Minority carrier effects in nanoscale Schottky contacts

We report the current-voltage behavior for nanoscale point contacts to Si(111) obtained in ultrahigh vacuum using scanning tunneling microscopy. Epitaxial CoSi₂ islands provide single-crystal contacts with well-defined size and shape. The zero bias conductance is found to be independent of the island size (10²-10⁴nm²) and shape, but varies strongly with the surface Fermi level position. This behavior is explained by the recombination-generation current from minority carriers at the free surface, which may be orders of magnitude larger than the majority carrier thermionic or tunnel currents across the contact interface. This can give rise to large shifts of the apparent ideality factor and Schottky barrier height for the point contact.