Properties of Cu-doped ZnO films by RF sputtering method: Thickness dependence

We present results concerning the thickness dependence of structural, morphological and optical properties of the Zn0.98Cu0.02O films deposited on glass substrates using radio frequency (RF) sputtering method. The microstructure and the chemical state of oxygen, copper and zinc in ZnO and Zn0.98Cu0.02O films were investigated by X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that Zn0.98Cu0.02O films are the wurtzite structure with strong c-axis orientation. Crystallinity of the films is closely related to the film thickness. With increasing film thickness, there are more surface (mainly nanopores) defects existing in the Zn0.98Cu0.02O films and surface roughness increases. XRD and XPS data show that the valence state of copper in the Zn0.98Cu0.02O films is Cu2+. The transparency of all films is more than 85% in the visible region.