical work on preparation, and optical properties of polycrystalline ZnO films.ZnO films were deposited on n-type silicon (Si) substrate by reactive radio frequency sputtering (RF) technique with a ZnO target in the mixed gas of Ar and O2 The effects of deposition condition, included RF power, sputtering pressure the distance of substrate to target on growth rate of ZnO films have be studied in detail.The microstructure of films were characterized by XRD SEM spectra. The XRD measurements show all the films have (002) preferred orientation. The SEM measurements show the morphology of ZnO grains is uniformity and dense.We report the effects of the growth ambient, the annealing temperature and annealing ambient on the photoluminescence (PL) emission properties of ZnO films deposited on Si substrates by rf magnetron sputtering. The results show that the crystal quality of ZnO films has been improved markedly by annealing, and the intensity of UV peak increases evidently by annealing. The UV emission is attributed to free exciton transition. The intensity of UV peak is related to the crystal quality of ZnO films. The blue emission and the green emission are related to Zinc and Oxygen vacancies in ZnO films. The concentrations of Zinc and Oxygen vacancies are changed through annealing in Oxygen-deficient or Oxygen-rich ambient and changing the gas flux ratio of O2 to Ar during the sputtering. Then the emission peak position and emission intensity of ZnO films are changed. The blue emission may correspond to the electron transition from the bottom of the conduction band to the acceptor level composed of zinc defects, the green emissionmay correspond to the electron transition from the donor level caused by oxygen vacancies to the acceptor level caused by zinc vacancies. The annealing temperature is an important parameter. Desorption and adsorption of oxygen are controlled by annealing temperature, then the densities of oxygen and Zinc vacancies are controlled by it.