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1091-AA10-03

In-crystal Carrier Transport in Organic Single Crystal Transistors J. Takeya1, M. Yamagishi1, Y. Tominari1, Y. Iwasaki1, and M. Uno2 1

Osaka University, Toyonaka, 560-0043, Japan

2

TRI-Osaka, Izumi, 594-1157, Japan

ABSTRACT We report a series of our experiments using organic single crystals to reach the maximum performance intrinsic to the materials. A consequence of the experiments is that a prescription for realizing high-mobility devices is to induce carriers in inner crystals to avoid scattering at the surfaces. Intrinsic-semiconductor character of the high-purity organic crystals favors thermal diffusion of the carriers into the crystals in the presence of weak gate-electric fields. Furthermore, it is demonstrated that the high-mobility transport of the in-crystal carriers are highlighted in double-gate single-crystal transistors with the two gate electric field balanced with each other.

INTRODUCTION Developing high-mobility organic field-effect transistors (OFETs) is one of the key technologies that can extend a market of organic electronics, providing easy-to-fabricate switching components in fundamental logic circuits, for example [1-3]. Though it is mostly argued that the electric-field induced carriers reside at the surface of organic semiconductors next to the gate insulating layers, the higher carrier mobility should be obtained if organic semiconductor crystals are used and the carriers are located deeper in the crystals, where organic molecules are literally a. In this presentation, we report a series of our experiments using organic single crystals to reach the maximum performance intrinsic to the materials. Our experiments features development of the organic single-crystal devices[4], achievement of the bench-mark mobility of 30-40 cm2/Vs [2], establishment of Hall-effect measurement to directly estimate density of the electric-field induced carriers [1,5], and the structure of the double-gate single-crystal transistor to study transport properties of carriers distributed inside the crystal [3]. From

the above experiments, it turned out that intrinsic-semiconductor character of high-purity organic crystal semiconductor favors thermal diffusion of the carriers into the crystals in the presence of weak gate-electric fields.

EXPERIMENTAL Crystal growth The rubrene single crystals used for active layers were grown by physical vapor transport. Commercial sublimed grade product of Aldrich 551112 were vaporized and crystallized. The resultant crystals were brought to the sublimation boat and were recrystallized, so that purer rubrene crystals can be grown. 9,10-diphenylanthracene (DPA) crystals, used for organic gate insulator crystals, were also grown by the same technique. Device fabrication Picking up a thin crystal with the thickness of less than 1 µm, we attached it electrostatically to various gate insulators on which gold electrodes for each experiment were patterned with photolithography technique. An advantage of the technique is full variation of gate insulating layers and of