Mobility overestimation due to gated contacts in organic field-effect transistors
Emily G. Bittle, David J. Gundlach, Oana Jurchescu, James I. Basham, Thomas Jackson
Parameters used to describe the electrical properties of organic field-effect transistors, such as mobility and threshold voltage, are commonly extracted from measured currentvoltage characteristics and interpreted by using the classical metal oxidesemiconductor field-effect transistor model. However, in recent reports of devices with ultra-high mobility (>40 cm2 V−1 s−1), the device characteristics deviate from this idealized model and show an abrupt turn-on in the drain current when measured as a function of gate voltage. In order to investigate this phenomenon, here we report on single crystal rubrene transistors intentionally fabricated to exhibit an abrupt turn-on. We disentangle the channel properties from the contact resistance by using impedance spectroscopy and show that the current in such devices is governed by a gate bias dependence of the contact resistance. As a result, extracted mobility values from d.c. currentvoltage characterization are overestimated by one order of magnitude or more.