Preparation and characterization of thallium(I) doped molybdenum heteropolyoxometalate semiconducting thin films

Thallium(I) doped molybdenum heteropolyoxometalate (HPOM) thin films were prepared using simple chemical bath deposition technique. These HPOM thin films were characterized for their optoelectronic, structural, morphological and compositional properties using UV–vis spectra, electrical resistivity, thermo-emf, TGA–DTA, XRD, SEM-EDAX data. XRD studies of HPOM material shows that the material is polycrystalline and having simple cubic spinel structure. UV–vis spectroscopy revealed that, thallium(I) doped molybdenum HPOM is a direct gap semiconducting material having band gap 2.5 eV. The dc electrical resistivity and thermoelectric power was measured in the temperature range of 27–270 °C. The variation of resistivity with respect to temperature showed that there is negative resistance region in the temperature range of 160–263 °C, indicating semiconducting nature of HPOM material. The thermoelectric power for the sample was positive over the whole range of the temperature showing that the HPOM material is p-type semiconductor. Compositional analysis (EDAX) of samples shows the Tl(I) is intercalated in phosphomolybdate anion. The TGA–DTA data revealed that the molybdenum HPOM sample is thermally stable up to 286.04 °C.