Surface and bulk mobilities of oligothiophene single crystals

High-quality single crystals of alpha-quaterthiophene (alpha-4T) and alpha-hexathiophene (alpha-6T) were investigated to compare intrinsic bulk and surface electrical properties. The bulk properties of these organic p-type semiconductors are derived from extended current-voltage characteristics and the surface properties from single crystal field-effect transistor measurements. Most significantly, charge carrier mobilities as high as 0.5 cm(2)/V s are observed in alpha-6T both in the bulk and at the surface. The high quality and purity of the crystals are evident from the low trap densities (<10(15) cm(-3)) and the even lower dopant concentrations (2 x 10(13) for alpha-4T and 7 x 10(10) cm(-3) for alpha-6T). These intrinsically high performance figures, together with the ease of processing, make these oligothiophenes attractive materials for "plastic electronic'' devices. (C) 1998 American Institute of Physics. [S0003-6951(98)02850-2].