AVS 45th International Symposium
    Organic Electronic Materials Topical Conference Monday Sessions
       Session OE+EM-MoA

Paper OE+EM-MoA6
Field Effect Conductance of 1-6 Monolayer Thick Crystals of Organic Semiconductors

Monday, November 2, 1998, 3:40 pm, Room 327

Session: Organic Thin Film Devices II: Transitors and Transport
Presenter: C.D. Frisbie, University of Minnesota
Authors: E.L. Granstrom, University of Minnesota
T.W. Kelley, University of Minnesota
C.D. Frisbie, University of Minnesota
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We describe two types of field effect measurements on organic semiconductor single crystals that are as thin as a single molecular layer. In these studies, crystals of the semiconductors pentacene or sexithiophene are grown by vacuum sublimation onto SiO2, ranging in thickness from 1-6 monolayers with lengths and widths on the order of a micron. In one experiment, individual crystals are contacted with source and drain electrodes fabricated by electron-beam lithography; heavily doped Si underneath the SiO2 serves as a gate electrode. Field effect conductance and carrier mobility are measured as a function of temperature (30-300 K) and the number of discrete molecular layers in the crystals. We find that measurements on these thin crystals are extremely sensitive to carrier trapping and offer a potential approach to dynamic recording of the effects of individual trapping events on source-drain current. A second experiment uses a conducting atomic force microscopy (AFM) probe as a positionable source or drain contact to crystals contacted by a fixed electrode at the other end.@footnote 1@ This configuration allows variation of the source-drain separation and estimation of the organic-metal contact resistance. Resistances associated with defects, e.g., a single grain boundary between adjacent crystals may also be measured. In general, the conjunction of AFM imaging methodology with transport measurements facilitates correlation of transport properties with specific, well-defined organic semiconductor structures. @FootnoteText@ @footnote 1@Loiacono, M. J.; Granstrom, E. L.; Frisbie, C. D. J. Phys. Chem. B 1998, 102, 1679.