Transient photoconductivity measurements of ultrasonic spray pyrolyzed tungsten oxide thin films

Tungsten oxide (WO3) thin films were deposited onto amorphous glass substrates by using the ultrasonic spray pyrolysis (USP) technique. A 0.02 M aqueous ammonium metatungstate solution was pulverized, by means of an ultrasonic metallic nozzle, onto the substrates maintained at 250 degrees C, The films were further annealed at 400 degrees C for various time periods (1, 2, 4, and 6 h). HxWO3 films were formed by intercalating the as-prepared WO3 films with H+ ions from the H2SO4 electrolyte electrochemically. The crystallinity and structure of these films were determined by X-ray diffraction. Transient photoconductivity measurements of these films in the microwave frequency range were performed using the time-resolved microwave conductivity (TRMC) method. From TRMC measurements, the decay time of the photogenerated charge carriers was estimated and the mechanism of the decay processes was correlated with the film composition and structure. The dependence of the amplitude of TRMC signal on room temperature electrical resistivity of the sample is described. (C) 2000 Elsevier Science Ltd. All rights reserved.