Reducing the Barrier Height in Organic Transistors

Reducing the Schottky barrier height and Fermi level de-pinning in metal-organic semiconductor contacts are crucial for enhancing the performance of organic transistors. The reduction of the Schottky barrier height in bottom-contact top-gate organic transistors is demonstrated by adding 1 nm thick atomic layer deposited Al₂O₃ on the source and drain contacts. By using two different donor-acceptor copolymers, both p- and n-type transistors are investigated. Temperature-dependent current–voltage measurements from non-treated, self-assembled monolayer treated, and Al₂O₃ treated Au source-drain contact field-effect transistors with varying channel lengths are carried out. The drain current versus drain voltage near zero gate voltage, which may be described by the thermionic emission model at temperatures above 150 K, allows the estimation of the Schottky barrier height (φ_B). The Al₂O₃ contact-treated transistors show more than 40% lower φ_B compared with the non-treated contacts in the p-type transistor. Similarly, an isoindigo-based transistor, with n-type transport, shows a reduction in φ_B with Al₂O₃ treated contacts suggesting that such ultrathin oxide layers provide a universal method for reducing the barrier height.