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High-brightness polarized light-emitting diodes

2012; Springer Nature; Volume: 1; Issue: 8 Linguagem: Inglês

10.1038/lsa.2012.22

2095-5545

Elison Matioli, Stuart Brinkley, Kathryn M. Kelchner, Yan-Ling Hu, Shuji Nakamura, Steven P. DenBaars, James S. Speck, Claude Weisbuch,

Semiconductor Quantum Structures and Devices

Light-emitting diodes are becoming the alternative for future general lighting applications, with huge energy savings compared to conventional light sources owing to their high efficiency and reliability. Polarized light sources would largely enhance the efficiency in a number of applications, such as in liquid-crystal displays, and also greatly improve contrast in general illumination due to the reduction in indirect glare. Here, we demonstrate light-emitting diodes presenting high-brightness polarized light emission by combining the polarization-preserving and directional extraction properties of embedded photonic-crystals applied to non-polar gallium nitride. A directional enhancement of up to 1.8-fold was observed in the total polarized light emission together with a high polarization degree of 88.7% at 465 nm. We discuss the mechanisms of polarized light emission in non-polar gallium nitride and the photonic-crystal design rules to further increase the light-emitting diode brightness. This work could open the way to polarized white-light emitters through their association with polarization-preserving down-converting phosphors. Researchers have designed a light-emitting diode (LED) that produces bright directional polarized blue light. The device, developed at the University of California at Santa Barbara in the USA by Elison Matioli and collaborators, is based on a variant of the semiconductor gallium nitride, grown on a specifically crystal direction that yields emission of polarized light. The researchers improved light extraction from the device by drilling aligned arrays of holes at precisely defined intervals into the substrate. This photonic crystal structure selectively enhances the emission of polarized light for particular emission angles by up to a factor of 1.8. High-brightness LEDs emitting polarized light are of interest for flat-screen displays, and also for household lighting because they minimize the glare from light reflections.