Two-dimensional currents at semiconductor surfaces as resonances within the classical current equation

Logarithmic voltage profile characteristic to two-dimensional current flows has been reported for several semiconductor surfaces. We analyse this phenomenon within a simple model of accumulation and inversion layers. Prompted by numerical analysis of several conductivity profiles we point out how the logarithmic voltage drop may appear in the case of three-dimensional samples. It may or may not be observed both for the accumulation and the inversion layers. Further, the numerical data suggest that the surface conductivity at large distances is governed by very few parameters.