Epitaxial growth and electronic structure of lanthanide silicides on n-type Si(111)

Abstract
We present an investigation of Gd, Dy, Er, and Lu silicides epitaxially grown on n-type Si(111) using scanning-tunneling microscopy, low-energy electron diffraction, and core-level photoemission. With varying silicide film thickness, we observe structurally, electronically, and chemically different silicide phases. In particular we found that the Si-2p photoelectron spectra from monolayer silicides are different from those at higher coverages. This observation is attributed to the structure of the layered hexagonal silicide, with a Si vacancy lattice only present in case of multilayer films. Furthermore, we observe peculiar electronic properties: An extremely low band bending is found in the monolayer range, with a Fermi-level position of only 0.08±0.05 eV below the conduction-band minimum of silicon, representing the lowest value ever observed on n-type silicon. With increasing coverage, a final Schottky-barrier height of 0.32±0.05 eV is obtained. This behavior is interpreted as a consequence of the developing metallicity of the silicide overlayer and will be discussed in the framework of theoretical models for Schottky-barrier formation.