Impact of Gate Voltage on Mobility of Charge Carriers in Conductive Channel of Organic Molecular Semiconductors: Transport Landscape Assessed by Alternating and Direct Current Mode Techniques

Abstract

AbstractThe gate voltage dependence of the charge carrier mobility is investigated by the microwave resonance technique in transport channels at various organic semiconductors‐insulator interfaces. Although the microwave based measurement is free from the Schottky‐barrier, the vertical charge transport, and the minority carrier trapping, which have been regarded as the origin of the nonlinearity in field effect transistor (FET) measurements, the obtained charge carrier mobility is impacted significantly by the applied gate bias. Atomic force microscopy (AFM) and X‐ray diffractometry (XRD) measurements revealed that the observed nonlinearity indeed originates from the surface disorder in even polycrystalline materials including conjugated polymers. The concerted assessment of the microwave resonance and the FET measurements reveals that 1) injected carriers below the threshold voltage are not trapped despite of the absence of the drain current, 2) the only charge carrier mobility at the 1st layer is assessed by FET measurements, and 3) the threshold voltage of conjugated polymers is relatively low due to the intra‐domain connection through tie molecules.