Effects of Localized Heat Generations Due to the Color Conversion in Phosphor Particles and Layers of High Brightness Light Emitting Diodes

2003 ◽  
Author(s):  
Mehmet Arik ◽  
Stanton Weaver ◽  
Charles Becker ◽  
Michael Hsing ◽  
Alok Srivastava
Keyword(s):  
Light Emitting Diodes ◽  
Uv Light ◽  
Numerical Models ◽  
Light Output ◽  
High Brightness ◽  
Light Emitting ◽  
White Leds ◽  
Strong Candidate ◽  
Short Wavelength Light ◽  
Element Technique

The efficiency and reliability of the solid-state lighting devices strongly depend on successful thermal management. Light emitting diodes, LEDs, a strong candidate for the next generation general illumination applications are of interest. Typical white LEDs start with either blue or near UV light generated by the active quantum layers. The light is guided through a transparent encapsulant filled with micron sized phosphor particles. The phosphor particles up-convert the short wavelength light to desired colors, producing white light. Due to low quantum efficiency, during the conversion, localized heating of small particles occurs. Experimental results with high brightness LED packages showed that there is significant light output reduction. Idealized numerical models through Finite element technique were created to evaluate the effects of localized heat generations at particles and layers. Results showed that as small as a 3 mW heat generation on a 20 μm diameter spherical phosphor particle might lead to excessive temperatures which can be a major source of light output degradation and reliability concern for high brightness LEDs.

scholarly journals Full-Color III-Nitride Nanowire Light-Emitting Diodes

2019 ◽  
Vol 3 (4) ◽  
pp. 551 ◽  
Author(s):  
Ravi Teja Velpula ◽  
Barsha Jain ◽  
Ha Quoc Thang Bui ◽  
Hieu Pham Trung Nguyen
Keyword(s):  
Output Power ◽  
Light Emitting Diodes ◽  
Light Output ◽  
Current Status ◽  
Core Shell ◽  
Nonradiative Recombination ◽  
Carrier Distribution ◽  
Light Emitting ◽  
White Leds ◽  
Full Color

III-nitride nanowire-based light-emitting diodes (LEDs) have been intensively studied as promising candidates for future lighting technologies. Compared to conventional GaN-based planar LEDs, III-nitride nanowire LEDs exhibit numerous advantages including greatly reduced dislocation densities, polarization fields, and quantum-conned Stark effect due to the effective lateral stress relaxation, promising high-efficiency full-color LEDs. Beside these advantages, however, several issues have been identified as the limiting factors for further enhancing the nanowire LED quantum efficiency and light output power. Some of the most probable causes have been identified as due to the lack of carrier confinement in the active region, non-uniform carrier distribution, electron overflow, and the nonradiative recombination along the nanowire lateral surfaces. Moreover, the presence of large surface states and defects contribute significantly to the carrier loss in nanowire LEDs. Consequently, reported nanowire LEDs show relatively low output power. Recently, III-nitride core-shell nanowire LED structures have been reported as the most efficient nanowire white LEDs with a record-high output power which is more than 500 times stronger than that of nanowire white LEDs without using core-shell structure. In this context, we will review the current status, challenges, and approaches for the high-performance IIInitride nanowire LEDs. More specifically, we will describe the current methods for the fabrication of nanowire structures including top-down and bottom-up approaches, followed by characteristics of III-nitride nanowire LEDs. We will then discuss the carrier dynamics and loss mechanism in nanowire LEDs. The typical designs for the enhanced performance of III-nitride nanowire LEDs will be presented next. The color-tunable nanowire LEDs with emission wavelengths in the visible spectrum and phosphor-free nanowire white LEDs will be finally discussed.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

scholarly journals Decreasing CCT deviation of white light emitting diodes by employing SiO2 nanoparticles

2021 ◽  
Vol 10 (3) ◽  
pp. 1316-1324
Author(s):  
My Hanh Nguyen Thi ◽  
Phung Ton That
Keyword(s):  
White Light ◽  
Light Emitting Diodes ◽  
Internal Quantum Efficiency ◽  
Light Output ◽  
Sio2 Nanoparticles ◽  
Nano Particles ◽  
Light Extraction Efficiency ◽  
Light Emitting ◽  
White Leds ◽  
White Light Emitting Diodes

In this research, the SiO2 nano-particles (NPs) usage in enhancing optical performances of InGaN/GaN-based white light-emitting diodes (WLEDs) with remote phosphor structure. The research subject shows better lighting capacity than the white LEDs devices without the space between the layers. The adjustment in development process resulted in enhancements of internal quantum efficiency (IQE) and light extraction efficiency (LEE) that lead to 13.5% luminous efficacy improvement. From the experiments, it can be concluded that the LEE is affected by the trapped light and enhancing the light output with SiO2 scattering properties reduce the amount of trapped light. These results confirm that SiO2 nano-particles is effective in enhancing the optical performance of WLEDs and can be considered for production of higher quality devices.

Phosphor Concentration Effects on Optothermal Characteristics of Phosphor Converted White Light-Emitting Diodes

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Jiun Pyng You ◽  
Yeong-Her Lin ◽  
Nguyen T. Tran ◽  
Frank G. Shi
Keyword(s):  
White Light ◽  
Light Emitting Diodes ◽  
Pulse Current ◽  
Light Output ◽  
Constant Current ◽  
Concentration Effects ◽  
Light Emitting ◽  
White Leds ◽  
Physical Mechanisms ◽  
White Light Emitting Diodes

The thermal and optical characteristics of phosphor converted white light-emitting diodes (LEDs) with different phosphor concentrations ranging from 4 wt % to 13 wt % are investigated. The light output of LEDs with higher phosphor concentration is found to have larger degradation in constant current compared with pulse current than that with lower phosphor concentration. In addition, the junction temperatures of phosphor converted white LEDs raise with increasing phosphor concentration, so that the decreased phosphor conversion efficiency is observed both in pulse and constant current modes. The physical mechanisms for these observations are discussed. This study elucidates the phosphor dependent optical and thermal behavior of phosphor converted white LEDs.

Light Output Enhancement of UV Light-Emitting Diodes With Embedded Distributed Bragg Reflector

2011 ◽  
Vol 23 (10) ◽  
pp. 642-644 ◽  
Author(s):  
Bo-Siao Cheng ◽  
Ching-Hsueh Chiu ◽  
Ming-Hua Lo ◽  
Yun-Lin Wu ◽  
Hao-Chung Kuo ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Uv Light ◽  
Light Output ◽  
Bragg Reflector ◽  
Distributed Bragg Reflector ◽  
Light Emitting

scholarly journals Enhanced light output power of near UV light emitting diodes with graphene / indium tin oxide nanodot nodes for transparent and current spreading electrode

2011 ◽  
Vol 19 (23) ◽  
pp. 23111 ◽  
Author(s):  
Tae Hoon Seo ◽  
Kang Jea Lee ◽  
Ah Hyun Park ◽  
Chang-Hee Hong ◽  
Eun-Kyung Suh ◽  
...  
Keyword(s):  
Output Power ◽  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Light Emitting Diodes ◽  
Uv Light ◽  
Light Output ◽  
Light Output Power ◽  
Current Spreading ◽  
Light Emitting

Enhanced light output of GaN-based near-UV light-emitting diodes by using nanopatterned indium tin oxide electrodes

2006 ◽  
Vol 21 (5) ◽  
pp. 594-597 ◽  
Author(s):  
Hyun-Gi Hong ◽  
Seok-Soon Kim ◽  
Dong-Yu Kim ◽  
Takhee Lee ◽  
June-O Song ◽  
...  
Keyword(s):  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Light Emitting Diodes ◽  
Uv Light ◽  
Light Output ◽  
Light Emitting ◽  
Oxide Electrodes

Low-Temperature Operation of Green, Blue and UV InGaN/GaN Multiple-Quantum-Well Light-Emitting Diodes

2003 ◽  
Vol 764 ◽  
Author(s):  
X. A. Cao ◽  
S. F. LeBoeuf ◽  
J. L. Garrett ◽  
A. Ebong ◽  
L. B. Rowland ◽  
...  
Keyword(s):  
Quantum Well ◽  
Light Emitting Diodes ◽  
Multiple Quantum Well ◽  
Light Output ◽  
Localized States ◽  
Multiple Quantum ◽  
Nonradiative Recombination ◽  
Light Emitting ◽  
Temperature Range ◽  
Green Leds

Absract:Temperature-dependent electroluminescence (EL) of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with peak emission energies ranging from 2.3 eV (green) to 3.3 eV (UV) has been studied over a wide temperature range (5-300 K). As the temperature is decreased from 300 K to 150 K, the EL intensity increases in all devices due to reduced nonradiative recombination and improved carrier confinement. However, LED operation at lower temperatures (150-5 K) is a strong function of In ratio in the active layer. For the green LEDs, emission intensity increases monotonically in the whole temperature range, while for the blue and UV LEDs, a remarkable decrease of the light output was observed, accompanied by a large redshift of the peak energy. The discrepancy can be attributed to various amounts of localization states caused by In composition fluctuation in the QW active regions. Based on a rate equation analysis, we find that the densities of the localized states in the green LEDs are more than two orders of magnitude higher than that in the UV LED. The large number of localized states in the green LEDs are crucial to maintain high-efficiency carrier capture at low temperatures.

Performance of vertical type deep UV light-emitting diodes depending on the Ga-face n-contact hole density

2021 ◽  
Vol 118 (23) ◽  
pp. 231102
Author(s):  
Youn Joon Sung ◽  
Dong-Woo Kim ◽  
Geun Young Yeom ◽  
Kyu Sang Kim
Keyword(s):  
Light Emitting Diodes ◽  
Uv Light ◽  
Hole Density ◽  
Light Emitting ◽  
Deep Uv

scholarly journals Improved Performance of GaN-Based Light-Emitting Diodes Grown on Si (111) Substrates with NH3 Growth Interruption

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 399
Author(s):  
Sang-Jo Kim ◽  
Semi Oh ◽  
Kwang-Jae Lee ◽  
Sohyeon Kim ◽  
Kyoung-Kook Kim
Keyword(s):  
Buffer Layer ◽  
Light Emitting Diodes ◽  
Defect Density ◽  
Strain Relaxation ◽  
Multiple Quantum Well ◽  
Light Output ◽  
Multiple Quantum ◽  
Light Emitting ◽  
Growth Interruption ◽  
Aln Buffer

We demonstrate the highly efficient, GaN-based, multiple-quantum-well light-emitting diodes (LEDs) grown on Si (111) substrates embedded with the AlN buffer layer using NH3 growth interruption. Analysis of the materials by the X-ray diffraction omega scan and transmission electron microscopy revealed a remarkable improvement in the crystalline quality of the GaN layer with the AlN buffer layer using NH3 growth interruption. This improvement originated from the decreased dislocation densities and coalescence-related defects of the GaN layer that arose from the increased Al migration time. The photoluminescence peak positions and Raman spectra indicate that the internal tensile strain of the GaN layer is effectively relaxed without generating cracks. The LEDs embedded with an AlN buffer layer using NH3 growth interruption at 300 mA exhibited 40.9% higher light output power than that of the reference LED embedded with the AlN buffer layer without NH3 growth interruption. These high performances are attributed to an increased radiative recombination rate owing to the low defect density and strain relaxation in the GaN epilayer.

New Results on Electroluminescence from Porous Silicon

1992 ◽  
Vol 283 ◽  
Author(s):  
Peter Steiner ◽  
Frank Kozlowski ◽  
Hermann Sandmaier ◽  
Walter Lang
Keyword(s):  
Porous Silicon ◽  
Quantum Efficiency ◽  
Light Emitting Diodes ◽  
Uv Light ◽  
Green Light ◽  
Light Emitting ◽  
Porous Region ◽  
First Results

ABSTRACTFirst results on light emitting diodes in porous silicon were reported in 1991. They showed a quantum efficiency of 10-7 to 10-5 and an orange spectrum. Over the last year some progress was achieved:- By applying UV-light during the etching blue and green light emitting diodes in porous silicon are fabricated.- When a p/n junction is realized within the porous region, a quantum efficiency of 10-4 is obtained.

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