Noncontact friction of a semiconductor with charge carriers of differing mobilities

The coefficient of noncontact friction as measured in an electric force microscopy experiment is computed for a semiconductor with positive and negative charge carriers of distinct mobilities. The friction is determined for a sample represented by classical electrodynamics coupled to diffusing carriers in a dielectric continuum. The analysis generalizes previous work in which positive and negative carriers were taken to have identical mobilities, allowing application to a wider range of semiconductors. Dielectric and electrical properties of the material are shown to be revealed by the dependence of the friction on experimentally accessible parameters such as probe-sample separation and carrier density.