Regensburg 2007 – scientific programme
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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices
SYOE 8: Poster Session SYOE
SYOE 8.83: Poster
Tuesday, March 27, 2007, 18:00–20:00, Poster B
Current Transport Mechanism in a Pentacene Diode with a Tunneling Contact revealed by Numerical Simulation — •Thomas Lindner1, Gernot Paasch1, Christof Wöll2, Lars Ruppel2, Alexander Birkner2, Gregor Witte2, and Carsten Busse2 — 1IFW Dresden, Germany — 2Ruhr-Universität Bochum
A diode-like device has been fabricated [1] by deposition of pentacene on a surface-modified, single-crystalline Au-substrate. The tip of an STM is used as a tunneling electrode. The current-voltage characteristics of this device reveal an asymmetry with respect to the polarity, depending on film thickness [1]. Numerical simulations allow to relate the onset of the current at positive sample bias (depending on pentacene film thickness) to n-conduction, in contrast to the commonly observed p-type for poly-crystalline pentacene. The origin of this peculiarity is that for low positive voltage the hole current injected from the substrate limits the electron tunneling from the tip to the pentacene layer. This small hole current results in an increasing voltage drop between tip and layer. Once this voltage drop compensates the electron barrier, direct tunneling of electrons into the pentacene LUMO leads to a steeply increasing electron current, which shifts with the pentacene layer thickness. In contrast, at negative sample bias direct tunneling of electrons into the LUMO does not occur. A steeply increasing hole current is observed that is independent on pentacene film thickness.
[1] L. Ruppel, A. Birkner, G. Witte, C. Busse, T. Lindner, G. Paasch, Ch. Wöll, submitted.