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

Fluorescence is widely used in optical devices, microscopy imaging, biology, medical research and diagnosis. Improving fluorescence sensitivity, all the way to the limit of single-molecular detection needed in many applications, remains a great challenge. The technique of surface enhanced fluorescence (SEF) is based upon the design of surfaces in the vicinity of the emitter. SEF yields an overall improvement in the fluorescence detection efficiency through modification and control of the local electromagnetic environment of the emitter. Near-field coupling between the emitter and surface modes plays a crucial role in SEF. In particular, plasmonic surfaces with localized and propagating surface plasmons are efficient SEF substrates. Recent progress in tailoring surfaces at the nanometre scale extends greatly the realm of SEF applications. This review focuses on the recent advances in the different mechanisms involved in SEF, in each case highlighting the most relevant applications.

http://turroserver.chem.columbia.edu/surfaceplasmons/pdf/53_jpd_41_1_2008_sefsrev.pdf

Surface enhanced fluorescence

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†

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.

Strongly directional emission from AlGaAs/GaAs light emitting diodes

A polarization detector based on the excitation of surface plasmon polaritons on the periodically corrugated metal surface of Schottky structures is presented. The surface modes are only excited by light having the appropriate polarization; they are leaky at the metal-semiconductor interface and are thus radiated into the semiconductor, where they generate charge carriers. By this mechanism the photocurrent of the device is enhanced and depends strongly on the polarization angle of the incident light. By use of two detectors with different grating orientations the polarization of the light can be determined unambiguously.

Polarization-sensitive surface plasmon Schottky detectors.

We have investigated the light emission from forward‐ and reverse‐biased sinusoidally structured Ag/n‐GaAs Schottky diodes. Sinusoidally structured Schottky junctions show increased light emission because of the radiative decay of excited surface plasmon polaritons, resulting in drastically enhanced quantum efficiency. A model explaining excitation and emission of surface plasmon polaritons is presented.

Surface plasmon polariton enhanced light emission from Schottky diodes

Narrowband photosignals with quantum efficiencies up to 30% are observed on Al‐SiO2‐p‐Si junctions. The frequency selective photosignals are due to surface plasmon polaritons confined to the metal‐air interface excited by grating coupling. The best results are achieved with Ag‐Al‐SiO2‐p‐Si junctions providing a 12‐nm linewidth and a signal to background ratio of 7:1 at a wavelength of 632.8 nm. The spectral sensitivity of these photodetectors is tunable over the whole visible spectrum either by a variation of the tilt angle or by a dielectric coating.

Surface plasmon enhanced quantum efficiency of metal‐insulator‐semiconductor junctions in the visible

A photodetector that is selective to the polarization, the frequency, and the angle of incident light is presented. Surface plasma modes excited at the surface of a semiconductor–metal–insulator structure provide selective coupling of light into the semiconductor with increased quantum efficiency. Two types of surface modes (TM0 and TE0) are realized by special choices of grating periodicity and insulator film thickness. TM0 modes have a resonant sensitivity to p-polarized light, whereas TE0 modes have a resonant sensitivity to s-polarized light. In addition, for both types of mode the resonance frequency is tunable in a wide range. By combining the selective properties of the surface modes with conventional photodetective devices, we can realize frequency, polarization, and angle-dependent detectors.

W. Beinstingl

Papers

Strongly directional emission from AlGaAs/GaAs light emitting diodes

Polarization-sensitive surface plasmon Schottky detectors.

Surface plasmon polariton enhanced light emission from Schottky diodes

Surface plasmon enhanced quantum efficiency of metal‐insulator‐semiconductor junctions in the visible

Polarization- and wavelength-selective photodetectors