AVS 45th International Symposium
    Electronic Materials and Processing Division Thursday Sessions
       Session EM-ThM

Paper EM-ThM7
Effect of Surface Interactions on Band Offsets at Buried Semiconductor-Insulator Interfaces

Thursday, November 5, 1998, 10:20 am, Room 316

Session: Compound Semiconductor Surface Chemistry
Presenter: B.R. Schroeder, University of Washington
Authors: B.R. Schroeder, University of Washington
S. Meng, University of Washington
M.A. Leskovar, University of Washington
M.A. Olmstead, University of Washington
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Once an interface between two materials is buried, it is generally assumed to be stable. However, when a CaF@sub 2@/Si film is exposed to atmosphere, the interface spacing increases by 1.7 Å and the band offset decreases by 0.5 eV. The mechanism for this modification of a buried interface is not understood. We have investigated the effect of surface exposure on the band offset at a buried CaF@sub 2@/Si(111) interface. Thin films (4-6 monolayers) of CaF@sub 2@, grown by molecular beam epitaxy on Si(111) substrates, were exposed to atmospheric pressure of various atmospheric constituents and the change in band offset was measured by core level photoemission spectroscopy. Exposure to nitrogen had a negligible effect, while exposure to water vapour (+ nitrogen) had the same result as atmosphere. Exposure to oxygen also reduced the band offset, but by a smaller amount. The decrease in band offset was partially reversible upon annealing at 450 °C. Besides the decrease in band offset, exposure to water or atmosphere also leads to the disappearance of the interface photoemission satellite. This may indicate a structural change in bonding at the interface, which in turn would alter the interface dipole. The magnitude of the band offset and decay of the interface satellite scale roughly with the amount of oxygen present in the film. To test this correlation, silicon was deposited at room temperature on (unexposed) CaF@sub 2@/Si(111). The band offset at the lower interface again decreased by about 0.5 eV, but in this case no additional oxygen was observed. This indicates that oxygen is sufficient to change the band offset but not necessary.