Transient photoconductivity properties of tungsten oxide thin films prepared by spray pyrolysis

Tungsten oxide (WO3) thin films were deposited by spray pyrolysis of an ammonium tungsten oxide solution. The effect of postannealing on the structural, transport and optical properties of the films has been studied. Under steady-state illumination, slow photoconductivity growth and relaxation transients were observed at room temperature. The contributions of carrier concentration and mobility to the photoconductivity were determined from photo-Hall and photoconductivity data. The transient photoconductivity was found to be mainly due to photoinduced excess electrons over a wide time range from 0.0 to 10(4) s. This slow relaxation was characterized by two exponential decays indicating two discrete subband gap levels were involved. The fast photoconductivity relaxation over the time range from 10(-8) to 10(-1) s was more complicated and probably involved a distribution of subband gap states. (C) 2001 American Institute of Physics.