Charge transport in oligothiophene field-effect transistors

Temperature-and electric-field-dependent mobility measurements of polycrystalline alpha-sexithiophene thin films, which form the active layer in field-effect transistors, are reported and are found to be strongly sample dependent. In samples with significant charge trapping, the mobility at temperatures greater than 50 K occurs by thermally activated hopping. There is a correlation between the extent of charge trapping and the magnitude of the field-effect mobility. In most samples, the field-effect mobility at temperatures less than 40 K is approximately temperature independent, but with an absolute value that is sample dependent. If the effects of trapping are neglected, the mobility in these field effect transistors possesses two main components: a nearly temperature-independent component and a temperature activated component.