Organic field-effect transistors as a test-bed for molecular electronics : a combined study with large-area molecular junctions

The contact resistance of a transistor using self-assembled monolayer (SAM)-modified source and drain electrodes depends on the SAM tunnel resistance, the height of the injection barrier and the morphology at the contact. To disentangle the different contributions, we have combined here the transmission line measurements in transistors with transport measurements of SAMs in large-area molecular junctions. The tunnel resistance of the SAM has been independently extracted in two-terminal large-area molecular junctions. We show that the tunneling resistance of the SAM can be added linearly to the contact resistance of the transistor with bare Au electrodes, to account for the increased contact resistance in the SAM- modified transistor. The observed agreement is discussed. The manifestation of the SAM in the contact resistance shows that transistors can potentially be used as an experimental test-bed for molecular electronics