Kohei Terasaki

Current‐Injected Spectrally‐Narrowed Emissions from an Organic Transistor

The spectrally-narrowed emissions (SNEs) such as amplifi ed spontaneous emission are under intense investigation with organic semiconducting materials. [ 1 ] Although various experimental data relevant to SNEs have been accumulated through optically pumping the materials, there have thus far been very few examples of the SNEs attained on an electronic device confi guration. Such examples include the following: Using a light-emitting diode (LED) Liu et al. [ 2 ] observed a narrowed spectral line at 621.7 nm with the full width at half maximum (FWHM) down to 1.95 nm that resulted from a luminescent compound dispersed in a matrix of tris(8-hydroxyquinolinato) aluminum(III) (Alq 3 ). The luminescent layer was sandwiched with a couple of mirrors one of which comprised 7.5 pairs of multilayer dielectric stacks and the other of which consisted of 10 pairs of them. Yokoyama et al. [ 3 ] reported the spectral narrowing that took place on a cleaved device containing a thermally-evaporated luminescent layer sandwiched between the two electrodes of silver and indium tin oxide (ITO). They referred the spectral narrowing to the cutoff mode at the waveguide structure with a silver cladding layer. Thus the SNEs were achieved with great effort on the LED devices with only complicated or elaborated structures. Those efforts are yet away from practical devices. The light-emitting fi eld-effect transistor (LEFET), [ 4 ] in turn, is another candidate for causing the SNE. For the purpose of lessening the threshold power of the lasing, [ 1 ] Gwinner et al. [ 5 ]

Organic Light-Emitting Field-Effect Transistor with Channel Waveguide Structure

Organic field-effect transistors with channel waveguide structures were fabricated with thiophene/phenylene co-oligomer thin films. Top-contact source/drain electrodes of gold were deposited onto both side walls of the waveguide by the self-shadow masking vapor deposition technique leaving the co-oligomer channel of ~5-µm-length intact. The device operated as a typical hole-accumulated unipolar transistor under negative gate biases. When alternating-current gate voltages were applied, the device showed light emission due to recombination of injected electrons with accumulated holes in the waveguide channel.

Superstructures Based upon n- and p-Type Organic Semiconductors: Toward Light-Emitting Device Applications

We have made organic light-emitting field-effect transistors (OLEFETs) using superstructures composed of layered n- and p-type organic semiconductor crystals. The superstructures are fabricated by lamination of the crystals via physical adsorption. The drain and source electrodes made of different kinds of metal are attached to both the upper and lower surfaces of each crystal. Under application of direct-current voltages to the drain and source electrodes, the superstructure OLEFETs emit bright light. The result indicates that the superstructures based on both types of organic crystals are useful for light-emitting devices.