AVS 49th International Symposium
    Thin Films Friday Sessions
       Session TF-FrM

Paper TF-FrM9
Chemical Bonding Requirements for Forming Passive Semiconductor Oxide Interfaces

Friday, November 8, 2002, 11:00 am, Room C-101

Session: Fundamentals of Thin Flm Growth
Presenter: A.C. Kummel, University of California, San Diego
Authors: J.Z. Sexton, University of California, San Diego
A.C. Kummel, University of California, San Diego
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The formation of passive, electronically unpinned metal oxide - semiconductor interfaces is a critical part in the development of III / V MOSFET technology. A high quality gate oxide will unpin the Fermi level and will form an interface with low interfacial defect densities. We have done first-principles density functional theory calculations to investigate the chemical bonding requirements for forming a passive gate-oxide / semiconductor interface. Upon MBE deposition onto the GaAs(001)- @beta@2(2x4) surface, Ga @sub 2@O inserts into a pair of surface As-dimers. This layer unpins the Fermi level and allows for growth of bulk amorphous oxide. This is in contrast to O@sub 2@ chemisorption which displaces surface arsenic atoms and pins the Fermi level. First principles calculations were done to elucidate the mechanism for Fermi level unpinning on this surface. Calculations comparing Ga@sub 2@O and O@sub 2@ chemisorption on GaAs(001)- @beta@2(2x4) indicate that the requirements for the formation of a passive interface are: 1) charge balance restoration of surface As atoms to near-bulk values, 2) restoration of surface geometry to a bulk-like bonding environment, and 3) sequestering of oxygen atoms near the interface into sites ionically bonded to gallium atoms. These three bonding requirements act synergistically to passivate the interface. The effects are observed in DFT calculations of the local charge densities per atom, interfacial geometry of gallium and arsenic atoms, and local density of states in the band-gap region of the GaAs(001)- @beta@2(2x4) - Ga@sub 2@O interface. These calculations provide a roadmap for identifying passivation oxides for other semiconductor surfaces.