Ambipolar injection in a submicron-channel light-emitting tetracene transistor with distinct source and drain contacts

We report on organic light-emitting transistors with a submicron-channel length, gold source, and calcium drain contacts. The respective contact metals allow efficient injection of holes and electrons in the tetracene channel material. Transistor characteristics were measured in parallel with electroluminescence being recorded by a digital camera focused on the transistor channel. In the case of submicron-channel lengths, the transistor source-drain current at higher gate voltages was determined by the source-drain voltage. At larger channel lengths, the source-drain current was limited by the injection of electrons from the calcium contact, as hole ejection to this contact was fully blocked. The hole blocking is explained in terms of a chemical reaction occurring at the Ca/tetracene interface.