Modulation of Physical Properties of Sprayed ZnO Thin Films by Substrate Temperature for Optical Applications
Abstract
We investigated the structural, electrical and optical properties of zinc oxide thin films as the n-type semiconductor. In the present paper, the effect of substrate temperature on the synthesis of ZnO thin films was carried out from 250∘C to 500∘C. ZnO thin films were deposited on glass substrates via ultrasonic spray technique with 0.2mol/L of zinc acetate dehydrate. The crystal quality of the thin films was analyzed by X-ray diffraction which results in modified substrate temperature. The optical transmittance and electrical conductivity measurements were carried out by Ultraviolet-visible spectrophotometer and four-point methods, respectively. Polycrystalline films with a hexagonal wurtzite structure with (100) and (002) preferential orientation corresponding to ZnO films were observed at high temperature. The optimal values of the average crystallite size of the ZnO films under consideration are observed beginning with 350∘C of substrate temperature. All films exhibit an average optical transparency of about 85% in the visible region. The shift of optical transmittance toward higher wavelength can be shown by the increase of bandgap energy from 3.245eV to 3.281eV with increasing substrate temperature of 250–500∘C. The observed Urbach energy of ZnO thin films decreases from 0.11311eV to 0.04974eV. At a high temperature, the electrical conductivity of ZnO films was increased from 3.87×10−3 to 41.58 (Ω.cm)−1 with the increasing substrate temperature from 350∘C to 500∘C.
