Regensburg 2004 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 23: Organische Halbleiter

HL 23.4: Vortrag

Dienstag, 9. März 2004, 17:30–17:45, H13

Field effect in organic MIS structures — •Marcus Ahles, Roland Schmechel, and Heinz von Seggern — Materialwissenschaft, elektronische Materialeigenschaften, TU-Darmstadt, Petersenstra"se 23, 64287 Darmstadt

Organic field effect transistors are attracting more and more attention due to their flexibility and low cost. Charge injection and charge accumulation are basic processes in such devices. To study these processes in more detail, we present the characterisation of the field effect in metal insulator semiconductor (MIS) devices by impedance spectroscopy. The impedance spectra show a strong dependence on the applied bias voltage. Introducing an equivalent circuit and a simple hopping model of charge transport in the organic semiconductor the impedance spectra can be well explained and the centre of the charge distribution in the organic layer can be extracted. Further, charge injection at the semiconductor metal interface is studied. For pentacene we observe both electron and hole accumulation. Unlike holes, which are found close to the insulator interface, electrons are immobilized in the vicinity of the injecting electrode. This is interpreted by the presence of deep electron trap states. The role of those states is further discussed with respect to hysteresis effects in the C-V characteristics as well as in the transistor characteristics. Finally we show, that a gold contact causes an effective p-doping in pentacene. This fact plays an important role in respect to short channel effects in field effect transistors.