Effect of spatial inhomogeneity of charge carrier mobility on current–voltage characteristics in organic field-effect transistors

• A model is presented enabling assessment of effective channel thickness in OFETs.
• The effective channel thickness is a function of the source-drain and gate voltages.
• Spatial inhomogeneity of local mobility affects current–voltage characteristics.
• The model explains voltage-dependent mobilities in spatially inhomogeneous samples.

A semi-quantitative model is put forward elucidating the role of spatial inhomogeneity of charge carrier mobility in organic field-effect transistors. The model, based on electrostatic arguments, allows estimating the effective thickness of the conducting channel and its changes in function of source-drain and gate voltages. Local mobility gradients in the direction perpendicular to the insulator/semiconductor interface translate into voltage dependences of the average carrier mobility in the channel, resulting in positive or negative deviations of current–voltage characteristics from their expected shapes. The proposed effect supplements those described in the literature, i.e., density-dependent mobility of charge carriers, short-channel effects, and contribution of contact resistance.

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