Effect of annealing on Zn1−xCoxO thin films prepared by electrodeposition

Polycrystalline thin films of Zn_1−xCo_xO with different cobalt (Co) content were grown on indium tin oxide (ITO) substrates by cathodic electrodeposition technique and subsequently annealed in air at 400 °C. The effect of annealing in their structural, optical and chemical properties has been characterized by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman scattering and optical spectroscopy. Our measurements indicate that moderate annealing increases the crystal quality of the films. The films are highly transparent in the visible range and evidence an increase of the band gap and of the intensity of three typical Co absorption bands in the visible with the amount of Co. Thermal annealing produces an increase of the intensity of the Co²⁺-related absorption bands revealing that higher amount of Co atoms are occupying Zn sites.