1.3.5 Conduction Mechanism in Undoped and Antimony Doped SnO2 Based FSP Gas Sensors

14th International Meeting on Chemical Sensors - IMCS 2012
2012-05-20 - 2012-05-23
Nürnberg/Nuremberg, Germany
1.3 Metal Oxide-based Gas Sensors I
J. Rebholz, C. Jaeschke, M. Hübner, U. Weimar, N. Barsan - Institute of Physical and Theoretical Chemistry, Tübingen University (Germany), D. Pham, L. Mädler - IWT Foundation Institute of Materials Science, University of Bremen (Germany)
105 - 108


The conduction mechanism in highly porous thick film SnO2 sensing layers, obtained by a direct deposition technique using FSP (Flame Spray Pyrolysis), and the influence of different antimony (Sb) doping levels on the electrical properties of the host material is investigated by simultaneous DC electrical resistance and work function changes measurements in various ambient atmospheres. The situation in the case of the undoped FSP-sensors is very similar to the results obtained on polycrystalline thick film layers: we found a seamless transfer of the conduction mechanism from a depletion layer controlled one to the flat band situation and to an accumulation layer controlled one. The switch between these two models directly occurs in the absence of ambient oxygen, indicating that the depletion region is only determined by its adsorption. The degeneration of the semiconductor, in the case of the accumulation layer controlled conduction mechanism, is not observed. The addition of Sb influences the conduction mechanism dramatically due to its effect on the bulk concentration of free charge carriers. In contrast to the undoped FSP-SnO2 sensor there is a direct switch from a conduction mechanism controlled by the depletion layer to the degenerate semiconductor situation that indicates a deep crossing of the Fermi level into the conduction band; moreover an initial upward band bending is observed.