Growth, structural, electrical and optical properties of the thermally evaporated tungsten trioxide (WO3) thin films

Tungsten trioxide (WO3) thin films are of great interest due to their enormous and promising applications in various opto-electronic thin-film devices. We have investigated the structural, electrical, and optical properties of the WO3 thin films grown by thermal evaporation of WO3 powder and their dependence on growth condition. The WO3 thin films were grown on glass substrates at different substrate temperature varying from room temperature to 510 °C. The structural characterization and surface morphology were carried out using X-ray diffraction and atomic force microscopy, respectively. The amorphous films were obtained at substrate temperatures below 450 °C whereas films grown above 450 °C were crystalline. The surface roughness and the grain size of the films increase on increasing the substrate temperature. The electrical characterization has been carried out using four-point-probe methods. The resistivity of the films decreases significantly while the carrier concentration and mobility increase with the substrate temperature. The transparency and optical energy band-gap, Eg, of the films are found to decrease monotonically as the substrate temperature increases.