Structural and optoelectronic properties of Zn-incorporated CdO films prepared by sol-gel method

Light zinc incorporated CdO thin films with various Zn concentrations have been prepared on glass and silicon substrates using sol-gel spin coating technique. The films were characterised by the X-rays fluorescence (XRF), X-ray diffraction (XRD), optical absorption spectroscopy, and dc-electrical measurements. The %Zn content in the samples was measured with XRF method and the crystalline structure was determined by XRD method. The experimental results indicated that the major mechanism for light doping of Zn2+ ions is controlled by their occupation of interstitial positions and/or structural vacancies. Furthermore, some of incorporated Zn ions accumulate on crystallite boundaries causing increase in the grain size by joining more crystallites together. The bandgap of Zn-incorporated CdO suffers narrowing by about 8% due to a light (0.51%) Zn-incorporation. The electrical behaviours of the Zn-incorporated CdO films show that they are degenerate semiconductors. It was observed that Zn2+ ions with 0.51% incorporation causes increase in electrical conductivity of host CdO film by about 200% and carrier concentration by about 270%, but decrease in the carrier mobility by about 20%. The phenomenological dependence of the bandgap on the carrier concentration was described according to the available models. Finally, the absorption in the NIR spectral region was studied in the framework of classical Drude theory. (C) 2012 Elsevier B.V. All rights reserved.