Effect of Co doping on optical parameters of SnO2 thin films

SnO2 thin films are deposited using spray pyrolysis technique on p-type silicon (Si) substrate by varying the Cobalt (Co) doping ratio from 3 to 5 at % in order to investigate the effect of the doping on the optical parameters of these films. Optical reflectance measurements are performed both for films and substrate. A simple analysis which is created as a combination of three different methods proposed earlier including the effect of the substrate is applied for the optical characterization of Co-doped SnO2 thin films. In addition to thickness, optical parameters such as refraction index and extinction coefficients are also obtained accurately, by applying this created procedure. The optical band gap and Urbach energy of the films are determined from the spectral dependence of the absorption coefficient. The refraction index and band gap energy of SnO2 films are found to be decreasing whereas Urbach energy is found to be increasing with increasing Co doping ratio. The roughness value of Co-doped SnO2 thin films on p-type Si is obtained with such a high precise only from reflectance spectrum.