Electrical response of highly ordered organic thin film metal-insulator-semiconductor devices

We report a detailed investigation of the electrical properties of organic field-effect transistors (OFETs) and metal-insulator-semiconductor (MIS) capacitors formed from highly ordered thin films of C60 as the active semiconductor and divinyltetramethyl disiloxane-bis(benzocyclobutene) (BCB) as the gate dielectric. Current-voltage measurements show the OFETs to be n-channel devices characterized by a high electron mobility (∼6 cm2/V s). An equivalent circuit model is developed which describes well both the frequency and voltage dependences of the small-signal admittance data obtained from the corresponding MIS capacitors. By fitting the circuit response to experimental data, we deduce that increasing gate voltages increases the injection of extrinsic charge carriers (electrons) into the C60. Simultaneously, the insulation resistance of the BCB decreases, presumably by electron injection into the insulator. Furthermore, the admittance spectra suggest that the capacitance-voltage (C-V) behavior originates from a parasitic, lateral conduction effect occurring at the perimeter of the capacitor, rather than from the formation of a conventional depletion region.