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Dresden 2009 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 44: Organic semiconductors I

HL 44.2: Talk

Thursday, March 26, 2009, 11:00–11:15, POT 51

In-situ study of electronical properties of pentacene transistors during growth — •Daniel Beckmeier1,2, Matthias Fiebig1, and Bert Nickel11Department für Physik, Ludwig-Maximilians-Universität, D-80539 München — 2Institut für Physik, Universität der Bundeswehr München, D-85579 Neubiberg

Organic thin film transistors (TFT) with pentacene as semiconductor material were grown by molecular beam deposition (MBD). They were electrically characterized in situ during growth at vacuum conditions to analyze the dependence of the electronic properties on the film thickness of the pentacene layer.

TFT structures were electrically connected inside the MBD chamber. The channel length of the structures was 25 μm. A 150 nm thick silicon oxide was used as gate dielectric. To improve the pentacene film growth, polymer layers (polystyrene and cyclic olefin copolymer) were spin-coated on top of the oxide. Pentacene was evaporated onto the structures. Simultaneously, the transfer and output characteristics were measured. The data was analyzed using TFT theory to extract the mobility and threshold voltage as a function of film thickness. Starting from about 1 nm film thickness, a linear increase of mobility with film thickness was observed. The mobility saturated at film thicknesses between 8 and 30 nm, depending on substrate and growth conditions. Once transferred to ambient conditions, the TFTs showed a strong hysteresis, a reduction in mobility and a shift of the threshold voltage towards more positively biased values.

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