Light-induced switching in back-gated organic transistors with built-in conduction channel

We report an observation of light-induced switching of conductance in back-gated organic field-effect transistors (OFETs) with a built-in conduction channel. In the studied devices, the built-in channel is formed owing to the self-sensitized photo-oxidation of the rubrene surface. In the dark, the back gate controls charge injection from metal contacts into the built-in channel: The high-current ON state corresponds to zero or negative back gate voltage; the low-current OFF state-to a positive back gate voltage that blocks the Schottky contacts. Illumination of an OFET in the OFF state with a short pulse of light switches the device to the ON state, which persists in the dark for days. The OFF state can be restored by cycling the back-gate voltage. The observed effect can be explained by screening the back-gate electric field with the charges photogenerated in the bulk of organic semiconductor. (C) 2004 American Institute of Physics.