AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM7
Atomistic Mechanisms of Fermi-level Pinning at the Oxide-Semiconductor Interface

Wednesday, November 5, 2003, 10:20 am, Room 328

Session: Adsorption on Semiconductor Surfaces
Presenter: J.Z. Sexton, University of California, San Diego
Authors: J.Z. Sexton, University of California, San Diego
M.J. Hale, University of California, San Diego
D.L. Winn, University of California, San Diego
M. Passlack, Motorola Inc.
A.A. Demkov, Motorola Inc.
A.C. Kummel, University of California, San Diego
Correspondent: Click to Email
Understanding the mechanism of Fermi-level pinning is critical in the development of an electronically passive oxide - III/V semiconductor interface. This insulator-semiconductor interface is important in the development of a practical of III / V MOSFET technology. We have observed Fermi-level pinning and un-pinning in STM and STS at the GaAs(001)-2x4 surface in three cases, upon sub-monolayer a) deposition of oxygen atoms, b) vapor deposition of Ga@sub 2@O and c) vapor deposition of In@sub 2@O. We have seen that the oxide layer formed upon atomic oxygen exposure forms a pinned interface. However, when a vapor deposited gallium oxide layer is formed, the surface remains unpinned. When In@sub 2@O is vapor deposited on the GaAs-2x4 surface, several bonding structures are formed, ultimately leading to a pinned interface. We have identified the bonding structures using first-principles calculations and have identified the mechanism for Fermi-level pinning for all the cases listed above. The Fermi-level pinning in case a) is due to a deep-level state, caused by significant charge withdrawal from the gallium atoms by oxygen. The Fermi-level unpinning in case b) is due to the bonding configuration resulting in a geometrically favorable and charge balanced structure. The Fermi-level pinning in case c) is dependent on the specific structure observed in STM. We have done calculations to elucidate the bonding and electronic structure of the observed bonding configurations and have observed that some structures are pinned and some are unpinned. We have seen two types of Fermi-level pinning: 1) deep level pinning caused by a fixed interface atomic state in the band-gap region and 2) a dipole-like pinning that is distributed over the covalent bonding network which induces states on the valence and conduction band edges. In summary, the bonding structure at the interface determines the existence and type of Fermi-level pinning.