Conductivity fluctuation within a crystalline domain and its origin in pentacene thin-film transistors

Surface topography and high-resolution potential images in a thin-film transistor with a polycrystalline pentacene active layer have been measured by atomic-force-microscope potentiometry. A potential fluctuation independent of topographic features was found in large flat molecular terraces. The origin of the potential fluctuation was concluded to be the fluctuation of the top level of the highest-occupied-molecular-orbital band, which results in the variation of local carrier concentration. The full width at half maximum of the band fluctuation was estimated to be 12meV, which might reduce the mean carrier velocity in crystalline domains.