Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 10: Organic semiconductors
HL 10.4: Vortrag
Montag, 26. März 2007, 15:30–15:45, H14
Temperature Dependence of the Trap State Distribution in C60 Crystals — •A. Ohlinger1, A. Biebersdorf1, R. Dietmüller1, T.A. Klar1, J. Feldmann1, D.V. Talapin2, and H. Weller2 — 1Photonics and Optoelectronics Group, Physics Department and CeNS, Ludwig-Maximilians-Universität München, Germany — 2Institute of Physical Chemistry, University of Hamburg, Germany
Materials comprising C60 are of great interest and are used in optoelectronic devices such as FETs, photoconductors or photovoltaic devices. Charge transport in C60 crystals is dominated by trap states. The density of these trap states is commonly assumed to decay exponentially with the energetic depth from the conductivity edge.
In this contribution, we quantitatively determine the parameters of the trap state distribution by photodoping C60 microcrystals. We find the characteristic trap depth to decrease by nearly 40% during the phase transition of the C60 crystals from the fcc to the sc phase between 250 K and 200 K and the activation energy drops by approximately 50%. The conductivity below 200 K is predominately governed by trap states which are introduced by oxygen. In contrast, at room temperature trap states are dominantly related to the rotation of the C60 molecules. Calculations based on our data show that the number of trap states at room temperature is about 100 times larger than below 200 K.
For the future we expect that photodoping will be used to determine characteristic parameters of trap states in other amorphous organic or inorganic semiconductors, as well.