AVS 51st International Symposium
    Dielectrics Thursday Sessions
       Session DI+PS-ThA

Paper DI+PS-ThA10
STM, STS, and DFT Studies of SiO Deposition on the Ge(100) Surface

Thursday, November 18, 2004, 5:00 pm, Room 304B

Session: Oxides on Semiconductors
Presenter: T.J. Grassman, University of California, San Diego
Authors: T.J. Grassman, 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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To further the development of a germanium-based metal-oxide-semiconductor field effect transistor (MOSFET) a suitable gate-oxide material must be found which yields a high-quality, electrically-unpinned interface. For this, the semiconductor/oxide interface needs to be free of charge traps and other such interfacial defects that can cause Fermi-level pinning. High defect densities reduce the capacitance of the MOS structure and prevent the modulation of the semiconductor valence and conduction bands via the application of a gate bias. Germanium's intrinsic oxide has been shown to be inadequate for the task of providing a clean interface, therefore an alternative material must be used which can be deposited and grown on the Ge surface. To this end, we are investigating the bonding and electronic structure of the interface between SiO and the Ge(100)-p(2x1) surface using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and density functional theory (DFT) computational modeling. SiO can act as a precursor to SiO@sub 2@ or as a buffer layer for high-k dielectric growth. We will present atomically resolved images of both the clean Ge(100) and SiO-deposited surfaces at various coverages, along with DFT modeling results of the observed bonding structures. We find that SiO always bonds Si-end down, mostly inserting in between the Ge dimer rows and sometimes into the Ge dimers themselves. Even at modest coverages (> 5%) SiO bilayers are formed via pyramidal (SiO)@sub 3@ molecular structures with Si-O-Si-O bonding configuration. DFT-based STM simulations will be presented to aid in the interpretation of experimental STM images. We will also present STS dI/dV spectra of the associated surface electronic structure (density of states) which show that the SiO/Ge interface yields an unpinned Fermi level.