Integration of a Rib Waveguide Distributed Feedback Structure into a Light‐Emitting Polymer Field‐Effect Transistor

• Published in: Advanced functional materials 2009-05, Vol.19 (9), p.1360-1370
• Main Authors: Gwinner, Michael C., Khodabakhsh, Saghar, Song, Myoung Hoon, Schweizer, Heinz, Giessen, Harald, Sirringhaus, Henning
• Format: Article
• Language: English
• Subjects: Distributed feedback; Lasers; Light‐emitting devices; Optoelectronic materials; Organic electronics; Transistors
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200801897

Ambipolar light‐emitting organic field‐effect transistors (LEFETs) possess the ability to efficiently emit light due to charge recombination in the channel. Since the emission can be made to occur far from the metal electrodes, the LEFET structure has been proposed as a potential architecture for electrically pumped organic lasers. Here, a rib waveguide distributed feedback structure consisting of tantalum pentoxide (Ta2O5) integrated within the channel of a top gate/bottom contact LEFET based on poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) is demonstrated. The emitted light is coupled efficiently into the resonant mode of the DFB waveguide when the recombination zone of the LEFET is placed directly above the waveguide ridge. This architecture provides strong mode confinement in two dimensions. Mode simulations are used to optimize the dielectric thickness and gate electrode material. It is shown that electrode absorption losses within the device can be eliminated and that the lasing threshold for optical pumping of the LEFET structure with all electrodes (4.5 µJ cm−2) is as low as that of reference devices without electrodes. These results enable quantitative judgement of the prospects for realizing an electrically pumped organic laser based on ambipolar LEFETs. The proposed device provides a powerful, low‐loss architecture for integrating high‐performance ambipolar organic semiconductor materials into electrically pumped lasing structures. Organic semiconductor lasers: An ambipolar light‐emitting field‐effect transistor based on a polyfluorene (F8BT) is integrated with a rib waveguide distributed feedback structure (see figure) based on Ta2O5. Due to the high refractive index of Ta2O5 the waveguide mode, into which the emitted light couples, is confined sufficiently to eliminate electrode absorption losses. Optical pumping yields low lasing thresholds of 4.5 μJ cm−2.