Charge carrier transport in nanocrystalline SnO2 thin film sensor and temperature dependence of toxic gas sensitivity

Charge carrier transport studies of nanostructured SnO2 thin films have been carried out using DC conductance and AC impedance studies. DC conductance variation with temperature (26-125 degrees C) follows Arrhenius type thermally activated carrier transport relation. Multifrequency impedance studies in the temperature range studied indicated the contribution from ionic conductance in addition to the band gap conduction. Grain boundary resistance as a function of frequency shows that the ionic species plays a major role at lower temperatures. Temperature dependent impedance studies carried out under vacuum also suggests the dominance of surface adsorbed ionic species in presence of air at room temperature. Higher conductivity observed at higher temperatures is due to the combined effects of thermally assisted carrier generation and increased diffusion rate of ionic species at the grain boundaries, though the contribution due to the latter decreases with an increase in temperature. The gas sensitivity studies of nanocrystalline SnO2 film sensor towards toxic gases such as SO2 and H2S showed decrease with increase in temperature. The sensitivity decrease at higher temperatures could be explained based on the relatively less change in current occurring with toxic gas interaction due to lower concentration of surface adsorbed oxygen species. Lesser sensitivity at higher temperatures is mainly due to decrease in the adsorbed oxygen species resulting from an increase in the desorption rate from the SnO2 surface. (C) 2016 Elsevier B.V. All rights reserved.