Trapping in organic field-effect transistors

Current-voltage characteristics of single- and polycrystalline organic fiel d-effect transistors are analyzed. The effect of bulk, interface, and grain boundary traps is investigated. The frequently observed dependence of the field-effect mobility on the gate voltage is ascribed to trapping processes rather than to an intrinsic charge transport mechanism in these organic se miconductors. Furthermore, the thermally activated mobility in polycrystall ine devices, frequently observed, is ascribed to the formation of a potenti al barrier at the grain boundaries of the polycrystalline semiconductor. Th e barrier height depends significantly on the trap density and the position of the Fermi energy and therefore on the gate voltage. (C) 2001 American I nstitute of Physics.