Influence of Fe-doping on the optical and electrical properties of ZnO films

• The preferential orientation of the crystallites depends on the Fe concentration.
• Both Fe3+ as well as the Fe2+ ions substitutes Zn2+ in prepared films.
• The red-shift of the Eg edge is attributed to the sp–d spin-exchange interactions.
• Fe doping decreases the conductivity of ZnO with two orders of magnitude.

We have prepared Fe doped ZnO films, by spin coating, and investigated their structure, morphology, optical and electrical properties by means of the X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, UV–vis–NIR spectrometer and the temperature dependence of electrical conductivity measurements, respectively. XRD results indicates that the films under study posses a polycrystalline structure. A deterioration of the crystallite preferentially orientation, with the increase of Fe doping concentration, was observed. The optical transmittance measurements reveal that the transparency of studied films decreases with the increase of Fe concentration in ZnO. The electrical behavior was analyzed during a heat treatment. The experimental results indicate that the introduction of Fe impurities decreases the conductivity of ZnO with two orders of magnitude. Mott variable range hopping model was proposed to analyze the mechanisms of electronic transport, in low temperature ranges.