Surface spectroscopy of Schottky-barrier formation on Si(111) 7 × 7: Photoemission studies of filled surface states and band bending

Abstract

The formation of Schottky barriers between Si(111) 7 \ifmmode\times\else\texttimes\fi{} 7 and group-III metals has been studied by ultraviolet photoemission spectroscopy. Modifications of the band bending and of the work function occur for low values of metal coverage (one to four monolayers). The "intrinsic," clean surface states are simultaneously replaced with "extrinsic" metal-related interface states. A two-step empirical model is proposed for the formation of the barrier. The first step is saturation of interface bonds, and the second step, critical in determining the junction properties, corresponds to the formation of a thin region with properties intermediate between that of a metal and of a semiconductor. Our experiments emphasize the need for a detailed theoretical treatment of the interface chemical bonds and underline the inadequacy of "macroscopic" models for metal-semiconductor junctions.