Hall Effect in Organic Single-crystal Field-effect Transistors
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0937-M10-06
Hall Effect in Organic Single-crystal Field-effect Transistors Jun Takeya1,2, Koichi Yamada2, Kazuhito Tsukagoshi3,4, Yoshinobu Aoyagi3,5, Taishi Takenobu6,7, and Yoshihiro Iwasa6,7 1
Chemistry, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka, 560-0043, Japan
2
CRIEPI, Tokyo, 201-8511, Japan
3
RIKEN, Wako, 351-0198, Japan
4
PRESTO, Kawaguchi, 333-0012, Japan
5
Tokyo Institute of Technology, Yokohama, 336-8502, Japan
6
IMR, Tohoku University, Sendai, 980-8577, Japan
7
CREST, Kawaguchi, 333-0012, Japan
ABSTRACT We report Hall effect of charge carriers accumulated in organic field-effect transistors. Rubrene (C42H28) single crystals are shaped for the Hall-bar configuration so that the Hall signal is appropriately detected in external magnetic fields. It turned out that inverse Hall coefficient, having a positive sign, is close to the amount of electric-field induced charge upon the hole accumulation. The observation of the normal Hall effect means that the electromagnetic character of the surface charge is not of hopping carriers but resembles that of a two-dimensional hole-gas system. Moreover, the direct access to the density of mobile charge carriers provides a tool to understand nontrivial features of organic field-effect transistors such as gate electric field dependent mobility. INTRODUCTION As technological progress pushes organic field-effect transistors (OFETs) towards the market, demand for elucidating character of the field-induced charge is getting urgent, desiring a fundamental guide to elevate mobility as well as other device performance factors. Although organic semiconductors have been proven to be available for the elemental circuit components, represented by field-effect transistors (FETs), the full performance of the materials would be significantly reduced in broadly studied polymeric or polycrystalline thin-film devices by extrinsic effects such as those caused by grain boundaries. Recently developed single-crystal OFETs have demonstrated that the FET mobility µFET can be as high as 20 cm2/Vs, and the subthreshold swing is comparable to that of normal single-crystal silicon FETs1-6. The fact that a molecularly flat surface free from dangling bonds is easily grown for the organic single crystals7, may be partially responsible for the superior device parameters. Microscopic transport mechanism, however, is not yet clear of the field-induced charge at the crystalline surface. To find out the intrinsic potentials of these organic materials and to foresee further applications of organic devices, extended study of single-crystal FETs is needed.
Historically, it has been debated for a long time whether poorly doped aromatic organic semiconductors, having the π orbitals of adjacent molecules narrowly overlapped, can realize band transport which justifies the ideal electron-gas picture8. Regarding the Hall effect, the reported results were controversial even for bulk crystals in terms of sign, temperature dependence and the value, possibly because of difficulty in the mea
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