CHEMISORPTION EFFECTS ON THE THIN-FILM CONDUCTIVITY

An investigation of chemisorption effects on the electrical conductivity of thin, wide bandgap semiconductors is presented in the framework of the Volkenstein model. The controversially discussed problem of a neutral, weak-chemisorbed state is reconsidered on the basis of the one-electron theory of chemisorption (considered by Einstein and Schrieffer). An analytically tractable variational method is developed for the ground state in lattice space. It turns out that in case of atop-anion binding a stable, weak-chemisorbed state can arise. For the case of acceptor-like chemisorption the pressure dependence of the thin-film conductivity is derived, solving selfconsistently the one-dimensional Poisson equation. In a wide pressure region the conductivity shows a power-law behaviour. It is found that the power is determined by different, fundamental parameters and cannot be expressed by only one parameter, e.g., the constant, stochiometric exponent in the mass-action law. Furthermore, the theoretical values of the power vary between 0 and 1 in agreement with the variety of experimental results.