Electronic states and Schottky barriers at Pd 2Si/Si(111) interfaces

Abstract

It is possible to account for measured Pd/Si Schottky barrier heights (0.71-0.73 eV) by assuming that the interface between Si and Pd 2Si includes a hexagonal Si transition region induced by the presence of Pd impurities. With the Fermi level pinned slightly above the Si valence band edge by hydridized PdSi states at the interface, as calculations indicate, the Schottky barrier height is determined primarily by the band gap of hexagonal Si, which is about 0.85 eV. Since Pd atoms are larger than Si atoms, isolated substitutional and interstitial Pd atoms are not readily incorporated into the Si lattice. We believe that the Pd impurities form triangular clusters at Si vacancies. Since these clusters are more easily accommodated in hexagonal than in cubic Si, the Si stacking sequence changes from cubic to hexagonal, giving rise to the transition region.