Surface-sensitive conductance measurements on clean and stepped semiconductor surfaces: Numerical simulations of four point probe measurements

Recent progress in the development of microscopic four point probes permits surface-sensitive conductivity measurements on semiconductor surfaces. It is, however, not straightforward to extract the actual values for the surface and space-charge layer conductivity. Here we present an approach to data analysis which is based on numerical finite-element simulations. The results of such simulations are compared to the known analytical solutions for a collinear four point probe, and the approach is used to study the surface contribution to the conductivity of Si(1 1 1)(7 × 7). The procedure can also be used to study the influence of steps and other surface structures on the conductivity. This is illustrated by analysing the effect of mono-atomic steps on Si(1 1 1)(7 × 7). Finally, the potential benefits of collinear four point probe geometries with unequal contact spacings are discussed.