Structural Characteristics and Optical Properties of Thermally Oxidized Zinc Films

Zinc oxide (ZnO) thin films (with thickness ranged from 780 nm to 1150 nm) were prepared by thermal oxidation in air (at 600-700 K, for 20-30 min) of vacuum evaporated metallic zinc films. The Zn films were deposited on glass substrates at room temperature. The crystalline structure of ZnO thin film samples was investigated using X-ray diffraction technique. The diffraction patterns revealed that the ZnO thin films were polycrystalline and have a wurtzite (hexagonal) structure. The film crystallites are preferentially oriented with (002) planes parallel to substrate surface. Some important structural parameters (lattice parameters of the hexagonal cell, crystallite size, Zn-O bond length, residual stress, etc.) of the films were determined. The surface morphology of the prepared ZnO thin films, investigated by atomic force microscopy, revealed a uniform columnar structure. The spectral dependence of transmission coefficient has been studied in the wavelength range from 300 nm to 1700 nm. The optical energy band gap calculated from the absorption spectra (supposing allowed direct band-to-band transitions) are in the range 3.17-3.19 eV. The dependence of the microstructural and optical characteristics on the preparation conditions (oxidation temperature, oxidation time, etc.) of the oxidized zinc films is discussed.