Adsorption and growth of Sn on Si(100) from synchrotron photoemission studies

Abstract

Photoemission spectroscopy was used to study the initial growth and interaction of Sn on Si(100). The as-deposited surfaces were annealed at about 550 °C, generating the following coverage-dependent reconstructions: c(4×4), (6×2), c(8×4), and (5×1). Changes in the Si 2p core-level line shape were identified as the selective modification of Si surface dimer atoms by the presence of Sn adatoms. A relative measure of the Sn-adatom–Si-substrate interaction is presented by quantification of the average number of Si surface sites modified in the presence of a Sn adatom for various coverages. The Sn 4d core-level spectra revealed two components for Sn coverages below 1 monolayer (ML), indicating the existence of two inequivalent Sn sites, whose relative occupancy is seen to vary with coverage. The Sn 4d core level for the majority sites roughly follows the movement of the Fermi level within the band gap of Si for increasing Sn coverages, while that for the minority sites remains at a constant binding energy relative to the Si valence-band maximum. Implications concerning the structure of the Sn overlayer are discussed. The Sn-induced band bending and the Schottky barrier height are obtained. Photoemission from the valence bands near the Fermi level shows that the Sn-covered Si(100) surface has little density of states at the Fermi level for coverages below 1 ML.