Light usually diffracts in all directions when it emerges from a subwavelength aperture, which puts a lower limit on the size of features that can be used in photonics. This limitation can be overcome by creating a periodic texture on the exit side of a single aperture in a metal film. The transmitted light emerges from the aperture as a beam with a small angular divergence (approximately ±3°) whose directionality can be controlled. This finding is especially surprising, considering that the radiating region is mainly confined to an area with lateral dimensions comparable to the wavelength of the light. The device occupies no more than one cubic micrometer and, when combined with enhanced transmission, suggests that a wide range of photonic applications is possible.

https://science.sciencemag.org/content/sci/early/2002/06/20/science.1071895.full.pdf

Beaming light from a subwavelength aperture.

Since 1993, InGaN light-emitting diodes (LEDs) have been improved and commercialized, but these devices have not fulfilled their original promise as solid-state replacements for light bulbs as their light-emission efficiencies have been limited. Here we describe a method to enhance this efficiency through the energy transfer between quantum wells (QWs) and surface plasmons (SPs). SPs can increase the density of states and the spontaneous emission rate in the semiconductor, and lead to the enhancement of light emission by SP–QW coupling. Large enhancements of the internal quantum efficiencies (etaint) were measured when silver or aluminium layers were deposited 10 nm above an InGaN light-emitting layer, whereas no such enhancements were obtained from gold-coated samples. Our results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.

/pdf/surface-plasmon-enhanced-light-emitters-based-on-ingan-4ithz2fei5.pdf

Surface-Plasmon-Enhanced Light Emitters Based on InGaN Quantum Wells

Over the past decade, advances in LEDs have enabled the potential for wide-scale replacement of traditional lighting with solid-state light sources. If LED performance targets are realized, solid-state lighting will provide significant energy savings, important environmental benefits, and dramatically new ways to utilize and control light. In this paper, we review LED performance targets that are needed to achieve these benefits and highlight some of the remaining technical challenges. We describe recent advances in LED materials and novel device concepts that show promise for realizing the full potential of LED-based white lighting.

LEDs for Solid-State Lighting: Performance Challenges and Recent Advances

Surface plasmons (SPs) have attracted much attentions because optical properties can be greatly enhanced by coupling between SPs and the multiple quantum wells(MQWs) in light-emitting diodes(LEDs). We demonstrate the SP enhanced InGaN/GaN MQW blue LED with an Ag nanoparticle layer located underneath the MQWs. An enhancement of 32.2% of optical output power of the LED was observed at an input current of 100 mA. The time resolvedphotoluminescence(PL) result showed that the PL decay time of the LED with Ag nanoparticles was significantly decreased compared to that of the LED without Ag nanoparticles, indicating that the spontaneous emission rate was increased by the energy transfer between the QW light emitter and the SP of Ag nanoparticle. This result shows that the Ag nanoparticles can be used to greatly increase the internal quantum efficiency of InGaN/GaN MQW blue LED through the coupling of excitons in MQWs and SPs in Ag nanoparticles.

/pdf/surface-plasmon-enhanced-light-emitting-diodes-1i29rugjke.pdf

Surface-Plasmon-Enhanced Light-Emitting Diodes†

This invention describes new LEDs having light extraction structures (26) on or within the LED to increase its efficiency. The new light extraction structures (26) provide surfaces for reflecting, refracting or scattering light into directions that are more favorable for the light to escape into the package. The structures can be arrays of light extraction elements (42, 44, 46, 48, 50, 52) or disperser layers (112, 122, 134, 144, 152, 162). The light extraction elements can have many different shapes and are placed in many locations to increase the efficiency of the LED over conventional LEDs. The disperser layers provide scattering centers for light and can be placed in many locations as well. The new LEDs with arrays of light extraction elements are fabricated with standard processing techniques making them highly manufacturable at costs similar to standard LEDs. The new LEDs with disperser layers are manufactured using new methods and are also highly manufacturable.

Enhanced light extraction in LEDs through the use of internal and external optical elements

We show for the first time that strongly directional emission of defined polarization can be achieved from conventional AlGaAs/GaAs double heterostructure surface emitting LEDs via coupling to surface plasmons. By microstructuring the surface, we have fabricated LEDs with a beam divergence of less than 40 and a drastically increased quantum efficiency. We prove that surface plasmon excitation aid emission mechanism has the potential to overcome basic external quantum efficiency losses and to improve the performance of LEDs.

M. Hauser

Papers

Strongly directional emission from AlGaAs/GaAs light emitting diodes