IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Monday Sessions
       Session SC+SS-MoM

Paper SC+SS-MoM7
Displacement of Surface As Atoms by Insertion of Oxygen Atoms into As-Ga Backbonds

Monday, October 29, 2001, 11:40 am, Room 122

Session: Oxidation of Semiconductors
Presenter: M.J. Hale, University of California, San Diego
Authors: M.J. Hale, University of California, San Diego
S.I. Yi, University of California, San Diego
J.Z. Sexton, University of California, San Diego
A.C. Kummel, University of California, San Diego
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Stable and metastable oxide structures resulting from the reaction of GaAs(001)-(2x4) with O and O@sub 2@ are investigated using scanning tunneling microscopy (STM). The relative stability of these oxide structures is examined using density functional calculations. STM images show that when GaAs(001)-(2x4) is exposed to O atoms, the O atom will either remove an As atom from its original dimer position and take its place or insert into an As-Ga backbond and create a metastable state. As the O atom coverage increases, O atoms increasingly occupy the position of two As atoms across two neighboring dimers, while the number of metastable states remain constant. These experiments show that As is preferentially removed as a pair (As@sub 2@) with one removed As atom originating from each of two neighboring As-As dimers instead of two As atoms from the same As-As dimer. This displacement of As@sub 2@ is consistent with the propensity of the unit cell to relax into a charge-balanced morphology. Furthermore, the charge-imbalance from oxygen chemisorption is the driving force for As@sub 2@ displacement. DFT calculations demonstrate both the charge imbalances in the metastable states and the relative stability of the final chemisorption state. The displaced arsenic atoms form As@sub Ga@ antisites which pin the Fermi level and prevent thermal oxidation from forming an electrically passive interface on GaAs in contrast to vapor deposited oxides.