Schottky barriers and band lineups at interfaces

Abstract

The principle concepts underlying our understanding of Schottky barriers for well-characterized interfaces are reviewed. The Tersoff ‘‘neutral point’’ picture based on metal-induced gap states seems promising but does not explain submonolayer results. The Tersoff band lineup model for semiconductors is tested by a Si–Ge heterojunction calculation. The difference between Si and Ge potentials is small enough to allow the junction potential to be decomposed into contributions from individual Ge planes in a Si matrix. Planes away from the junction lead to an ‘‘intrinsic’’ offset while those near the junction give a much smaller ‘‘junction sensitive’’ offset, justifying Tersoff’s assumption of an intrinsic process. A small change in the Schottky offset is strongly screened by a dielectric constant of order 10 as predicted by Tersoff. The offset is shown to be best understood using the principle of strict charge neutrality, emphasizing the irrelevance of interface dipoles as causing the offset. The offset is caused by the need to line up the hybrid energies (or neutral points) plus a correction of order 0.14 eV which compensates for the difference in bond strength between silicon and germanium.