Berlin 2008 – wissenschaftliches Programm

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 3: Organic Devices I

SYSA 3.6: Vortrag

Dienstag, 26. Februar 2008, 16:00–16:15, H 2013

Influence of gap states on the electrical stability of pentacene Thin Film Transistors — •Amare Benor, Arne Hoppe, Veit Wagner, Rahul Dewan, and Dietmar Knipp — Jacobs University Bremen, School of Engineering and Science, 28759 Bremen, Germany

Despite the realization of polycrystalline pentacene transistors with high mobility, the creation of gap states and the influence of gap states on the charge transport and the device stability is still under investigation. In order to study the creation of electronic defects and the influence of these defects on the device stability electrical in-situ measurements of pentacene TFTs were carried out. The TFTs were prepared by Organic Molecular Beam Deposition with hole mobilities ranging from 0.2 − 0.5cm²/Vs. The devices were exposed to oxygen to study the influence on the device characteristics. Unexposed devices are stable, whereas devices exposed to dry oxygen exhibit a shift of the threshold voltage upon prolonged device operation. Stressing the transistor in the on-state (negative bias) leads to a shift of the threshold voltage towards negative gate voltages, whereas prolonged bias stress in the off-state causes a shift of the threshold voltage in the opposite direction. The gap states are formed 0.18 eV (acceptor-like states) and 0.62 eV (donor-like states) above the valence band maxima. The shift of the threshold voltage due to bias stress is determined by the ratio of acceptor-like and donor-like states in the pentacene film. The charge carrier mobility and the on/off ratio of the transistor are not affected by the gap states. A simple density-of-states model will be presented, which allows for the explanation of the experimental results.