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Hall Effect of Solution-crystallized and Vapor-deposited 2,7-Dioctylbenzothieno[3,2-b]Benzothiophene Field-effect Transistors


Gate-voltage dependent Hall coefficient R H is measured in high-mobility field-effect transistors of solution-crystallized and vapor-deposited 2,7-dioctylbenzothieno[3,2-b]benzothiophene. The value of R H evolves with density of accumulated charge Q, precisely satisfying the free-electron formula R H = 1/Q near room temperature. The result indicates that the intrinsic charge transport inside the grains is band-like in the high-mobility organic-semiconductor thin films that are of significant interest in industry. At lower temperature, even Hall-effect mobility averaged over the whole polycrystalline film decreases due to the presence of carrier-trapping levels at the grain boundaries, while the free-electron-like transport is preserved in the grains. With the separated description of the inter- and intra-grain charge transport, it is demonstrated that the reduction of mobility with decreasing temperature often shown in organic thin-film transistors does not necessarily mean mere hopping transport.



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1 Izawa, T., Miyazaki, E., and Takimiya, K., Adv. Mater. 20, 3388 (2008).
2 Uemura, T., Hirose, Y., Uno, M., Takimiya, K., and Takeya, J., Appl. Phys. Exp. 2, 111501 (2009).
3 Takeya, J., Kato, J., Hara, K., Yamagishi, M., Hirahara, R., Yamada, K., Nakazawa, Y., Ikehata, S., Tsukagoshi, K., Aoyagi, Y., Takenobu, T., and Iwasa, Y., Phys. Rev.Lett. 98, 196804 (2007).



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