INTERFACE STRUCTURE AND SCHOTTKY BARRIERS AT EPITAXIAL SI(111)/PB INTERFACES

Two different epitaxial Si(111)/Pb interfaces can be prepared, i.e. a metastable interface with a (7 x 7) and a stable interface with an incommensurate but close to (square-root 3 x square-root 3)R30-degrees surface unit cell. Schottky barrier heights of diodes made by depositing thick Pb layers on these interfaces are very dependent on the structure at the interface (0.70 and 0.93 eV for the (7 x 7) and square-root 3 x square-root 3)R30-degrees type interfaces respectively). In particular the second value is very exceptional for metal-silicon contacts. Even higher values were found from shifts in photoelectron spectra of Si covered with one ML (0.94 and 1.04 eV respectively). Evidence from ARUPS data indicates that the corresponding pinning level is associated with a discrete interface state in a common gap of Pb and Si.