AVS 51st International Symposium
    Semiconductors Wednesday Sessions
       Session SC-WeA

Paper SC-WeA10
An Atomic Understanding of the Sub-Monolayer Interface formed Upon the Deposition of SiO on GaAs(001)-c(2x8)/(2x4)}

Wednesday, November 17, 2004, 5:00 pm, Room 304C

Session: Narrow Gap Semiconductors
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
J.Z. Sexton, University of California, San Diego
M. Passlack, University of California, San Diego
A.C. Kummel, University of California, San Diego
Correspondent: Click to Email
Scientists have been trying to develop a GaAs-based MOSFET device in an effort to reduce standby power and gate leakage. To achieve this it is important to understand the chemistry at the oxide/semiconductor interface. The interface formed upon deposition of SiO on GaAs(001)-c(2x8)/(2x4) was studied using STM, scanning tunneling spectroscopy (STS) and DFT. STM images show that SiO molecules bond Si end down in three distinct locations: into row and trough As dimers and between row As dimers. It was also observed that when SiO bonds between row As dimers, the two adjacent dimers along the [1bar10] direction each contain an inserted SiO molecule forming a chain of three molecules (triple site). STS measurements show that ~5% of a monolayer of SiO pins the Fermi level at mid gap. This is consistent with SiO absorbates withdrawing charge from surface As atoms, causing charge on the As atoms to grossly deviate from the charge on bulk As atoms. Multiple SiO sites were simulated using DFT, the lowest energy structure however was not observed in STM. An energy versus chemical potential plot was used to explain and identify the most stable bonding structures in the coverage studied with STM. This plot showed that at low SiO coverages the most stable sites were single sites but at higher coverages the most stable sites shifted to sites involving three SiO molecules including the triple site. This work demonstrates the key role of coverage in determining the most stable bonding structure. For oxides on semiconductors there are usually multiple nearly degenerate bonding configurations and the coverage is the key variable in determining the relative chemical potentials