Determination and Analysis of Structural and Optical Properties for Thermally Evaporated ZnO Thin Films

Abstract

ZnO films have been deposited on glass slide substrates at room temperature by thermal evaporation technique. The prepared samples were annealed at temperature of 300°C and 400°C in air atmosphere. Optical and structural properties of as-deposited films have been compared by that of the annealed samples. X-ray diffraction (XRD) patterns of the obtained films showed that they have polycrystalline and exhibit wurtzite structure. Micro-structural properties such as mean crystallite size and micro-strain were discussed from XRD peak broadening. Optical properties were identified by measuring transmittance using UV-Vis spectrophotometer. The optical constants such as the refractive index n, extinction coefficient k as well as films’ thickness were calculated in the spectral range of 350-800 nm from transmittance data using a reverse engineering method (point-wise unconstrained minimization approach, PUMA). Dispersion of refractive index shows similar trend as Cauchy relation. Absorption coefficient depicts a maximal value around 3.33 eV for annealed samples. Using balance between electrical power and emissive power, the temperature of tungsten furnace was calculated under deposition condition. The connection between temperature and vapor pressure of ZnO was estimated by the Clausius-Clapyeron equation and thermochemical data.