Crystallite size effect on the hole mobility of uniaxially aligned copper phthalocyanine thin-film field-effect transistors

We fabricated copper plithalocyanine (CuPc) thin-film field-effect transistors (FETs) with three different orientations of CuPc with respect to channels. The substrate rubbing treatment induced uniaxial orientation in CuPc layers, yielding higher hole mobility (similar to0.02 cm(2)/V S) than that of untreated FETs. Although the rubbing treatment bore high-aspect-ratio (> 10) CuPc domains oriented to rubbing direction, the mobility anisotropy of the film was only 1.4. This discrepancy was explained by analyzing grazing-incidence x-ray diffraction profiles, i.e.: (1) In-plane mean size of crystals was smaller than their appearance in atomic force microscopy, and (2) the crystallites were much shorter in the apparent long-hand direction (I I nm) than the direction perpendicular to it (44 nm). (C) 2005 American Institute of Physics.