The effect of DC power and annealing on the structural, optical, and electrical characteristics of sputtered amorphous WOX thin films

Abstract

Tungsten oxide (WOX) is considered as one of the promising materials due to its unique properties in widespread optoelectronic and photonic applications. This study reports on the deposition of WOX thin films via reactive magnetron sputtering technique with various low DC power and constant sputtering pressure at room temperature. XRD results reveal that an amorphous state for all the as-deposited films, while annealed films at 650 °C have WO3 monoclinic structure. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies indicate all as-deposited films have a dense, homogeneous, and quite smooth surface with a root-mean-square roughness (σRMS) below 1 nm. Annealing significantly affects film morphology, the formation of large grains and increasing the surface roughness. Optical parameters were examined by ultraviolet–visible (UV–Vis) spectrophotometer. Increasing sputtering power leads to a decrease in transparency value, an increase in absorbance, a reduction in penetration depth, a red shift of the fundamental absorption edge, and a reduction in the band gap energy from 3.06 eV to 2.61 eV. The annealed films exhibit a smaller optical band gap compared to as-deposited films in the range of 2.44 eV–2.93 eV. The temperature dependence of the sheet resistance corresponds to the Arrhenius law for as-deposited films with DC power of 10 W–30 W, indicating semiconducting nature. A decreasing trend in activation energy (0.283–0.055 eV) was observed with increasing DC power. All the annealed films exhibit insulator nature with a resistance of more than 100 MΩ. Analysis of these results suggests that the desired structural, optical, and electrical properties can be achieved by controlling deposition conditions.