Evidence of Correlated Mobility Fluctuations in p-Type Organic Thin-Film Transistors

We report on the results of noise measurements in p-type organic thin-film transistors (TFTs) extending from the subthreshold region into the strong accumulation region over four decades of drain current values. The low-frequency noise produced by the devices can be successfully interpreted in the context of a multitrap correlated number fluctuation-mobility fluctuation (CMF) theory, while neither phonon-induced mobility fluctuation nor carrier number fluctuation mechanisms are capable of justifying the observed noise behavior. The Coulomb scattering parameter is found to be in the order of 10⁷ Vs/C, about three orders of magnitude larger with respect to crystalline silicon MOSFETs and comparable with what already reported in hydrogenated amorphous silicon TFTs, suggesting a much more relevant contribution coming from CMF in disordered materials.