Influence of Heat Treatment on the Optical Properties of Thermal Evaporated SnO2 Thin Films

In this investigation, the optical properties of the thermally evaporated SnO2 films and their dependence on the heat treatment were studied. The transmittance, T (lambda), spectra were measured over the spectral range of 0.2 to 0.8 mu m for SnO2 films that were annealed at different temperatures (300, 350, 400, 450, 500, 550 and 600 K) in vacuum for 1h. All films showed high transparency in the visible range and increased with increasing the wavelength. These films have become more transparent after annealing at different temperatures. The optical constants of annealed SnO2 films were obtained by modeling the measured transmission spectra. The best fit modeling of transmission spectra was obtained by applying Drude and OJL models combined with the effective medium approximation Bruggeman model. Increasing the annealing temperatures decreased both the refractive index and the extinction coefficient of the films. While the optical band gap energy increased from 3.05 to 4.11 eV by increasing the annealing temperature from 300 to 600 K, respectively. Analyzing the refractive index dispersion by using the Wemple-DiDomenico model revealed that the oscillator resonance energy E-o decreased whereas the oscillator dispersion energy E-d increased with increasing the annealing temperature.