Quasiconductor Model of Transfer Properties of Organic Field‐Effect Transistor

The concept of semiconductor/quasiconductor is applied to reconsider organic field‐effect transistor (OFET) characteristics. Unlike conventional semiconductors (neutral conductors becoming charged insulators under potential application), quasiconductors are neutral insulators that become charged conductors when a space‐charge region forms via carrier injection. They act as voltage‐controlled dielectrics. In OFETs, a quasiconductor layer and dielectric layer are sandwiched between gate (G) and source (S)/drain (D) electrodes. Gate voltage induces a quasiconductor space‐charge layer, forming a conduction channel without inversion. Derived drain current equations, using abrupt distribution and gradual channel approximations, give characteristics similar to metal‐insulator‐semiconductor FETs for back gate top contact (BGTC) and junction FETs for back gate back contact (BGBC) devices. However, at high gate voltages, differential conductance saturates due to accumulation layer saturation, explaining the often‐observed kink in OFET transfer curves. BGBC devices show lower drive currents than BGTC, as their space‐charge region localizes near electrode edges, restricting carrier flow.