Charge transport in disordered organic field-effect transistors
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Charge transport in disordered organic field-effect transistors Cristina Tanase1, Paul W.M. Blom1, Eduard J. Meijer2, Dago M. de Leeuw3 1 Materials Science Centre and DPI, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands 2 Philips Research Laboratories, Professor Holstlaan 4, 5656 AA Eindhoven, The Netherlands and Delft University of Technology, Department of Applied Physics and DIMES, Lorentzweg 1 2628 CJ Delft, The Netherlands 3 Philips Research Laboratories, Professor Holstlaan 4, 5656 AA Eindhoven, The Netherlands ABSTRACT The transport properties of poly(2,5-thienylene vinylene) (PTV) field-effect transistors (FET) have been investigated as a function of temperature under controlled atmosphere. In a disordered semiconductor as PTV the charge carrier mobility, dominated by hopping between localized states, is dependent on the charge carrier density. The transfer characteristics of PTV FET have been modeled considering the distribution of charge carriers and mobility over the accumulation channel. Good agreement with the experimental data is obtained.
INTRODUCTION In less than one decade a great interest in conjugated polymers has developed, as a result of their potential application in microelectronic devices [1,2]. In order to improve the charge carrier mobility and the on-off current ratio, which are the most important parameters for fieldeffect transistors, the mechanism of charge transport has to be studied. Solution processed thin films made from conjugated polymer have an amorphous or polycrystalline structure and can be characterized as disordered systems. Therefore it can be expected that the transport of carriers within the organic semiconductor is governed by the hopping between localized states [3]. In order to understand the transfer characteristics of disordered organic FET, it is important to realize that the charge carrier density is not uniformly distributed in the accumulation channel, but decreases from the semiconductor/insulator interface into the bulk. In organic FET the mobility is dependent on the charge carrier density, which results from the hopping model. As a consequence the charge carrier mobility does not take a constant value for a certain gate voltage (Vg) like in standard metal-oxide-semiconductor FET, but a distribution of charge carrier mobilities is present in the disordered organic FET. In the present study the electrical characteristics of PTV FET are modeled with a hopping model by taking into account the charge carrier dependence of the mobility in the active channel.
RESULTS AND DISCUSSION Organic field-effect transistors are primarily operating in accumulation mode. A negative voltage applied to the gate of a p-type FET gives rise to band bending in the semiconductor and determines an accumulation of holes into the semiconductor next to the interface [4]. At low drain voltages (the linear regime) the current in the accumulation channel is proportional with the P10.9.1 Downloaded from https://www.cambridge.org/core. Teachers College Library - Col
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