Room temperature NO2 sensing properties of reactively sputtered TeO2 thin films

Tellurium oxide (TeO2) thin films were deposited on quartz substrates by sputtering a Te metal target in an Ar + O2 gas mixture. The structure and phase identification of the samples were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The as-deposited films were amorphous and became crystalline after thermal annealing at 500 °C. The optical energy gap of the films was determined from transmittance and reflectance spectra. The direct energy gap values were found to be 3.81 eV in as-deposited films and 3.73 eV in thermally annealed samples. Properties of the TeO2 thin films for NO2 gas sensing at room temperature were also investigated. The as-deposited films showed negligible sensitivity to NO2 gas. On the contrary the films prepared by thermal annealing showed a promising sensitivity and response towards tested gas.