Effect of Er concentration on surface and optical properties of K doped ZnO sol-gel thin films

The K doped and (K, Er) codoped ZnO thin films were prepared on glass substrate by sol gel method. The microstructures and optical properties of the doped and codoped films are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectra (EDX), atomic force microscope (AFM) and UV-Vis spectroscopy. All the doped and codoped films have polycrystalline nature with wurtzite structure and strong c-axis orientation. A decreases in particle size is observed with the increase of Er concentration in K doped ZnO films. The SEM and AFM images show wrinkle structure formation on the film surfaces and its width increases with respect to Er concentration. Observed average surface roughness of the K doped films is 9.79 nm and (K, Er) codoped film is 14.80 nm. The surface morphology properties of the films are analyzed by fractal dimension parameter. Doped and codoped elemental composition is confirmed from the EDX spectra. The observed average transmittance of doped and codoped films is around 85% and a blue shift of the band is observed after the Er doping in K doped ZnO films. The Urbach tail parameter and optical constants such as refractive index, extinction coefficient, and dielectric constants have been calculated for these films. The dispersion parameters such as single-oscillator energy and dispersive energy are discussed in terms of the single-oscillator Wemple-DiDomenico model. (C) 2015 Elsevier Ltd. All rights reserved.