Sol-gel synthesis and nanostructured semiconductor analysis of undoped and Cd-doped ZnO thin films

The semiconductor thin films of undoped and cadmium (Cd) doped zinc oxide (ZnO) via different concentrations (Cd: 2, 5 and 10 wt.%) were prepared by sol-gel route technique using a dip-coating method onto glass and silicon substrates. The Zinc acetate dehydrate (ZnAc), the Cadmium acetate dehydrate (CdAc), the 2-Methoxyethanol and the Ethanolamine were used as a starting material, doping, solvent and stabilizer, respectively. All films were annealed for 120 min at 500 °C. The samples were characterized by different analysis techniques to understand their structural, morphological and optical properties and its components such as the thin films surface are a nanometric crystallite size with a ganglia-like structure as observed by Environmental Scanning Electron Microscopy. The films were characterized by X-ray diffraction, it was crystallized in a hexagonal crystal structure with a highly c-axis preferred (002) orientation, and the crystallites size decrease from 30 to 23 nm with the increasing of cadmium doping. The Rutherford Backscattering Spectrometry and the Auger Electron Spectroscopy spectra given an idea in the thickness of the film by simulation and relation to the etching time respectively, where did the two agree that the film of ZnO doped 10 wt.% Cd is the thickest. All films exhibit an optical transmittance above 75 to 85% nm and a sharp absorption onset about 375 nm corresponding to the fundamental absorption edge 3.08 to 3.21 eV. The room-temperature luminescence emission spectra of these films were excited under the same conditions with 250 nm Xenon lamp excitation, showed an ultraviolet and visible emissions.