Low-temperature alkali metal/III–V interfaces: A study of metallization and Fermi level movement

Abstract

The interfaces of alkali metals (Cs and Rb) on GaAs and InP(110) surfaces prepared at 110 K low temperature have been studied using photoemission. At low temperature, multilayers of alkali metals with laminar growth can be obtained. The overlayer metallization is investigated by following the density of states near the Fermi cutoff, the free electron plasma loss, and the Fermi level movement at the semiconductor surfaces. Several criteria of metallicity are proposed. It is found that one monolayer of Cs or Rb is not metallic, and full metallicity is established at around two monolayers of coverage. The Fermi level movement relative to the semiconductor band edges as a function of alkali metal coverage has been closely followed. The semiconductor band bendings at low coverages are attributed to the surface-donor states originating from alkali metal atom chemisorption. The Fermi level stabilization at these interfaces occurs when the overlayers become metallic. This pinning behavior is explained in terms of the metal-induced gap states. The Fermi level pinning at the room temperature interfaces is also discussed and compared with the low-temperature behavior.