Analytic Device Model of Organic Field-Effect Transistors with Doped Channels

Doping has been shown to not only provide additional degrees of freedom in the design of organic field-effect transistors (OFETs) but to increase their performance and stability as well. An analytical model based on the assumption of a square doping profile inside the channel is presented here that describes the effect of doping on the transfer characteristic of OFETs. The model is validated experimentally by a series of OFETs with varying doping conditions. The precise doping profile in the transistor channel is determined by fitting the capacitance/voltage response of doped metal-insulator-semiconductor (MIS) junctions using an AC small-signal drift-diffusion simulation. It is shown that the real doping profile deviates from the simplifying assumptions of the analytical model, i.e., it is found that the effective doping concentration at the dielectric/semiconductor interface is reduced. However, it is shown that the analytical model is not sensitive to this deviation as only the total density charges per unit area determine the changes in the transistor behavior. Overall, the presented theory provides new design rules that can be used to guide the development of doped OFETs with high performance.