Increase of saturation current in unipolar field-effect transistor due to bulk electric conductance of organic semiconductor

Abstract

We considered an organic field-effect transistor (OFET) based on a squaraine (SQ) fiber, where the electric conductance of the accumulation channel is comparable with the bulk conductance of the SQ fiber. Each of the measured output and transfer current-voltage characteristics was decomposed into two components, representing the conductance of the accumulation channel and the bulk. We present in detail, how the bulk conductance of the fiber can transform the output characteristics of the unipolar OFET. For positive drain and gate voltage, the hole injection from the drain always takes place when a drain voltage is applied. Depending on the ratio between the electron density (ns) injected from the source into accumulation channel and the hole density (pb) injected from the drain into the bulk, the saturation current of the unipolar OFET is constant (pb < ns) or exhibits increase (pb ≥ ns).