AVS 50th International Symposium
    Surface Science Friday Sessions
       Session SS2-FrM

Paper SS2-FrM4
Understanding Fermi Level Pinning of SiO on GaAs(001)-(2x4)

Friday, November 7, 2003, 9:20 am, Room 328

Session: Oxide Surfaces and Interfaces
Presenter: D.L. Winn, University of California, San Diego
Authors: D.L. Winn, University of California, San Diego
M.J. Hale, University of California, San Diego
A.C. Kummel, University of California, San Diego
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Scientists have been trying to develop a metal oxide semiconductor field-effect transistor (MOSFET) with GaAs in an effort to reduce standby power and gate leakage. In order to fabricate this device, it is important to understand the chemistry and physics at the oxide/semiconductor interface. It has been reported that a common cause of Fermi level pinning is the liberation of As, resulting from oxides bonding to Ga atoms on the surface. This has been directly observed using STM to monitor the reactions of O and O@sub 2@ on GaAs(001)-(2x4). In contrast, we have shown that SiO pins the Fermi level but does not liberate As when it is deposited on the GaAs(001)-(2x4) surface. Scanning tunneling microscopy (STM) images show that SiO inserts into the As dimers. SiO bonds in both trough and row dimers with a very small minority of the SiO molecules inserting into As-Ga backbonds. Using scanning tunneling spectroscopy (STS), we have observed that ~5% of a monolayer of SiO pins the Fermi level on GaAs(100)-(2x4) at mid-band gap. This is consistent with the SiO absorbates withdrawing charge from the surface As atoms, causing charge on the As atoms to grossly deviate from the charge on bulk As atoms.