Current-voltage characteristics in organic field-effect transistors. Effect of interface dipoles

- The role of polar species at the semiconductor/insulator interface OFETs is assessed.
- Presence of interface dipoles results in appearance of traps in the semiconductor.
- The depth of dipolar traps decreases with the distance from the interface.
- Spatial inhomogeneity of local mobility affects current-voltage characteristics.

The role of polar molecules present at dielectric/semiconductor interfaces of organic field-effect transistors (OFETs) has been assessed employing the electrostatic model put forward in a recently published paper (Sworakowski et al., 2014). The interface dipoles create dipolar traps in the surface region of the semiconductor, their depths decreasing with the distance from the interface. This feature results in appearance of mobility gradients in the direction perpendicular to the dielectric/semiconductor interface, manifesting themselves in modification of the shapes of current-voltage characteristics. The effect may account for differences in carrier mobilities determined from the same experimental data using methods scanning different ranges of channel thicknesses (e.g., transconductances vs. transfer characteristics), differences between turn-on voltages and threshold voltages, and gate voltage dependence of mobility.