Hall Coefficient Determination and Electrical Properties of Chemical Bath-Deposited n-WO3 Thin Films

Nanocrystalline and porous chemical bath-deposited n-WO3 thin films at low temperature (318 K) are reported. The high-quality and well-reproducible films have been fabricated by acidic hydrolysis of tungstate ion followed by thermal annealing at 573 K for 1 h. X-ray diffraction analyses of the deposited WO3 films revealed that they were amorphous. However, an amorphous-to-crystalline transition with monoclinic phase was observed. Atomic force microscopy (AFM) analyses revealed a homogenous but irregular cluster of faceted spherically-shaped grains with pores. Scanning electron microscopy corroborated the AFM results. The optical absorption analysis of WO3 film showed that direct optical transition exists in the photon energy range 3.00–4.00 eV with bandgap of 3.70 eV. The refractive index developed peak at 315 nm in the dispersion region while the high frequency dielectric constant ɛ ∞, and the carrier concentration to effective mass ratio, N/m*, were found to be 1.37 and 1.45 × 1039 cm−3, respectively. The temperature dependence of the electrical resistivity of the deposited films follows the semiconductor behavior with thermal activation energy of 2.0 meV, while the Hall coefficient R H was determined to be 0.17 cm3/A s.