AVS 47th International Symposium
    Semiconductors Wednesday Sessions
       Session SC+EL+SS-WeM

Paper SC+EL+SS-WeM2
Electrical Transport at Chemically Modified Silicon Surfaces

Wednesday, October 4, 2000, 8:40 am, Room 306

Session: Passivation and Etching of Semiconductors
Presenter: G.P. Lopinski, National Research Council Canada
Authors: O. Hul'ko, National Research Council Canada
R. Boukherroub, National Research Council Canada
C. Mark, National Research Council Canada
S.N. Patitsas, National Research Council Canada
H.Z. Yu, National Research Council Canada
G.P. Lopinski, National Research Council Canada
Correspondent: Click to Email
We are exploring methods for tailoring the electrical conductivity of silicon surfaces via the covalent attachment of atomic and molecular adsorbates. A method for studying the electrical transport properties of wet-chemically modified silicon surfaces has been developed and applied to study of chlorine terminated Si(111). Resistivity measurements (4-probe, van der Pauw geometry) were performed on low doped n-type Si (111) substrates patterned with titanium silicide contacts. These contacts were found to withstand the RCA clean and ammonium flouride etching procedures required to prepare the atomically flat, highly ordered hydrogen terminated Si(111) surfaces that are the starting point for fabricating chemically modified Si(111) surfaces. Chlorine-termination was achieved by UV irradiation of H/Si(111). The resulting surfaces were characterized by STM and Auger, indicating a monolayer of Cl in an ordered (1x1) structure. These Cl/Si(111) surfaces showed a significant (at least one order of magnitude) increase in conductivity with respect to H/Si(111). Under ambient conditions the conductivity decreased exponentially with a time constant of ~1hr., eventually returning to the value measured before chlorination. The enhanced conductivity of the Cl/Si(111) surface is attributed to increased carrier density in the near surface region due to upward band banding caused by the electron withdrawing nature of the adsorbed chlorine. In order to explain the increased conductivity this band bending must be sufficient to cause inversion (>0.6eV). Capacitance measurements indicate that the near surface carrier concentration is increased by at least a factor of 1000 upon chlorination, consistent with the observed conductivity change. Results on other chemically modified surfaces will also be presented.