Tunnelling in metal-semiconductor contacts. I. Influence of the impurities

The effects of electron interactions on the tunnel current in metal-semiconductor contacts are studied in the framework of the latest theory set up by C Caroli et al. (1971). It is shown that interactions within the semiconductor appear only through a change of the density of states, at the interface, of the isolated semiconductor. The problem merely reduces to the study of the semiconducting electrode in the presence of interactions. Both intravalley and intervalley processes are considered. Whereas the former are shown to yield small corrections only to the tunnel current, the latter may, in some cases, result in a much higher current than the specular one. Numerical estimates strongly suggest that intervalley impurity scattering is responsible for the zero-bias finite conductance of p-n diodes made with germanium and for the huge discrepancy observed on M-n-GaSb contacts under high hydrostatic pressure.