MECHANISMS OF BARRIER FORMATION IN SCHOTTKY CONTACTS - METAL-INDUCED SURFACE AND INTERFACE STATES

Metal as well as nonmetal adatoms are generally inducing surface states and dipoles on semiconductor surfaces. Both effects may be understood in a bond picture, which describes adatom-substrate bonds in a surface-molecule model, and in the band picture, which considers the tailing of adatom electron wave functions into the semiconductor. These two approaches have in common a charge transfer between the adatoms and the substrate which may be modeled by the difference of their electronegativities. The same concept may be applied to metal-semiconductor contacts. In that energy range, where the metal conduction band overlaps the semiconductor band gap, metal electron wave functions are tailing into the semiconductor and a charge transfer occurs between the respective continuum of metal-induced gap states (MIGS) and the metal. Deviations of barrier heights in Schottky contacts from what is predicted by that MIGS-and-electronegativity concept are attributed to fabrication-induced defects of donor type or interface strain. © 1989.