Effect of Structural Phase Transition on Thermally Activated Time-of-Flight Charge Carrier Mobility and Field Effect Tra
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0965-S09-34
Effect of Structural Phase Transition on Thermally Activated Time-of-Flight Charge Carrier Mobility and Field Effect Transport in Diindenoperylene Single Crystals Ashutosh Kumar Tripathi and Jens Pflaum 3rd Institute of Physics, University of Stuttgart, Pfaffenwaldring 57, Stuttgart, 70550, Germany
ABSTRACT We report on the growth, the structural and the electronic characterization of semiconducting diindenoperylene (DIP) single crystals. Temperature dependent X-ray measurements reveal a structural phase transition occurring at around 370 K. Temperature dependent time-of-flight (TOF) hole mobility shows a thermally activated behavior in c’direction up to the phase transition temperature with an activation energy of ~ 180 meV. Complementary, a field effect is successfully demonstrated in the ab-plane on transistors based on DIP single crystal and yields a room temperature hole mobility of about ~ 2×10-5 cm2/Vs. Unlike TOF measurements, no electron transport was observed in field-effect transistors (FETs) geometry which could be attributed to the large injection barrier for electrons at the DIP-Agcontact interface in contrast to the injection barrier for holes. INTRODUCTION Organic electronics has been a field of intense research for the last couple of decades. Sufficiently high charge carrier mobility in the semi-conducting organic layer and a coherent structural order, especially under operation conditions at e.g. elevated temperatures, are prerequisites for the development of high performance electronic devices. Mobility is a tensorial property and does not only dependent on the crystallographic direction but also on the chemical impurities and the structural order of the organic materials [1]. Therefore to achieve an understanding of the microscopic transport mechanisms investigations on high purity and perfectly ordered organic systems, i.e. on ultra-pure organic single crystals, are mandatory. Also, transport of both electrons and holes is desired in order to realize devices like organic ambipolar transistors. In the past, the highest mobilities for electrons and holes have been observed in naphthalene single crystals [2] but this material has a high vapor pressure and hence is unable to form closed highly ordered layers even at room temperature. FETs based on higher linearly condensed polyaromatic hydrocarbons such as tetracene, pentacene and rubrene have been fabricated [3,4,5] but these compounds are very sensitive to oxidation and, therefore, might not be suited to gain insights in the underlying intrinsic mechanisms of electronic transport. In this paper we report on the temperature dependent charge carrier transport in the organic semiconductor DIP along the c’-direction and the effect of the phase transition. Furthermore, we demonstrate field effect transport in the ab-plane for holes in FETs based on single DIP crystals. Thin film transistors of DIP have already been reported to show a mobility strongly increasing with decreasing film texture [6] and advantageously, DIP does not decompose a
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