Browsing by Author "Fu, Yi-Keng"

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Effect of AlInGaN barrier layers with various TMGa flows on optoelectronic characteristics of near UV light-emitting diodes grown by atmospheric pressure metalorganic vapor phase epitaxy
(2011-08-01)
Fu, Yi-Keng
;
Lu, Yu-Hsuan
;
Jiang, Ren-Hao
;
Chen, Bo-Chun
;
Fang, Yen-Hsiang
Near ultraviolet light-emitting diodes (LEDs) with quaternary AlInGaN quantum barriers (QBs) are grown by atmospheric pressure metalorganic vapor phase epitaxy. The indium mole fraction of AlInGaN QB could be enhanced as we increased the TMG flow rate. Both the wavelength shift in EL spectra and forward voltage at 20 mA current injection were reduced by using AlInGaN QB. Under 100 mA current injection, the LED output power with Al(0.089)In(0.035)Ga(0.876)N QB can be enhanced by 15.9%, compared to LED with GaN QB. It should be attributed to a reduction of lattice mismatch induced polarization mismatch in the active layer. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
High efficiency and output power of near-ultraviolet light-emitting diodes grown on GaN substrate with back-side etching
(2012-04-01)
Fang, Yen-Hsiang
;
Fu, Yi-Keng
;
Xuan, Rong
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電子物理學系
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Department of Electrophysics
In this paper, we investigate the differences between optical and electrical properties of near-ultraviolet (NUV) InGaN/GaN multi-quantum well light-emitting diodes (LEDs) grown on GaN substrate with a roughened back-side on the N-face surface of GaN substrate through a chemical wet-etching process, and on pattern sapphire substrate (PSS). Back-side etching-treated NUV-LEDs have larger output power than conventional NUV-LEDs, NUV-LEDs with wider wells and NUV-LEDs grown on PSS. When the NUV-LEDs were operated at a forward current of 20 mA, the output power of back-side etching-treated NUV-LEDs was improved by approximately 100, 106 and 8% compared with that of conventional NUV-LEDs, NUV-LEDs with wider wells and NUV-LEDs grown on PSS, respectively. This larger enhancement results from the improved light extraction that was attributed to the different transmittance because a hexagonal pyramid on the N-face GaN that was etched formed at the stable crystallographic etching planes of the GaN {1011} planes.
Hole Injection and Electron Overflow Improvement in 365 nm Light-Emitting Diodes by Band-Engineering Electron Blocking Layer
(2013-08-01)
Fu, Yi-Keng
;
Lu, Yu-Hsuan
;
Xuan, Rong
;
Chen, Jenn-Fang
;
Su, Yan-Kuin
The work reports a theoretical and experimental study on the device performance of near ultraviolet light-emitting diodes (LEDs) with specific design on the electron blocking layer (EBL) by employing the band-engineering. The simulation results show the polarization-induced downward band bending is mitigated in the specific EBL design and, hence, the capability of hole transportation increases and the behavior of electron overflow decreases. The experimental results show the LEDs with specific EBL design exhibited a reduction of forward voltage from 4.40 to 4.07 V and a much enhancement of light output power from 30.6 to 51.9mW, compared with conventional LED. (C) 2013 The Japan Society of Applied Physics
Improved Performance of InGaN/GaN Light-Emitting Diodes With Thin Intermediate Barriers
(2011-11-15)
Chen, Bo-Chun
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Chang, Chun-Yen
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Fu, Yi-Keng
;
Huang, Kai-Feng
;
Lu, Yu-Hsuan
In this work, the performance of blue InGaN/GaN light-emitting diodes (LEDs) with thin intermediate barriers at high injection current is investigated. From the experimental results, it is found that the performance of LEDs with intermediate 5-nm-thick barriers is improved about 15% at 200 mA, compared with the sample with unique 9-nm-thick barriers. A numerical study is executed to analyze the hole distributions in the quantum wells. From the simulated results, it is found that the hole injection efficiency can be improved at high injection current. Hence, the effective recombination of electron and hole is also enhanced at high injection current.
Optical Simulation and Fabrication of Near-Ultraviolet LEDs on a Roughened Backside GaN Substrate
(2012-03-15)
Fu, Yi-Keng
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Lu, Yu-Hsuan
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Xuan, Rong
;
Chao, Chia-Hsin
;
Su, Yan-Kuin
In this letter, the numerical and experimental demonstrations for enhancement of light extraction efficiency in near-ultraviolet light-emitting diodes (LEDs) with a roughened backside on the N-face surface of GaN substrate through a chemical wet-etching process are investigated. It was also found that the increased etching time can increase the height of hexagonal pyramids and decrease the density of hexagonal pyramids. With 20-mA injection current, it was found that forward voltages were 3.13 and 3.16 V while output powers were 13.15 and 27.18 mW for the conventional LED and roughened backside LED, respectively.
Study of InGaN-Based Light-Emitting Diodes on a Roughened Backside GaN Substrate by a Chemical Wet-Etching Process
(2011-10-01)
Fu, Yi-Keng
;
Chen, Bo-Chun
;
Fang, Yen-Hsiang
;
Jiang, Ren-Hao
;
Lu, Yu-Hsuan
The InGaN-based light-emitting diodes (LEDs) with a roughened backside on the N-face surface of GaN substrate were fabricated through a chemical wet-etching process to increase light-extraction efficiency. The stable crystallographic etching planes were formed as the GaN {10 (11) over bar} planes. When the near-ultraviolet and blue LED were operated as a forward current of 20 mA, the output power of LEDs was improved from 13.2 and 19.9 mW to 25.6 and 24.0 mW, respectively. The different enhanced ratio is attributed to the different transmittance as a function of wavelength is caused from hexagonal pyramid on N-face GaN substrate after wet-etching process.
The effect of trimethylgallium flows in the AIInGaN barrier on optoelectronic characteristics of near ultraviolet light-emitting diodes grown by atmospheric pressure metalorganic vapor phase epitaxy
(2011-03-21)
Fu, Yi-Keng
;
Jiang, Ren-Hao
;
Lu, Yu-Hsuan
;
Chen, Bo-Chun
;
Xuan, Rong
The letter reports a theoretical and experimental study on the device performance of near ultraviolet light-emitting diodes (LEDs) with quaternary AlInGaN quantum barrier (QB). The indium mole fraction of AlInGaN QB could be enhanced as we increased the trimethylgallium flow rate. It was found the AlInGaN/InGaN LEDs can reduce forward voltage and improve light output power, compared with conventional GaN QB. By using advanced device simulation, it should be attributed to a reduction in lattice mismatch induced polarization mismatch in the active layer, which results in the suppression of electron overflow. (C) 2011 American Institute of Physics. [doi:10.1063/1.3571440]
Transparent electrode design for AlGaN deep-ultraviolet light-emitting diodes
(2017-12-11)
Hrong, Ray-Hua
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Zeng, Yu-Yuan
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Wang, Wei-Kai
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Tsai, Chia-Lung
;
Fu, Yi-Keng
Zinc gallate (ZnGa2O4; ZGO) thin films were employed as the p-type transparent contact layer in deep-ultraviolet AlGaN-based light-emitting diodes (LEDs) to increase light output power. The transmittance of 200-nm-thick ZGO in deep-ultraviolet wavelength (280 nm) was as high as 92.3%. Two different ohmic contact structures, a dot-LED (D-LED; ZGO/dot-ITO/LED) and whole-LED (W-LED; ZGO/ITO/LED), exhibited improved light output power and current spreading compared to a conventional ITO-LED (C-LED). At an injection current of 20 mA, the D-LED and W-LED exhibited 33.7% and 12.3% enhancements in light output power, respectively, compared to the C-LED. The enhanced light output power of the D-LED can be attributed to an improvement in current spreading and enhanced light-extracting efficiency achieved by introducing ZGO/dot-ITO. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement