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We report on electrically driven amplified spontaneous emission and lasing in tetracene single crystals using field-effect electrodes for efficient electron and hole injection. For laser action, feedback is provided by reflections at the cleaved edges of the crystal resulting in a Fabry-Perot resonator. Increasing the injected current density above a certain threshold value results in the decreasing of the spectral width of the emission from 120 millielectron volts to less than 1 millielectron volt because of gain narrowing and eventually laser action. High electron and hole mobilities as well as balanced charge carrier injection lead to improved exciton generation in these gate-controlled devices. Moreover, the effect of charge-induced absorption is substantially reduced in high-quality single crystals compared with amorphous organic materials.
Semiconductor lasers are widely used in modem science and technology. Compared with conventional inorganic semiconductors, organic semiconductors offer potential advantages with respect to easy processing, lower cost, and flexibility. Hence, electrically driven lasers based on organic semiconductors might find a wide range of applications. Optically excited lasing and amplified spontaneous emission have been observed in a wide range of semiconducting polymers, small molecules, and organic single crystals (1-9). Moreover, amorphous or nearly amorphous organic and polymeric semiconductors have been very successfully used in thin-film organic light-emitting devices (OLEDs). These devices typically require injection current densities of 1 to 10 mA/ cm^sup 2^ to achieve brightnesses of order 100 cd/m^sup 2^ (4). For laser applications, substantially higher current densities will be required. Reduced luminescence efficiencies at high injection current densities and charge-induced absorption have been identified as major problems for electrically pumped OLEDs (4, 10, 11). Another limiting factor is the low charge carrier mobility. As an electrically driven device is strongly influenced by the transport properties of the semiconductor, we focus on organic materials that exhibit high mobilities for electrons as well as holes.
Materials properties. Mobilities on the order of 2 cm^sup 2^ V^sup -1^ s^sup -1^ can be achieved in tetracene at room temperature. This is more than four orders of magnitude higher than mobilities in materials used in conventional OLEDs (4, 8, 10). Tetracene also offers a reasonably high photoluminescence quantum yield, and electroluminescence has been reported for single-crystal diodes (12). Optically pumped amplified spontaneous emission has been observed in...