On Razors Edge: Influence of the Source Insulator Edge on the Charge Transport of Vertical Organic Field Effect Transist
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On Razors Edge: Influence of the Source Insulator Edge on the Charge Transport of Vertical Organic Field Effect Transistors F. Michael Sawatzki1, Alrun A. Hauke2, Duy Hai Doan3, Peter Formanek4, Daniel Kasemann5, Thomas Koprucki3, and Karl Leo1 1 Dresden Integrated Center for Applied Physics and Photonic Materials IAPP, Dresden, Germany 2 Phillips Universität Marburg, molecular solids, Marburg Germany 3 Weierstraß-Institut für Angewandte Analysis und Stochastik, Berlin, Germany 4 Leibnitz Institut für Polymerforschung, Dresden, Germany 5 CreaPhys GmbH, Dresden, Germany ABSTRACT To benefit from the many advantages of organic semiconductors like flexibility, transparency, and small thickness, electronic devices should be entirely made from organic materials. This means, additionally to organic LEDs, organic solar cells, and organic sensors, we need organic transistors to amplify, process, and control signals and electrical power. The standard lateral organic field effect transistor (OFET) does not offer the necessary performance for many of these applications. One promising candidate for solving this problem is the vertical organic field effect transistor (VOFET). In addition to the altered structure of the electrodes, the VOFET has one additional part compared to the OFET – the source-insulator. However, the influence of the used material, the size, and geometry of this insulator on the behavior of the transistor has not yet been examined. We investigate key-parameters of the VOFET with different source insulator materials and geometries. We also present transmission electron microscopy (TEM) images of the edge area. Additionally, we investigate the charge transport in such devices using driftdiffusion simulations and the concept of a vertical organic light emitting transistor (VOLET). The VOLET is a VOFET with an embedded OLED. It allows the tracking of the local current density by measuring the light intensity distribution. We show that the insulator material and thickness only have a small influence on the performance, while there is a strong impact by the insulator geometry – mainly the overlap of the insulator into the channel. By tuning this overlap, on/off-ratios of 9x105 without contact doping are possible. INTRODUCTION The vertical organic field effect transistor (VOFET) was first introduced by Stutzmann et al. [1] and represents an organic transistor design with much shorter geometric channel length than the lateral OFET. The smaller channel lengths are necessary to provide the high-current and highfrequency needed for electronic applications. This vertical transistor design has been steadily improved over the years ([2], [3]); however, its function and the influence of its components are not understood in the same way as for its lateral counterpart [4]. In addition to its geometric changes, the VOFET contains one additional part in comparison to the lateral OFET – the source insulator. It provides the necessary insulation between the inevitably overlapping source and drain electrodes, to ensure the needed
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