Considerable attention has recently been paid to light-emitting organic filed-effect transistors (LEOFETs) because of their potential applications to novel opto-electronic devices. In most LEOFETs, light emission occurs through the recombination of carriers injected from electrodes. Various efforts have been, thus, made to improve injection and transport properties of minority carriers in organic materials. On the other hand, light emission was frequently observed when we applied reverse bias voltages, that is, positive bias voltages, to the drain electrode for p-type FETs with grounded source and negatively biased gate electrodes. In this circuit, minority carriers were not injected into organic semiconductors. Nevertheless, the luminous intensity increased with drain voltage.
In the present work, we have prepared such novel type LEOFETs with various device structures. We have inserted thin metal wires between the source and drain electrodes in the channel region of pentacene FETs. It was found that the light emission was observed around the metal wires inserted and the luminous efficiency was improved with the number of wires. The luminescence spectrum was identical to that of pentacene films. The light emission was thought to be generated by via energy transfer to the pentacene films from plasmon excited on metal surfaces by current injection.