Structural properties and optical constants of Co-doped ZnO thin films deposited using sol-gel spin-coating

Sol-gel spin-coating was used to deposit Co-doped ZnO thin films onto quartz glass substrates. A secondary phase could not be detected in the films from their X-ray diffraction patterns, implying that substituting Co²⁺ ions into the ZnO matrix did not modify its wurtzite structure. We used an ultraviolet (UV)-visible spectrometer to measure the optical properties of the Co-doped ZnO thin films at room temperature to demonstrate that Co²⁺ ions had been substituted for Zn²⁺ ions in the wurtzite structure. The UV transmittance spectra for the films showed absorption peaks at 568.1, 609.3, and 660.1 nm. Moreover, the area under the absorption wells between 500 and 700 nm increased with increasing Co concentrations in the films. These results indicate that Co²⁺ ions had been substituted for Zn²⁺ ions in the crystal lattice of the films.