Boron Doped ZnO Films Deposited by DC Reactive Sputtering Using Zn:B Target: Influence of the Deposition Temperature on the Structural, Electrical and Optical Properties

Abstract

ZnO-based transparent and conducting oxides (TCOs) are commonly used as a window layer in thin-film solar cells. However, TCOs with high transparency in the visible and near-infrared parts of the electromagnetic spectrum, plus excellent electrical properties are required in this application. In this study, TCOs based on ZnO:B films deposited by DC reactive sputtering using Zn:B alloy target were investigated. The impact of deposition temperature on the growth and physical properties of the films was examined. Structural, optical and electrical properties of these films were investigated by means of x-ray diffraction (XRD), Ultraviolet-Visible-Near Infrared (UV-VIS-NIR) spectroscopy, and Hall effect measurement, respectively. The XRD analysis revealed that all films are of hexagonal wurtzite structures, with a preferred orientation along the c-axis. The optical spectroscopy results indicated that all the ZnO:B films had optical transparency above 90% in the visible region which then slightly decreased in the near-infrared region. The highest carrier concentration, conductivity, and mobility were obtained at the deposition temperature of 300 °C–due to improvement in crystal growth–while higher temperatures slightly deteriorated the electrical properties, possibly due to a slight decrease in the crystallite size.

Keywords: ZnO; Transparent and conducting oxides; ZnO:B, DC reactive sputtering; deposition temperature