Extended wide band gap amorphous zno thin films deposited by spray pyrolysis

Abstract

In this work, the ZnO thin films were deposited on substrates heated in a temperature varied between 250 to 400°C with a step of 50°C. The solution used for this deposition is composed of methanol and Zinc acetate. The XRD analysis confirmed that the deposited ZnO thin layers have a hexagonal wurtzite high quality with a preferential orientation (100) a-axis perpendicular to the substrate. The crystallite size is calculated using the Debye-Scherrer formula, the latter varies between 32-61 nm. Analysis by UVVisible spectrophotometer is an important characteristic to assess the quality of the deposited layers. The prepared samples showed a high transmission which is higher than 82% in the UV-Vis region and also observed the presence of two phases leading to two different optical band gaps for substrate temperature at 250 and 300°C. The direct optical band gap energy calculated from the transmittance spectra was decreased with augmentation of substrate temperature. The minimum value of Urbach energy of ZnO thin film was achieved with 400°C. The measured contact angles are less than 90° for all the prepared samples confirming the hydrophilic character of all the films. The conductivity was ranged from 0.025 to 1.033 (Ωcm)-1 with increasing Ts.