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ABSTRACT: We report the observation of room temperature lasing action in optically pumped GaN nanopillars. The nanopillars were fabricated by patterned etching and crystalline regrowth from a GaN substrate. When nanopillars were optically excited, a narrow emission peak emerged from the broad spontaneous emission background. The increasing rate is nine times faster than that of the spontaneous emission background, showing the onset of lasing action. The lasing occurs right at the center of spontaneous emission rather than the often reported redshifted wavelength. A spectroscopic ellipsometry analysis indicates that the gain of lasing action is provided by exciton transition.
Optics Express 09/2011; 19(19):17960-5. · 3.59 Impact Factor
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ABSTRACT: High efficiency white light-emitting diodes with superior color-mixing have been investigated. It is suggested that the patterned remote phosphor structure could improve the uniformity of angular-dependent correlated color temperature (CCT) and achieve high chromatic stability in wider operating current range, as compared to the conventional remote phosphor coating structure. In this experiment, we employed a pulse spray coating method to place the patterned phosphor on the package and to leave a window region. The window area, a clear space without coating of the phosphor not only increases the extraction efficiency of blue rays at large angle, but also improves the stability of angular-dependent CCT. Moreover, the CCT deviation could be reduced from 1320 K to 266 K by this patterned remote phosphor method, and the stray blue/yellow light within the package can be effectively reduced and controlled. The design was verified both experimentally and theoretically.
Optics Express 07/2011; 19 Suppl 4:A930-6. · 3.59 Impact Factor
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ABSTRACT: We demonstrate the output power enhancement of ultraviolet light-emitting diodes (UVLEDs) by epitaxial lateral over growth (ELOG) on a distributed Bragg reflector (DBR) patterned substrate. The patterned DBR mesas are used as ELOG masks to improve material quality as well as reflectors to enhance the light output coupling. Compared with the conventional UVLEDs, the surface pit density of UVLEDs at regions right above embedded patterned DBR were reduced from 2.5 × 10<sup>6</sup> to 1.6 × 10<sup>6</sup> cm<sup>-2</sup>. The improved light extraction efficiency is verified by ray tracing simulation. The luminous intensity of this novel structure is enhanced by 75% compared to that of reference UVLED structure at the wavelength 390 nm.
IEEE Photonics Technology Letters 06/2011; · 2.19 Impact Factor
