Browsing by Author "Kuo, Yen-Kuang"

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A Simulation-Based LED Design Project in Photonics Instruction Based on Industry-University Collaboration
(2011-11-01)
Chang, Shu-Hsuan
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Chen, Mei-Ling
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Kuo, Yen-Kuang
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Shen, Yung-Chi
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科技管理研究所
In response to the growing industrial demand for light-emitting diode (LED) design professionals, based on industry-university collaboration in Taiwan, this paper develops a novel instructional approach: a simulation-based learning course with peer assessment to develop students' professional skills in LED design as required by industry as well as to enhance cognition and metacognition in students in higher education. The simulation-based learning course enables students to understand the influences on LED performance of the variation of different parameters and to seek the best design through comparing the effectiveness of different combinations of parameters. The evaluation results of pre- and post-test knowledge maps and a photonics scoreboard indicate that this project-based instruction may help students understand the operating principles of LEDs and enhance their skill in LED design. The Constructivist Project-based Learning Environment Survey is adopted to demonstrate that the proposed project-based learning environment is beneficial in cultivating student inquiry learning, reflective thinking, teamwork, and skills in creative problem solving.
Effects of built-in polarization and carrier overflow on InGaN quantum-well lasers with electronic blocking layers
(2008-01-01)
Chen, Jun-Rong
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Lee, Chung-Hsien
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Ko, Tsung-Shine
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Chang, Yi-An
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Lu, Tien-Chang
Effects of built-in polarization and carrier overflow on InGaN quantum-well lasers with a ternary AlGaN or a quaternary AlInGaN electronic blocking layer (EBL) have been numerically investigated by employing an advanced device-simulation program. The simulation results indicate that the characteristics of InGaN quantum-well lasers can be improved by using the quaternary AlInGaN EBL. When the aluminum and indium compositions in the AlInGaN EBL are appropriately designed, the built-in charge density at the interface between the InGaN barrier and the AlInGaN EBL can be reduced. Under this circumstance, the electron leakage current and the laser threshold current can obviously be decreased as compared with the laser structure with a conventional AlGaN EBL when the built-in polarization is taken into account in the calculation. Furthermore, the AlInGaN EBL also gives a higher refractive index than the AlGaN EBL, which is a benefit for a higher quantum-well optical confinement factor in laser operations.
Experimental and theoretical analysis on ultraviolet 370 nm AlGaInN light-emitting diodes
(2006-05-01)
Chang, Yi-An
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Yen, Sheng-Horng
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Wang, Te-Chung
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Kuo, Hao-Chung
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Kuo, Yen-Kuang
An ultraviolet (UV) AlGaInN light-emitting diode (LED) with 370 nm emission is demonstrated. At room temperature (RT) UV power of 0.8 mW at 20 mA with 3.6 V operation voltage is achieved. It provides 4 mW output when driven at 125 mA under continuous-wave (CW) operation. Qualitative optimization of the Al composition in the AlGaN electron-block layer and the quaternary AlGaInN quantum well (QW) number of the UV LED is also investigated in this study. The numerical results fit with the experimentally demonstrated output performance of our AlGaInN UV LED. We find that the UV AlGaInN LED can provide better output characteristics when the Al composition in the AlGaN electron-block layer is in the range 19-21 % and the AlGaInN QW number is in the range 5-7 by reducing the electron leakage current.
Fabrication and characterization of back-side illuminated InGaN/GaN solar cells with periodic via-holes etching and Bragg mirror processes
(2014-08-25)
Chang, Yi-An
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Chen, Fang-Ming
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Tsai, Yu-Lin
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Chang, Ching-Wen
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Chen, Kuo-Ju
In this study, the design and fabrication schemes of back-side illuminated InGaN/GaN solar cells with periodic via-holes etching and Bragg mirror processes are presented. Compared to typical front-side illuminated solar cells, the improvements of open-circuit voltage (V-oc) from 1.88 to 1.94 V and short-circuit current density (J(sc)) from 0.84 to 1.02 mA/cm(2) are observed. Most significantly, the back-side illuminated InGaN/GaN solar cells exhibit an extremely high fill factor up to 85.5%, leading to a conversion efficiency of 1.69% from 0.66% of typical front-side illuminated solar cells under air mass 1.5 global illuminations. Moreover, the effects of bottom Bragg mirrors on the photovoltaic characteristics of back-side illuminated solar cells are studied by an advanced simulation program. The results show that the J(sc) could further be improved with a factor of 10% from the original back-side illuminated solar cell by the structure optimization of bottom Bragg mirrors. (C) 2014 Optical Society of America
Fabrication and Characterization of Temperature Insensitive 660-nm Resonant-Cavity LEDs
(2008-07-01)
Chen, Jun-Rong
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Ko, Tsung-Shine
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Lu, Tien-Chang
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Chang, Yi-An
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Kuo, Hao-Chung
InGaP/AIGaInP 660-nm resonant-cavity light-emitting diodes (RCLEDs) with stable temperature characteristics have been achieved by extending the resonant cavity length from one optical wavelength (1 lambda) to three optical wavelengths (3 lambda) and tripling the number of quantum wells. When the operation temperature increases from 25 degrees C to 95 degrees C, the degree of power variation at 20 mA is reduced from -2.1 dB to -0.6 dB for the conventional 1-lambda cavity RCLEDs and 3-lambda cavity RCLEDs, respectively. In order to interpret the temperature-dependent experimental results, advanced device simulation is applied to model the RCLEDs with different cavity designs. According to the numerical simulation results, we deduce that the stable temperature-dependent output performance should originate from the reduction of electron leakage current and thermally enhanced hole transport for the 3-lambda cavity AIGaInP RCLEDs.
Hole injection and electron overflow improvement in InGaN/GaN light-emitting diodes by a tapered AlGaN electron blocking layer
(2014-01-13)
Lin, Bing-Cheng
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Chen, Kuo-Ju
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Wang, Chao-Hsun
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Chiu, Ching-Hsueh
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Lan, Yu-Pin
A tapered AlGaN electron blocking layer with step-graded aluminum composition is analyzed in nitride-based blue light-emitting diode (LED) numerically and experimentally. The energy band diagrams, electrostatic fields, carrier concentration, electron current density profiles, and hole transmitting probability are investigated. The simulation results demonstrated that such tapered structure can effectively enhance the hole injection efficiency as well as the electron confinement. Consequently, the LED with a tapered EBL grown by metal-organic chemical vapor deposition exhibits reduced efficiency droop behavior of 29% as compared with 44% for original LED, which reflects the improvement in hole injection and electron overflow in our design. (C)2014 Optical Society of America
Improvement in output power of a 460 nm InGaN light-emitting diode using staggered quantum well
(2010-09-15)
Liao, Chih-Teng
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Tsai, Miao-Chan
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Liou, Bo-Ting
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Yen, Sheng-Horng
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Kuo, Yen-Kuang
Staggered quantum well structures are studied to eliminate the influence of polarization-induced electrostatic field upon the optical performance of blue InGaN light-emitting diodes (LEDs). Blue InGaN LEDs with various staggered quantum wells which vary in their indium compositions and quantum well width are theoretically studied and compared by using the APSYS simulation program. According to the simulation results, the best optical characteristic is obtained when the staggered quantum well is designed as In(0.20)Ga(0.80)N (1.4 nm)-In(0.26)Ga(0.74)N (1.6 nm) for blue LEDs. Superiority of this novelty design is on the strength of its enhanced overlap of electron and hole wave functions, uniform distribution of holes, and suppressed electron leakage in the LED device. (C) 2010 American Institute of Physics. [doi:10.1063/1.3471804]
Numerical analysis on the effect of electron blocking layer in 365-nm ultraviolet light-emitting diodes
(2015-01-01)
Chen, Fang-Ming
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Chang, Jih-Yuan
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Kuo, Yen-Kuang
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Lin, Bing-Cheng
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Kuo, Hao-Chung
For 365-nm ultraviolet light-emitting diodes (UV LEDs), an electron blocking layer (EBL) is usually utilized to mitigate electron overflow. However, using EBL might obstruct holes from injecting into the active region. Moreover, the large polarization field in conventional EBL might also pull down the effective barrier height for electrons, and thus the electrons could easily overflow to the p-side region. To solve the above drawbacks, in this study, the Al content and p-doping concentration of the EBL in typical 365-nm UV LEDs are investigated systematically. Specifically, designs of AlGaN/GaN superlattice EBL and Al-content-graded EBL are explored in detail.
Numerical Study of (0001) Face GaN/InGaN p-i-n Solar Cell With Compositional Grading Configuration
(2012-06-15)
Kuo, Yen-Kuang
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Lin, Bing-Cheng
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Chang, Jih-Yuan
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Chen, Fang-Ming
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Kuo, Hao-Chung
The advantages of a (0001) face GaN/InGaN p-i-n solar cell with compositional grading configuration between i-InGaN/p-GaN layers are studied numerically. With the use of the grading layer, the conversion efficiency is markedly promoted due to the reduction of potential barrier height for holes and due to the decrease of polarization. Optimized conversion efficiency is obtained when the thickness of the grading layer increases to a critical value. This critical thickness is strongly influenced by the polarization charges and doping concentration of the grading layer. When the density of the polarization charges is high or the doping concentration is low, a thick grading layer is required to achieve high efficiency.
Numerical Study on Optimization of Active Layer Structures for GaN/AlGaN Multiple-Quantum-Well Laser Diodes
(2008-09-01)
Chen, Jun-Rong
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Ko, Tsung-Shine
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Su, Po-Yuan
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Lu, Tien-Chang
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Kuo, Hao-Chung
Theoretical analysis for different active layer structures is performed to minimize the laser threshold current of the ultraviolet GaN/AlGaN multiple-quantum-well laser diodes by using advanced device simulation. The simulation results show that the lower threshold current can be obtained when the number of quantum wells is two or three and the aluminum composition in the barrier layer is about 10%-12%. This result is attributed to several different effects including electron leakage current, nonuniform carrier distribution, interface charge density induced by spontaneous and piezoelectric polarization, and optical confinement factor. These internal physical mechanisms are investigated by theoretical calculation to analyze the effects of quantum-well number and different aluminum compositions in barrier layer on laser threshold properties. Furthermore, the effect of quantum-well thickness is discussed as well. It is found that the optimal quantum-well thickness is about 3 nm due to the balance of the advantages of a large confinement factor against the disadvantages of significant quantum-confined Stark effect (QCSE).
Numerical study on optimization of InGaN multi-quantum-well laser diodes with polarization-matched AlInGaN barrier layers
(2009)
Chen, Jun-Rong
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Ko, Tsung-Shine
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Su, Po-Yuan
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Lu, Tien-Chang
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Kuo, Hao-Chung
The optical properties of InGaN multi-quantum-well laser diodes with different polarization-matched AlInGaN barrier layers have been investigated numerically by employing an advanced device simulation program. The use of quaternary polarization-matched AlInGaN barrier layers enhances the electron-hole wave function overlap due to the compensation of polarization charges between InGaN quantum well and AlInGaN barrier layer. According to the simulation results, it is found that among the polarization-matched quantum-well structures under study, lower threshold current and higher slope efficiency can be achieved simultaneously when the aluminum composition in AlInGaN barrier layers is about 10 similar to 15%. The optimal polarization-matched InGaN/AlInGaN laser diode shows lower threshold current and higher slope efficiency compared to conventional InGaN/InGaN laser diodes.
Simulation and Experimental Study on Barrier Thickness of Superlattice Electron Blocking Layer in Near-Ultraviolet Light-Emitting Diodes
(2016-08-01)
Kuo, Yen-Kuang
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Chen, Fang-Ming
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Lin, Bing-Cheng
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Chang, Jih-Yuan
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Shih, Ya-Hsuan
The optical performance and relevant physical properties of near-ultraviolet (NUV) GaN-based light-emitting diodes (LEDs) are investigated. Specifically, the influence of traditional AlGaN bulk electron blocking layer (EBL) and AlGaN/GaN superlattice (SL) EBL with various thicknesses of AlGaN layers on NUV LEDs is explored. It is indicated from the band diagrams, electrostatic field profile, electron reflecting and hole transmitting spectra, and carrier concentrations profile that the use of a thin AlGaN layer of AlGaN/GaN SL EBL is beneficial to the electron confinement and hole injection in the active region, which results in the high internal quantum efficiency and low efficiency droop at high injection current. Moreover, the experimental results show that replacing the traditional AlGaN bulk EBL with the AlGaN/GaN SL EBL can markedly improve the optical performance. When compared with the NUV LED with traditional AlGaN bulk EBL, the output power of the NUV LED with the proposed AlGaN/GaN SL EBL increases from 13.5 to 48.7 mW at 100 mA.
The carrier blocking effect on 850 nm InAlGaAs/AlGaAs vertical-cavity surface-emitting lasers
(2006-10-01)
Chang, Yi-An
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Ko, Tsung-Shine
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Chen, Jun-Rong
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Lai, Fang-I
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Yu, Chun-Lung
In this study, the carrier blocking effect on 850 nm InAlGaAs/AlGaAs vertical-cavity surface-emitting layers (VCSELs) was theoretically and experimentally investigated. By means of inserting a high-bandgap electron blocking layer, which was either 10 nm thick Al0.75Ga0.25As or 13 nm thick Al0.9Ga0.1As, on the p-side of a quantum-well active region, the laser output performance was theoretically found to be improved. VCSELs with and without an electron blocking layer were also experimentally demonstrated. It was found that the threshold current was reduced from 1.47 to 1.33 mA and the slope efficiency was increased from 0.37 to 0.53 mW mA(-1) by inserting a 10 nm thick Al0.75Ga0.25As electron blocking layer. Also, the device became less sensitive to the device temperature, where the amount of increase in the threshold current at an elevated temperature of 95 degrees C was only 0.27 mA and the slope efficiency dropped by only 24.5%. A peak frequency response of nearly 9 GHz at 5 mA, measured from relative intensity noise (RIN), was obtained in these VCSEL devices.
Theoretical and experimental analysis of temperature-insensitive 655-nm resonant-cavity LEDs
(2007)
Chen, Jun-Rong
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Chang, Yi-An
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Kuo, Hao-Chung
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Lu, Tien-Chang
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Kuo, Yen-Kuang
Visible InGaP/InGaAlP resonant-cavity light-emitting diodes with low temperature sensitivity output characteristics were demonstrated. By means of extending the resonant cavity to a thickness of three wavelength (3 lambda), the degree of power variation between 25 and 95 degrees C for the devices biased at 20 mA was apparently reduced from -2.1 dB for the standard structure design (1-lambda cavity) to -0.6 dB. Numerical simulation showed that the insensitive temperature dependence of output characteristics was attributed to the reduced electron leakage current.