Thickness-dependent optical properties of ZnO thin films

Spectroscopic ellipsometry was employed to study the thickness dependence of the optical properties of ZnO thin films. ZnO thin films with a nominal thickness of 100, 200, and 400 nm were deposited by filtered cathodic vacuum arc (FCVA) method. The optical band gap showed a slight blue shift with respect to the bulk value with increasingly thicker ZnO films deposited on Si, while no shift with thickness could be observed for ZnO films deposited on a SiO2/Si substrate, indicating a possible effect of the SiO2buffer layer on the film optical properties. The Urbach tail parameter E0increased as the film thickness is increased, indicating a decrease in the structural disorder with increasing film thickness.