Space-charge capacitance of thin non-degenerate semiconductor films

Abstract

The problem of the space-charge capacitance of thin non-degenerate semiconductor films, whose thickness d is comparable with or smaller than the effective Debye length L D is discussed. The solution is based on the assumption that the properties of both the surfaces S1 and S2 are mutually dependent. It is shown that this dependence can be expressed by means of the ratio of d to L D and by the boundary conditions at both surfaces. If the interface at the surface S2 is formed by a semiconductor-metal structure, the surface S1 has only a negligible influence on the value of the surface potential V S2 in most real cases. However, if a semiconductor-dielectric structure exists at the surface S2, V S2 depends on the properties of S1 and the only constant parameters in this case are the density of all surface states at the surface S2 and their activation energies. Based on these considerations, an exact calculation of the space-charge capacitance of thin semiconductor films was made and from the results obtained some limiting cases were derived.