Insight into the contact resistance problem by direct probing of the potential drop in organic field-effect transistors

The microscopic electric field induced second-harmonic generation technique is used for direct observation of electric field profiles and evaluation of the potential drop on the injection electrode in the organic field-effect transistors with various channel lengths L. It is found that the potential drop on injection electrode is not a function of L. We show that the analysis of the transmission line model (TLM) cannot distinguish channel length independent contact resistance and potential drop. Tracing back to the conceptional idea of contact resistance proposed by Shockley in 1964, the TLM approach is discussed to explain L-dependent contact resistance.