Computational approach for the chemical sensitivity of oxide and sulphide semiconductor surfaces

A short survey is given of our computational approach for the study of the chemical surface sensitivity of some oxide and sulphide semiconductors. Many oxides and sulphides behave as n-type semiconductors with donors originating from nonstoichiometric defects. Therefore, n-type semiconductors with negligible hole concentrations are considered here. Chemical activity of n-type semiconductor surfaces is based on adsorbate interactions both with conduction-band bulk electrons and with localized electrons trapped at surface states. Some effects may also origin from a possible ionic response of the semiconductor to changing internal electric fields. A dynamical approach with expressions similar to those for the generation-recombination processes (Schockley-Hall-Read theory) is used to describe adsorbate interactions with conduction-band bulk electrons. As practical examples we consider SnO₂(110) - 1 × 1 and wurtzite CdS(1010) - 1 × 1 surfaces, both being the most stable faces of their structures, respectively, and nonpolar in the bulk derived geometry. With the SnO₂(110) surface we use clusters in calculations of localized electronic surface states originating from different defects, while a slab method is used to calculate the atomic relaxation at the CdS(1010) surface.