Influence of thickness and crystalline structure on thermal and optical properties of ZnO thin films

Measurements of the temperature dependence of refractive index of ZnO thin films and thermal diffusivity using photothermal deflection technique are presented. Thin film thickness and surface homogeneity were found to be the effective parameters on optical and thermal properties of the thin films. High refractive index gradient with temperature was found for films of a nonuniform distribution and gathered in clusters, and a high predicted value for thermal diffusivity. Optical properties of the thin films revealed that films with disorder in the deposition and gathered clusters showed poor transmittance in visible region with a pronounced peak in the near IR, and also a reduction in the band gap. A detailed parametric analysis using analytical solution of one-dimensional heat equation had been performed. A discontinuity in the temperature elevation at the ZnO-glass interface was found.