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Proceedings ArticleDOI

Further Enhancement of Directional Light Extraction Efficiency of LED in Infrared Region using Triangular Nanophotonic Crystals of Different Composite Materials

13 Dec 2014-Photonics (Optical Society of America)-

AbstractImprovement of ‘Light Extraction Efficiency’ in LED using triangular nano-patterned layers of different composite materials has been studied. The mathematical formulations for the coupling of light modes are discussed while analysis is done using FDTD method.

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References
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Journal ArticleDOI
TL;DR: The results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.
Abstract: 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.

1,312 citations

Journal ArticleDOI
TL;DR: It is shown how one can thereby compute semianalytical reflection and transmission through crystal tapers of almost any length, using only a single pair of modes in the unit cells of uniform gratings, which becomes more accurate as the taper becomes more gradual, with no significant increase in the computation time or memory.
Abstract: We prove that an adiabatic theorem generally holds for slow tapers in photonic crystals and other strongly grated waveguides with arbitrary index modulation, exactly as in conventional waveguides. This provides a guaranteed pathway to efficient and broad-bandwidth couplers with, e.g., uniform waveguides. We show that adiabatic transmission can only occur, however, if the operating mode is propagating (nonevanescent) and guided at every point in the taper. Moreover, we demonstrate how straightforward taper designs in photonic crystals can violate these conditions, but that adiabaticity is restored by simple design principles involving only the independent band structures of the intermediate gratings. For these and other analyses, we develop a generalization of the standard coupled-mode theory to handle arbitrary nonuniform gratings via an instantaneous Bloch-mode basis, yielding a continuous set of differential equations for the basis coefficients. We show how one can thereby compute semianalytical reflection and transmission through crystal tapers of almost any length, using only a single pair of modes in the unit cells of uniform gratings. Unlike other numerical methods, our technique becomes more accurate as the taper becomes more gradual, with no significant increase in the computation time or memory. We also include numerical examples comparing to a well-established scattering-matrix method in two dimensions.

255 citations

Journal ArticleDOI
Abstract: We relate the currently limited efficiency of photonic crystal (PhC)-assisted gallium nitride light-emitting diodes (LEDs) to the existence of unextracted guided modes. To remedy this, we introduce epitaxial structures which modify the distribution of guided modes. LEDs are fabricated according to this concept, and the tailored band structure is determined experimentally. We investigate theoretically the consequences of this improvement, which significantly enhances the potential for efficient light extraction by PhCs.

198 citations

Journal ArticleDOI
Abstract: In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications.

86 citations

Journal ArticleDOI
Abstract: Highly efficient extraction of photoluminescence is observed from two-dimensional photonic crystal slabs employing InGaAs quantum dots as active material. The introduction of quantum dots reduces diffusion of carriers and thereby suppresses the surface recombination at the air-hole sidewalls of the photonic crystal. Around the normalized frequency of 0.7, over thirty-fold enhancement of the photoluminescence extraction is achieved at 78 K, indicating strong coupling to leaky modes of the free-standing photonic crystal slab. In addition, when the photoluminescence spectra overlaps with a photonic band gap, enhanced light extraction originating from the photonic band gap is observed experimentally.

72 citations