• Title/Summary/Keyword: Efficiency droop

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Temperature Dependence of Efficiency Droop in GaN-based Blue Light-emitting Diodes from 20 to 80℃

  • Ryu, Guen-Hwan;Seo, Dong-Joo;Ryu, Han-Youl
    • Current Optics and Photonics
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    • v.2 no.5
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    • pp.468-473
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    • 2018
  • We investigate the temperature dependence of efficiency droop in InGaN/GaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) in the temperature range from 20 to $80^{\circ}C$. When the external quantum efficiency (EQE) and the wall-plug efficiency (WPE) of the LED sample were measured as injection current and temperature varied, the droop of EQE and WPE was found to be reduced with increasing temperature. As the temperature increased from 20 to $80^{\circ}C$, the droop ratio of EQE was decreased from 16% to 14%. This reduction in efficiency droop with temperature can be interpreted by a temperature-dependent carrier distribution in the MQWs. When the carrier distribution and radiative recombination rate in MQWs were simulated and compared for different temperatures, the carrier distribution was found to become increasingly homogeneous as the temperature increased, which is believed to partly contribute to the reduction in efficiency droop with increasing temperature.

The Improvement of Droop Characteristic of 780nm Monolithic 4-Beam Laser Diode (780nm Monolithic 4-Beam 레이저 다이오드의 Droop 특성 개선)

  • Hong, Hyun-Kwon;Kim, Ji-Ho;Ji, You-Sang;Seong, Yeong-Un;Lee, Sang-Don
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2009.06a
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    • pp.285-287
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    • 2009
  • When the laser diode is operated with continuous current, the light intensity from the laser diode deceases with time due to the temperature rise in the active layer. The phenomena, which is often called as DROOP, should be minimized in order to be used as a light source for the laser beam printer. We experimently examined the influences of the laser parameters such as threshold current, differential quantum efficiency on droop. It was found that decreasing the differential quantum efficiency of the laser diode is the effective way to minimize droop.

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4181Overcoming the High-current Efficiency Loss Mechanism in GaN-based Light-emitting Diodes

  • Kim, Jong-Gyu
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2011.05a
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    • pp.23.2-23.2
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    • 2011
  • This presentation will include an overview of III-Nitride LED technology, applications, key areas for future improvements, challenges such as efficiency droop. GaN-based high-power light-emitting diodes (LEDs) suffer from high-current loss mechanisms that lead to a significant decrease in internal quantum efficiency at high drive currents, a well-known phenomenon commonly referred to as efficiency droop. Although many attempts have been made to uncover this LED's darkest secret, there is still a lack of consensus on the dominant mechanism responsible for this detrimental phenomenon. In this presentation, proposed origins and corresponding solutions to the droop-causing mechanisms will be reviewed and discussed.

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Development of 80kW Bi-directional Hybrid-SiC Boost-Buck Converter using Droop Control in DC Nano-grid (DC 나노그리드에서 Droop제어를 적용한 80kW급 양방향 하이브리드-SiC 부스트-벅 컨버터 개발)

  • Kim, Yeon-Woo;Kwon, Min-Ho;Park, Sung-Youl;Kim, Min-Kook;Yang, Dae-Ki;Choi, Se-Wan;Oh, Seong-Jin
    • The Transactions of the Korean Institute of Power Electronics
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    • v.22 no.4
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    • pp.360-368
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    • 2017
  • This paper proposes the 80-kW high-efficiency bidirectional hybrid SiC boost/buck converter using droop control for DC nano-grid. The proposed converter consists of four 20-kW modules to achieve fault tolerance, ease of thermal management, and reduced component stress. Each module is constructed as a cascaded structure of the two basic bi-directional converters, namely, interleaved boost and buck converters. A six-pack hybrid SiC intelligent power module (IPM) suitable for the proposed cascaded structure is adopted for high-efficiency and compactness. The proposed converter with hybrid switching method reduces the switching loss by minimizing switching of insulated gate bipolar transistor (IGBT). Each module control achieves smooth transfer from buck to boost operation and vice versa, since current controller switchover is not necessary. Furthermore, the proposed parallel control using DC droop with secondary control, enhances the current sharing accuracy while well regulating the DC bus voltage. A 20-kW prototype of the proposed converter has been developed and verified with experiments and indicates a 99.3% maximum efficiency and 98.8% rated efficiency.

Convex Optimization Approach to Multi-Level Modulation for Dimmable Visible Light Communications under LED Efficiency Droop

  • Lee, Sang Hyun;Park, Il-Kyu;Kwon, Jae Kyun
    • Journal of the Optical Society of Korea
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    • v.20 no.1
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    • pp.29-35
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    • 2016
  • This paper deals with a design method and capacity loss of an efficient multi-level modulation scheme for dimmable visible light communications (VLC) systems that use light-emitting diodes (LEDs) with efficiency droop. To this end, the impact of such an impairment on dimmable VLC is addressed with respect to multi-level modulations based on pulse-amplitude modulation (PAM) via data-rate optimization formulation.

Coordinated Droop Control for Stand-alone DC Micro-grid

  • Kim, Hyun-Jun;Lee, Yoon-Seok;Kim, Jae-Hyuk;Han, Byung-Moon
    • Journal of Electrical Engineering and Technology
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    • v.9 no.3
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    • pp.1072-1079
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    • 2014
  • This paper introduces a coordinated droop control for the stand-alone DC micro-grid, which is composed of photo-voltaic generator, wind power generator, engine generator, and battery storage with SOC (state of charge) management system. The operation of stand-alone DC micro-grid with the coordinated droop control was analyzed with computer simulation. Based on simulation results, a hardware simulator was built and tested to analyze the performance of proposed system. The developed simulation model and hardware simulator can be utilized to design the actual stand-alone DC micro-grid and to analyze its performance. The coordinated droop control can improve the reliability and efficiency of the stand-alone DC micro-grid.

A Novel Droop Control Method to Minimize Distribution Loss in DC Microgrid (DC 마이크로그리드의 배전 손실 최소화를 위한 새로운 드룹 제어 기법)

  • Kim, Seok-Woong;Choi, See-Young;Kim, Rae-Young
    • Proceedings of the KIPE Conference
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    • 2015.07a
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    • pp.371-372
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    • 2015
  • Dc microgrid has the advantage of high efficiency as compared to the ac system. Droop method has been realized to suppress the current mismatching among the distributed sources. However, this method involves distribution loss due to the line impedance. In this paper, a novel droop method is proposed to minimize the distribution loss as well as the voltage deviation by adjusting the droop coefficient. The proposed droop method is verified by using the simulation based on PSCAD/EMTDC.

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Reducing Efficiency Droop in (In,Ga)N/GaN Light-emitting Diodes by Improving Current Spreading with Electron-blocking Layers of the Same Size as the n-pad

  • Pham, Quoc-Hung;Chen, Jyh-Chen;Nguyen, Huy-Bich
    • Current Optics and Photonics
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    • v.4 no.4
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    • pp.380-390
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    • 2020
  • In this study, the traditional electron-blocking layer (EBL) in (In,Ga)N/GaN light-emitting diodes is replaced by a circular EBL that is the same size as the n-pad. The three-dimensional (3D) nonlinear Poisson, drift-diffusion, and continuity equations are adopted to simulate current transport in the LED and its characteristics. The results indicate that the local carrier-density distribution obtained for the circular EBL design is more uniform than that for the traditional EBL design. This improves the uniformity of local radiative recombination and local internal quantum efficiency (IQE) at high injection levels, which leads to a higher lumped IQE and lower efficiency droop. With the circular EBL, the lumped IQE is higher in the outer active region and lower in the active region under the n-pad. Since most emissions from the active region under the n-pad are absorbed by the n-pad, obviously, an LED with a circular EBL will have a higher external quantum efficiency (EQE). The results also show that this LED works at lower applied voltages.

Study on Efficiency Droop in a-plane InGaN/GaN Light Emitting Diodes

  • Song, Hoo-Young;Suh, Joo-Young;Kim, Eun-Kyu;Baik, Kwang-Hyeon;Hwang, Sung-Min;Yun, Joo-Sun;Shim, Jong-In
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.02a
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    • pp.145-145
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    • 2011
  • Light-emitting diodes (LEDs) based on III-nitrides compound semiconductors have achieved a high performance device available for display and illumination sector. However, the conventional c-plane oriented LED structures are still showing several problems given by the quantum confined Stark effect (QCSE) due to the effects of strong piezoelectric and spontaneous polarizations. The QCSE results in spatial separation of electron and hole wavefunctions in quantum wells, thereby decreasing the internal quantum efficiency and red-shifting the emission wavelength. Due to demands for improvement of device performance, nonpolar structure has been attracting attentions, since the quantum wells grown on nonpolar templates are free from the QCSE. However, current device performance for nonpolar LEDs is still lower than those for conventional LEDs. In this study, we discuss the potential possibilities of nonpolar LEDs for commercialization. In this study, we characterized current-light output power relation of the a-plane InGaN/GaN LEDs structures with the variation of quantum well structures. On-wafer electroluminescence measurements were performed with short pulse (10 us) and low duty factor (1 %) conditions applied for eliminating thermal effects. The well and barrier widths, and indium compositions in quantum well structures were changed to analyze the efficiency droop phenomenon.

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Characterization of Optical Properties of Light-Emitting Diodes Grown on Si (111) Substrate with Different Quantum Well Numbers and Thicknesses

  • Jang, Min-Ho;Go, Yeong-Ho;Go, Seok-Min;Yu, Yang-Seok;Kim, Jun-Yeon;Tak, Yeong-Jo;Park, Yeong-Su;Jo, Yong-Hun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.313-313
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    • 2012
  • In recent years there have been many studies of InGaN/GaN based light emitting diodes (LEDs) in order to progress the performance of luminescence. Many previous literatures showed the performance of LEDs by changing the LED structures and substrates. However, the studies carried out by the researchers so far were very complicated and sometimes difficult to apply in practice. Therefore, we propose one simple method of changing the thickness and the numbers of multiple quantum wells (MQWs) in order to optimize their effects. In our research, we investigated electrical and optical properties by changing the well thickness and the number of quantum well (QW) pair in LED structures by growing the structure -inch Si (111) wafer. We defined the samples from LED_1 to LED_3 according to MQW structure. Samples LED_1, LED_2 and LED_3 consist of 5-pair InGaN/GaN (3.5 nm/ 4.5 nm), 5-pair InGaN/GaN (3 nm/4.5 nm) and 7-pair InGaN/GaN (3.5 nm/4.5 nm), respectively. We characterized electrical and optical properties by using electroluminescence (EL) measurement. Also, Efficiency droop was analyzed by calculating external quantum efficiency (EQE) with varying injection current. The EL spectra of three samples show different emission wavelength peaks, FWHM and the blueshift of wavelength caused by screening the internal electric field because of the effect of different MQW structure. The results of optical properties show that the LED_2 sample reduce the internal electric field in QW than LED_1 from EL spectra. the increase in the number of QW pairs reduces the strain and increase the In composition in MQW. And, the points of efficiency droop's peak show different trend from LED_1 to LED_3. It is related with the carrier density in active region. Thus, from the results of experiments, we are able to achieve high performance LEDs and a reduction of efficiency droop and emission wavelength blueshift by optimizing MQWs structure.

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