Formation of an electric dipole at metal-semiconductor interfaces

The insensitivity of experimentally observed Schottky barrier height (SBH) to the metal work function, a phenomenon known as Fermi level pinning, has traditionally been attributed to the presence of interface states in the band gap of the semiconductor. A recent theory showed that the polarization of the chemical bonds at metal semiconductor interfaces could quantitatively account for the experimentally observed strength of Fermi level pinning on different semiconductors, without regard to the actual distribution of gap states. This bond polarization theory thus provides a coherent explanation of the Fermi level pinning effect, on the one hand. and the experimentally observed dependence of the SBH on interface structure, on the other hand. The method used in this theory, the electrochemical potential equalization method hitherto employed only in molecular physics, and its limitations are here discussed in detail. especially in the context of application to solid interfaces. Similarities and differences between this theory and the metal induced gap state theory are also discussed.