Preparation And Characterization Of ZnO Thin Films With C-axis Preferred Orientation By Sol-Gel Method

Zinc oxide is a direct wide band gap II-VI compound semiconductor, which is considered to be a new photoelectric material in short wavelength taking place of GaN. Recently, transparent thin film transistors using ZnO channel layers have attracted considerable attention, while preparation of high-quality large scale ZnO thin films by low-cost method is the key to this application.Basic properties of ZnO are reviewed in this thesis, and then photoelectric applications of ZnO, especially ZnO thin film transistors, are described. The principles and research progress of ZnO films preparation by sol-gel method are given.ZnO films were prepared on glass substrates and silicon substrates by sol-gel dip-coating and spin-coating method respectively, using zinc acetate dihydrate, monoethanolamine and 2-methoxyethanol as precursors. The crystalline structure, optical properties and thickness of films were characterized by X-ray diffractometer, ultraviolet-visible spectrophotometer, fluorescence spectrophotometer and ellipsometer. The prepared ZnO films had good crystallinity and c-axis preferred orientation. A strong near-bandgap ultraviolet emission peak, a violet emission peak, and a weak deep energy level defects related emission peak appeared in photoluminescence spectrum. The transmittance of ZnO films deposited on glass substrates was 75% in the visible range, and an increase of 60nm in thickness was observed after each coating.The influences of sol concentration, aging time, preheating temperature and annealing temperature on c-axis preferred orientation and transmittance of ZnO films were studied by orthogonal experiments, and the results showed that the important factors were preheating temperature and annealing temperature. Based on the results of orthogonal experiments, the influences of processing parameters, including preheating temperature, annealing temperature, annealing time, coating number, aging time and annealing atmosphere, on the properties of ZnO films were studied in details respectively. Preheated at 500°C after each coating, and finally annealed at 525°C for films on glass substrates and 750°C for films on silicon substrates, the ZnO films have best c-axis preferred orientation. Longer aging time benefits the crystallinity and transmittance of films. Annealing in nitrogen gas reduces the resistance of ZnO films.