Effects of Precursor Concentrations on ZnO Nano-fibrous Thin Films Grown by Using the Sol-gel Dip-coating Method

ZnO thin films were fabricated by using the dip-coating method to deposit solutions with different precursor concentrations on quartz substrates. The structural and the optical properties of the ZnO thin films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible spectroscopy. The average grain size in the ZnO thin films increased from 19.09 to 39.19 nm with increasing precursor concentrations, and nano-fibrous structures were observed on the surface when precursor concentrations above 0.4 M were used. The PL spectra, in all cases, showed near-band-edge (NBE) emission and deep-level emission (DLE). When the precursor concentrations were increased, the optical band gap values for the ZnO thin films shifted towards the blue region, and the values of the Urbach energy (E-U) gradually decreased from 154 to 65 meV.