Effect of Co-doping level on physical properties of ZnO thin films

Abstract

Abstract In this work pure and Co doped ZnO thin films have been deposited onto glass substrate at different levels of Co-doping. XRD, SEM, EDX, XPS and optical spectroscopy (linear and nonlinear) techniques have been used to investigate all films. The grain size was found to increase upon Co doping from 26.2 nm to 50.3 nm. The elemental percentage obtained by EDX and XPS confirm the existence of Co in doped films which increases as increasing the percentage of cobalt salt in the starting solution. The optical band gap was estimated and found to decrease in the low Co concentrations and increases again in higher Co concentration. The dispersion was found to change from anomalous to normal upon Co-doping. In Co-doped ZnO films the dispersion changes to be normal again were modelled using the single oscillator model. The plasma frequency, the refractive index at high wavelength, the optical moments of the films were determined. The nonlinear optical properties of all films were studied using nanosecond 532 nm laser, the doped materials exhibit reverse saturable absorption and negative nonlinear refraction in contrary to pure ZnO which has positive nonlinear refraction.