A study of the threshold voltage in pentacene organic field-effect transistors

The threshold voltage and carrier mobilities were characterized in pentacene-based organic field-effect transistors with gold top-contact electrodes for different thickness of the pentacene film. The thickness of the semiconductor layer influences the values of the threshold voltage and, to a lesser extent, the saturation current. In this letter, we show that the thickness-dependent part of the threshold voltage results from the presence of an injection barrier at the gold–pentacene contact. We also show how the ratio between the gate insulator thickness and the semiconductor layer thickness alter the value for the saturation current, and therefore produces values for the field-effect mobility that are too low.