Conductivity of SnO2 thin films in the presence of surface adsorbed species

The influence of oxygen and/or ethanol vapors on the SnO2:Cu thin film conductance has been studied both in vacuum and in the air-based mixtures under the atmospheric pressure. We show that the dependence of the film conductance on the gas pressure can be approximated by the power low with a constant exponent only in a restricted range of pressure values. The film conductivity is discussed in the framework of electron adsorption theory suggesting that oxygen and ethanol create, correspondingly, acceptor-like and donor-like surface states in the energy gap of the oxide. We demonstrate that the gas-sensitivity of the fully depleted films may be successfully accounted for by the compensation of the semiconductor conductivity with surface impurities. The results of the calculations are in good agreement with our experimental data.