Modeling electrostatic scanning force microscopy of semiconductors

A model is presented for the electrostatic interaction between the tip of a scanning force microscope and the surface of a semiconductor in condition of depletion. By representing the tip as a conducting sphere and suitably approximating the semiconductor space-charge region, analytical expressions are derived for the boundary of this region and the tip-sample capacitance and force. Operation in an immersion medium with high dielectric constant is found to enhance the doping sensitivity of the electrostatic force. As a function of the tip-sample distance, this force exhibits a zero point, if the permittivity of the immersion medium exceeds that of the semiconductor.