Br doping effect on structural, optical and electrical properties of ZnS thin films deposited by ultrasonic spray

Abstract

In this study, we report the influence of Bromine (Br) doping levels on certain Zinc Sulphide (ZnS) thin films physical properties. Br doped ZnS films were deposited on glass substrates using ultrasonic spray method with a varied Br concentration from 0% to 2% to investigate its incorporation effect and identify the accurate doping amount. The Br-doped ZnS thin films exhibit an obvious improvement on its electrical, structural and optical properties. The obtained results indicated that low doping percentage has a crucial effect on the grown Br-ZnS films. The structural, morphological, optical and electrical properties of the as prepared films were investigated by various techniques of characterization including X-ray diffraction (XRD), SEM, UV–Vis-NIR spectrophotometer as well as the electrical measurements via the four-probe technique. The XRD analysis pattern confirms that prepared films were polycrystalline with co-existence of cubic and hexagonal phases. The average crystallites size decreases from 61.5 to 26 nm with increasing Br incorporation in ZnS films. The scanning electron microscopy images (SEM) revealed that the surface morphologies are characterized by an apparent increase of roughness and good homogeneity. Moreover, the film thickness increases from 181 to 270 nm after Br doping. The films transparency exhibits a maximum value of 76% in the visible region, which decreases with increasing Br concentration in the material. The direct band gap values have been determined from the transmittance spectra, and these values increase in the optic band gap region (3.5–3.8 eV) with the increase of Br concentration. The electrical measurements reveal that films have a resistivity varying between 2.5 × 103 and 3.1 × 104 Ω.cm with increasing Br content. We concluded that 0.5% Br-doping ratio improves the ZnS physical properties and rends it suitable for optoelectronic devices fabrication.