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Use of doping to achieve low contact resistance in bottom-gate top-contact type organic transistor with liquid-crystalline organic semiconductor, Ph-BTBT-10

We have investigated the characteristics of bottom-gate and top-contact type field effect transistors fabricated with polycrystalline thin films of a liquid-crystalline organic semiconductor, 2-decyl-7-phenyl-benzothienobenzothiophene (Ph-BTBT-10), with a p-type dopant, tetrafluoro-tetracyano-quinodimethane (F4-TCNQ). We found that the contact resistance between the semiconductor and electrode was reduced from 3.0 kΩ cm to 1.2 kΩ cm by contact doping with F4-TCNQ, and to 0.9 kΩcm by subsequent thermal annealing of the films, in which the F4-TCNQ dopant diffused from the surface to the interior of the Ph-BTBT-10 thin film. In addition, we found that contact-doped and thermally annealed devices showed higher mobility and smaller threshold voltage in short-channel devices compared to pristine devices. We conclude that thermal diffusion of dopants to improve FET performance is an important technique.