title: Direct and indirect causes of Fermi level pinning at the SiO/GaAs interface.
abstract: The correlation between atomic bonding sites and the electronic structure of SiO on GaAs(001)-c(2x8)/(2x4) was investigated using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and density functional theory (DFT). At low coverage, STM images reveal that SiO molecules bond Si end down; this is consistent with Si being undercoordinated and O being fully coordinated in molecular SiO. At approximately 5% ML (monolayer) coverage, multiple bonding geometries were observed. To confirm the site assignments from STM images, DFT calculations were used to estimate the total adsorption energies of the different bonding geometries as a function of SiO coverage. STS measurements indicated that SiO pins the Fermi level midgap at approximately 5% ML coverage. DFT calculations reveal that the direct causes of Fermi level pinning at the SiO GaAs(001)-(2x4) interface are a result of either local charge buildups or the generation of partially filled dangling bonds on Si atoms.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: Darby L
authors.initials: DL
authors.lastname: Winn
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Hale
authors.forename: Tyler J
authors.initials: TJ
authors.lastname: Grassman
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Kummel
authors.forename: Ravi
authors.initials: R
authors.lastname: Droopad
authors.forename: Matthias
authors.initials: M
authors.lastname: Passlack