Bridging the “green gap” of LEDs: giant light output enhancement and directional control of LEDs via embedded nano-void photonic crystals

Tsai, Yu Lin; Liu, Che Yu; Krishnan, Chirenjeevi; Lin, Da-Wei; Chu, You Chen; Chen, Tzu Pei; Shen, Tien Lin; Kao, Tsung Sheng; Charlton, Martin D. B.; Yu, Peichen; Lin, Chien-Chung; Kuo, Hao‐Chung; He, Jr Hau

doi:10.1039/c5nr05555e

Cited by 24 publications

(15 citation statements)

References 43 publications

(53 reference statements)

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“…Additionally, highly strained InGaN/GaN green multiple quantum wells (MQWs), due to a large lattice mismatch between the high-In-content InGaN and the GaN, exhibit strong piezoelectric-field-induced quantum-confined stark effects (QCSE), resulting in a spatial separation of the wave functions of electrons and holes in the quantum well [ 15 , 16 ]. In the past few decades, much scientific effort has focused on approaches to improve the optical and electrical properties of green LEDs [ 17 , 18 , 19 ]. It was found that hexagonal V-pits having inverted pyramids with (10-11) faceted sidewalls were generally formed in InGaN/GaN MQWs [ 20 , 21 , 22 , 23 ].…”

Section: Introductionmentioning

confidence: 99%

An InGaN/GaN Superlattice to Enhance the Performance of Green LEDs: Exploring the Role of V-Pits

et al. 2018

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Despite the fact that an InGaN/GaN superlattice (SL) is useful for enhancing the performance of a GaN-based light-emitting diode (LED), its role in improving the efficiency of green LEDs remains an open question. Here, we investigate the influence of a V-pits-embedded InGaN/GaN SL on optical and electrical properties of GaN-based green LEDs. We recorded a sequence of light emission properties of InGaN/GaN multiple quantum wells (MQWs) grown on a 0- and 24-pair InGaN/GaN SL by using scanning electron microscopy (SEM) in combination with a room temperature cathodoluminescence (CL) measurement, which demonstrated the presence of a potential barrier formed by the V-pits around threading dislocations (TDs). We find that an increase in V-pit diameter would lead to the increase of V-pit potential barrier height. Our experimental data suggest that a V-pits-embedded, 24-pair InGaN/GaN SL can effectively suppress the lateral diffusion of carriers into non-recombination centers. As a result, the external quantum efficiency (EQE) of green LEDs is improved by 29.6% at an injection current of 20 mA after implementing the V-pits-embedded InGaN/GaN SL layer. In addition, a lower reverse leakage current was achieved with larger V-pits.

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Section: Introductionmentioning

confidence: 99%

An InGaN/GaN Superlattice to Enhance the Performance of Green LEDs: Exploring the Role of V-Pits

et al. 2018

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“…However, room for improvement remains, including the internal quantum efficiency of the active region [5,6], the light-extraction technology [7], the current-flow design [8], the minimization of resistive loss [9], the electrostatic discharge stability [10], and the color-rendering property via the color mixing [11]. Aside from these improvements, various stress-inducing degradation tests, by means of temperature, current, static charge, optical radiation, and moisture, have been developed [12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Multi-Azimuth Failure Mechanisms in Phosphor-Coated White LEDs by Current Aging Stresses

Peng

Guo

et al. 2018

Applied Sciences

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We have experimentally analyzed multi-azimuth degradation mechanisms that govern failures of commercially-available high-power (1 Watt) phosphor-coated white (hppc-W) light-emitting diodes (LEDs) covered with peanut-shaped lenses under three current-stress aging (CSA) conditions. Comprehensive analyses focus on photometric, chromatic, electrical, thermal and packaging characteristics. At the packaging level, (a) the decrease of the phosphor-conversion efficiency; (b) the yellow-browning of the optical lens; and (c) the darkening of the silver-coated reflective layer deposited with extraneous chemical elements (e.g., C, O, Si, Mg, and Cu, respectively) contribute collectively to the integral degradation of the optical power. By contrast, Ohmic contacts, thermal properties, and angles of maximum intensity remain unchanged after 3840 h aging in three cases. Particularly at the chip level, the formation of point defects increases the number of non-radiative recombination centers, and thus decreases the optical power during aging stages. Nevertheless, in view of the change of the ideality factor, the Mg dopant activation and the annealing effect facilitate the increase of the optical power in two specific aging stages (192 h~384 h and 768 h~1536 h). This work offers a systematic guidance for the development of reliable LED-based light sources in general-lighting areas.

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“…Then the lattice constant a P hCs of the embedded PhCs was kept at 498 nm, radius R P hCs set as 150 nm, and depth fixed at 500 nm for the time being, which have been used to improve the LEDs green light output performance in [18]. We could calculate the filling factor from Equation (6), that was about 0.33.…”

Section: The Dependence Of Lee On the Distance Between Embedded Phcs mentioning

confidence: 99%

“…Recently, PhCs and nano-array surfaces have shown great potential in the improvement of LEE. Tsai et al [18] have fabricated embedded PhCs within the GaN/InGaN green LEDs to enhance the LEE of LEDs by 78%, and meanwhile, the view angle of LEDs has also been collimated from 131.5 • to 114.0 • . Chen et al [19] have used nano-pillar array to improve the LEE of GaN-based blue LEDs and achieved a factor of 1.41 enhancement at 20 mA current injection.…”

Section: Introductionmentioning

confidence: 99%

Using Three-Component Hierarchical Structures to Improve the Light Extraction From White Leds Based on Red-Green-Blue Color Mixing Method

Li¹,

Li²,

Kong³

et al. 2017

PIER C

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Abstract-In this work, we present a three-component hierarchical structure to simultaneously improve the red, green, and blue (RGB) light extraction efficiency (LEE) of white light-emitting diodes (LEDs) based on color mixing method. With the help of 3D finite-difference time-domain (FDTD) simulations, the effects of the embedded photonic crystals (PhCs) the normal surface PhCs and the nano-rods on the enhancement of RGB light extraction were investigated. The results were compared with those of the conventional planar LEDs and the normal surface PhCs LEDs over the whole visible spectrum. Results from the simulations demonstrated that the maximum LEE for the hierarchical structures LEDs gave 112%, 327%, and 284% RGB LEE enhancement, respectively, compared to that of the conventional planar LEDs, and achieved 104%, 191%, and 187% RGB LEE enhancement compared to that of LEDs with normal surface PhCs. The emission characteristics of the hierarchical structures LEDs were also revealed in detail by FDTD simulations. The results shown in this paper would do a favor for the design and fabrication of high efficiency LEDs.

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Bridging the “green gap” of LEDs: giant light output enhancement and directional control of LEDs via embedded nano-void photonic crystals

Cited by 24 publications

References 43 publications

An InGaN/GaN Superlattice to Enhance the Performance of Green LEDs: Exploring the Role of V-Pits

An InGaN/GaN Superlattice to Enhance the Performance of Green LEDs: Exploring the Role of V-Pits

Multi-Azimuth Failure Mechanisms in Phosphor-Coated White LEDs by Current Aging Stresses

Using Three-Component Hierarchical Structures to Improve the Light Extraction From White Leds Based on Red-Green-Blue Color Mixing Method

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