Computational approaches to the chemical sensitivity of semiconducting tin dioxide

Some computational approaches to the chemical sensitivity of semiconducting tin dioxide are presented. Chemical sensitivity is often observed using conductance measurement. Therefore, the potential energy barriers in grain contacts between adjacent grains of a polycrystalline semiconductor are the key parameters for transducing the chemical surface sensitivity into the conductance response. The rate equation model describes the electronic exchange between the adsorbed oxygen species and the bulk conduction band of a semiconductor. It predicts the type of the major negative oxygen ion (O-2(-) or O-) at the surface as a function of temperature in agreement with experimental findings. The grain geometry has only a small effect on the potential energy barrier at the surface of finite grains. Even a small neck contact between grains, in the case of mobile donors, decreases strongly the potential energy barrier between grains compared to that in the case of an open grain contact. Results from Monte Carlo simulations with random barrier networks reveal that the current-voltage characteristic of a polycrystalline semiconductor is non-linear at higher voltages and the non-linearity of the network increases with increasing width of the barrier distributions. Electronic-structure calculations with clusters give qualitative information on the role of oxygen vacancies in different atomic planes in SnO2 and its unrelaxed and unreconstructed (110) surface. (C) 1998 Elsevier Science S.A. All rights reserved.