Development of Organic Semiconductor Lasers with Self-organized Low-dimensional Crystals of π-Conjugated Oligomers

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This study was carried out to realize organic semiconductor lasers using self-organized low-dimensional crystals of π-conjugated oligomers based on their confinement effects of excitons and light. The results are summarized as follows.(1) Development of laser dye moleculesWe found that π-conjugated linear oligomers of distyrylbenzene derivatives, thiophene and p-phenylene are promising as stable lasing materials with good emission efficiency under high current injection.(2) Fabrication of self-organized low-dimensional crystalsThe self-organized low-dimensional crystals were successfully prepared by vapor-deposition of the above oligomers onto the (100) surface of a KCl single-crystal substrate. The oligomer of the distyrylbenzene derivative was self-olganized in dotlike morphology of 1-10 μm in diameter. The tiophene/phenylene co-oligomers grew in epitaxially oriented rodlike crystals.(3) Optically pumped light amplification phenomena of self-organized low-dimensional crystalsThe self … More -organized microdots and epitaxially oriented rodlike crystals were optically pumped by a pulsed excition laser and their photoluminescence spectra were observed. The emitted light was confined in these low-dimensional crystals and gain-narrowed by their microcavity and self-waveguiding effects resulting in the amplified spontaneous emisson (ASE) with a band width of several nanometers. Furthermore,by changing the excitation wavelengths, unusually narrowed emission (band width < 0.5 nm) related to the Raman scattering process was obtained. It was assigned as the stimulated resonance Raman scattering that was indicative of polaritonic interaction between the emitted light and the excitons localized at a specific molecular vibration mode.(4) Current injection characteristics of FET devices fabricated with self-organized low-dimensional crystalsCarrier injection and transport properties of field effect transistors fabricated with the self-organized low-dimensional crystals were measured. The highest hole mobility, 0.015 cm2V-1s-1, was obtained from the epitaxially oriented crystals of the thiophene/phenylene co-oligomer. It suggests that the crystal orientation with respect to the channel direction is important to improve the carrier transport efficiency. Less