Electrical and optical properties of WO3 thin films

Tungsten trioxide (WO,) thin films were prepared by spray pyrolysis. The op tical and electrical properties of intensively colored films were studied. It was found that the near-infrared reflectivity increases in the colored s tate. This behavior is typical of degenerate semiconducting materials. Howe ver, the variations of the electrical conductivity with the temperature for these films, indicates semiconducting behavior, while the carrier concentr ation (n), measured by the Hall effect, is typical of degenerate material. The optical properties can be easily explained by the Drude theory, which i s related to the bulk properties of the samples. It is shown that the value of n is also related to the bulk proper-ties of the films, while the condu ctivity is controlled by the grain boundary effect. The results are interpr eted in terms of a modified version of Seto's model, taking into account th ermionic emission and tunneling of carriers through the potential barriers at the grain boundaries. (C) 2001 Elsevier Science B.V. All rights reserved .