VIRTUAL CHARGE METHOD FOR ELECTROSTATIC CALCULATIONS IN METALLIC TIP AND SEMICONDUCTING SAMPLE SYSTEMS

We calculate the electrostatic field between a metallic tip and a semi conductor surface by replacing the electrodes by a set of virtual char ges, adjusted to fit the boundary conditions on the surfaces. The boun dary conditions on the semiconductor side of the surface are obtained by using the result of a direct integration of the Poisson equation. T he results of the method are compared to those given by a one-dimensio nal model. It is then applied to get some information which is useful in the theory of near field microscopy: Curvature of the energy bands at the semiconductor surface, influence of the tip shape, range of the electric field, effect of a dielectric insulating layer. (C) 1997 Ame rican Institute of Physics.