CONDUCTION MODELS IN GAS-SENSING SNO2 LAYERS - GRAIN-SIZE EFFECTS AND AMBIENT ATMOSPHERE INFLUENCE

A model for conduction that fits SnO2 polycrystalline layers with a grain size below 50 nm is presented. Quantitative evaluations using bulk parameters, found in the literature, and the assumption that surface oxygen vacancies are sites for atmospheric oxygen chemisorption permit a simple formulation of the problem: conduction by homogeneously distributed electrons along cylindrical filaments. An expression for the mobility is proposed, in which diffuse surface scattering is taken into account. On its basis, a relationship between the electrical mobility and the concentration of the reducing gas is theoretically derived for the first time. The predictions of the model for the dependence of conductance, concentration of conduction electrons and their mobility on the reducing-gas concentration are compared with experimental data and found to be in good agreement.