Transient photoconductivity measurements of ultrasonic spray pyrolyzed tungsten oxide thin films

Tungsten oxide (WO3) thin films were deposited onto amorphous glass substra tes by using the ultrasonic spray pyrolysis (USP) technique. A 0.02 M aqueo us ammonium metatungstate solution was pulverized, by means of an ultrasoni c metallic nozzle, onto the substrates maintained at 250 degrees C, The fil ms 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 fi lms with H+ ions from the H2SO4 electrolyte electrochemically. The crystall inity and structure of these films were determined by X-ray diffraction. Tr ansient photoconductivity measurements of these films in the microwave freq uency 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 a mplitude of TRMC signal on room temperature electrical resistivity of the s ample is described. (C) 2000 Elsevier Science Ltd. All rights reserved.