Structural and optical properties of Fe-doped ZnO transparent thin films

We investigated the structural, morphological, and optical properties of Fe-doped ZnO transparent thin films spin coated on ordinary and FTO glass substrates using X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectrometric reflectometry (SR) techniques. The XRD spectra showed the polycrystalline films with a preferential orientation along the c-axis and without any impurity phases. SEM images revealed that the randomly oriented matrix shaped nanoparticles of ZnO doped with 1% Fe (with respect to Zn) transformed into cylindrical long grains at higher dopant concentration (4% Fe). The surface reflectance of the Fe-doped ZnO film, particularly in the wavelength range of 400-650 nm, was approximately two fold higher than the ones with un-doped ZnO film. However, the transmittance of the doped film decreased only by ~10%. The band gap, derived with the aid of measured transmittance curves, of un-doped ZnO thin film ca. 3.26 eV was decreased to ca. 3.21 eV when Fe ions were doped into the film and was independent to the dopant concentration.