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 Zn{sub 0.98}Cu{sub 0.02}O 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 Zn{sub 0.98}Cu{sub 0.02}O films were investigated by X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that Zn{sub 0.98}Cu{sub 0.02}O 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 Zn{sub 0.98}Cu{sub 0.02}O films and surface roughness increases. XRD and XPS data show that the valence state of copper in the Zn{sub 0.98}Cu{sub 0.02}O films is Cu{sup 2+}. The transparency of all films is more than 85% in the visible region.