Gate tunable electron injection in submicron pentacene transistors

Abstract

We study submicron organic field effect transistors with a pentacene channel, and observe eitherp-type or n-type behaviour under different gate and drain voltage conditions. Transistor structuresof 0.8 µm channel lengths were fabricated by evaporating Au on a tilted substrate, featuring an oxidestep. When evaporating pentacene on the step structure, the edge of the oxide step is usedas a shadow mask to ensure the gap between source and drain. Current–voltagecharacteristics reveal that positive gate voltages increase the drain current, when the lowerAu contact is operated as drain electrode, indicating electron transport through thechannel. When the upper Au contact is used as a drain, the devices display p-typebehaviour. These ambipolar device characteristics are explained in the light of electroninjection enhanced by the submicron geometry, and by electron transport in the presence ofelectron traps.