Impact of injection limitations on the contact resistance and the carrier mobility of organic field effect transistors

The contact resistance as well as the mobility have developed to key performance indicators for benchmarking organic field-effect transistors. Typically, conventional methods for silicon transistors are employed for their extraction thereby ignoring the peculiarities of organic transistors. This work outlines the required conditions for using conventional extraction techniques for the contact resistance and the mobility based on TCAD simulations and experimental data. Our experimental data contain both staggered and coplanar structures fabricated by exploiting different optimization techniques like SAM treated electrodes, different shearing speeds, PS blending and silicon oxide functionalization. In addition, the work clarifies how injection limited current-voltage characteristics can affect high-performance organic field-effect transistors. Finally, we introduce a semi-physical model for the contact resistance to accurately interpret extracted benchmark parameters by means of the transfer length method (TLM). Guidelines to use conventional extraction techniques with special emphasis on TLM are also provided.