Gated nonlinear transport in organic polymer field effect transistors

TL;DR

This study investigates hole transport in organic polymer transistors across various temperatures and channel lengths, revealing a transition to nonlinear, Poole-Frenkel-like hopping conduction at low temperatures.

Contribution

It provides the first detailed analysis of nonlinear transport mechanisms in polymer transistors, demonstrating a bulk-limited conduction and a crossover in hopping behavior at low temperatures.

Findings

Transport is bulk-limited at room temperature.

Nonlinear conduction fits a Poole-Frenkel-like hopping model.

Crossover from thermally activated to nonthermal hopping below 30 K.

Abstract

We measure hole transport in poly(3-hexylthiophene) field effect transistors with channel lengths from 3 $\mu$m down to 200 nm, from room temperature down to 10 K. Near room temperature effective mobilities inferred from linear regime transconductance are strongly dependent on temperature, gate voltage, and source-drain voltage. As $T$ is reduced below 200 K and at high source-drain bias, we find transport becomes highly nonlinear and is very strongly modulated by the gate. We consider whether this nonlinear transport is contact limited or a bulk process by examining the length dependence of linear conduction to extract contact and channel contributions to the source-drain resistance. The results indicate that these devices are bulk-limited at room temperature, and remain so as the temperature is lowered. The nonlinear conduction is consistent with a model of Poole-Frenkel-like hopping mechanism in the space-charge limited current regime. Further analysis within this model reveals consistency with a strongly energy dependent density of (localized) valence band states, and a crossover from thermally activated to nonthermal hopping below 30 K.