Structural and optical properties of Cr-doped ZnO thin films

In the present work, chromium (Cr)-doped zinc oxide (ZnO) thin films were prepared on silicon and glass substrates by using the sol–gel spin-coating technique. The influence of chromium doping on the structural and optical properties of zinc oxide films was investigated. The X-ray diffraction results reveal that the films are polycrystalline in nature with hexagonal wurtzite structure. The absence of secondary diffraction peaks other than those for zinc oxide suggests that the chromium ions successfully replaced zinc (Zn) ions and were incorporated into the crystal-lattice positions. The average grain size and the strain arising due to the introduction of chromium ions in the lattice were obtained by using Williamson–Hall analysis. The surface morphology of the films was observed by field emission scanning electron microscopy. The Raman spectra of the films show a peak at 434 cm⁻¹ corresponding to E₂ (high) mode of crystalline zinc oxide wurtzite structure, and the intensity of this mode decreases with increase in chromium doping. The films are highly transparent (∼90%) in the visible region, which reduces with chromium doping.