Effects of annealing on morphological, structural and electrical properties of thermally evaporated WO3 thin films

Tungsten trioxide (WO3) thin films were prepared by thermal evaporation method onto quartz substrates at room temperature. Effect of annealing temperature (from 200 to 800 °C) to morphology, crystallographic structure and electrical properties were investigated. In order to investigate the temperature dependant resistivity properties of the films dark current–voltage measurements were done at the temperatures of 30, 60, 90, 120 and 150 °C. From the AFM pictures it is seen that the increasing annealing temperature causes an increase in grain sizes. At elevated temperatures the grains combine to each other and thus form continuous and homogenous surfaces. From the XRD patterns it was seen that the as-prepared and annealed films at 200, 300, 310 and 320 °C were amorphous. On the other hand at 330 °C and higher temperatures the films were found as in crystallized structures (monoclinic phase). From the current–voltage measurements it was seen that the contacts areohmic and the current increased with increasing temperatures. From the calculated values it was seen that the produced films shows good semiconducting nature.

► Grain size increased significantly with increasing annealing temperature.
► Films with annealing temperature of color change have occurred.
► The transition from amorphous structure to crystal structure has occurred in 330 °C.
► Resistance values associated with temperature measurement changed in between 106 and 1011 Ω.