Structural, linear and nonlinear optical properties of co-doped ZnO thin films

Different compositions of Co-doped zinc oxide [(Zn(1−x)Co x O) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10)] thin films were evaporated onto highly clean glass substrates by thermal evaporation technique using a modified source. The structural properties investigated by X-ray diffraction revealed hexagonal wurtzite ZnO-type structure. The crystallite size of the films was found to decrease with increasing Co content. The optical characterization of the films has been carried out using spectral transmittance and reflectance obtained in the wavelength range from 300 to 2500 nm. The refractive index has been found to increase with increasing Co content. It was further found that optical energy gap decreases from 3.28 to 3.03 eV with increasing Co content from x = 0 to x = 0.10, respectively. The dispersion of refractive index has been analyzed in terms of Wemple–DiDomenico (WDD) single-oscillator model. The oscillator parameters, the single-oscillator energy (E o), the dispersion energy (E d), and the static refractive index (n 0), were determined. The nonlinear refractive index of the Zn(1−x)Co x O thin films was calculated and revealed well correlation with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system.