Characterization of ultrasonic spray pyrolyzed tungsten oxide thin films

The ultrasonic spray pyrolysis (USP) technique has been employed to deposit tungsten oxide (WO3) thin films. The films were prepared by spraying 0.02 M ammonium metatungstate solution onto amorphous glass substrates kept at 250°C. These films were further annealed at 400°C for different time periods (1–5 h) in air. The films were characterized for structural, electrical and opto-electronic properties. X-ray diffraction technique was used to determine the crystallinity of the WO3 films and identify the phases that form as a function of annealing time. The as-prepared WO3 films were amorphous and crystallize when annealed at 400°C in air for 2 or more hours. From TEM, the grain size and lattice plane spacing are estimated. The films were further characterized by using time resolved microwave conductivity (TRMC) technique and decay time of the photogenerated charge carriers is calculated to be about 154 ns. The concentration and mobility of charge carriers are estimated from thermoelectric power (TEP) measurements.