The image-force effect at a metal-semiconductor contact with an interfacial insulator layer

The theory of image-force lowering of the potential barrier at a metal-semiconductor contact has sometimes been incorrectly applied to the metal-insulator-semiconductor system. In this paper the image-force potential is derived for a finite-thickness insulator bounded by a metal at one side and another insulator (or semiconductor) at the other side. The exact solution corresponds to an infinite series of images of the electron with respect to both interfaces. If the interfacial insulator permittivity is lower than that of the semiconductor, then the image force in the vicinity of the insulator-semiconductor interface will pull the electron away from the metal.