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[Formula: see text]C to 500[Formula: see text]C. ZnO thin films were deposited on glass substrates via ultrasonic spray technique with 0.2[Formula: see text]mol/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[Formula: see text]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 3.245[Formula: see text]eV to 3.281[Formula: see text]eV with increasing substrate temperature of 250–500[Formula: see text]C. The observed Urbach energy of ZnO thin films decreases from 0.11311[Formula: see text]eV to 0.04974[Formula: see text]eV. At a high temperature, the electrical conductivity of ZnO films was increased from [Formula: see text] to 41.58 ([Formula: see text].cm)[Formula: see text] with the increasing substrate temperature from 350[Formula: see text]C to 500[Formula: see text]C.