Browsing by Author "Fang, Yen-Hsiang"

Now showing 1 - 10 of 10

Angular color variation in micron-scale light-emitting diode arrays
(2019-08-05)
Yang, Shu-Mei
;
Wang, Po-Hsun
;
Chao, Chia-Hsin
;
Chu, Chun-Wen
;
Yeh, Yin-Tien
A simulation scheme was developed to explore the light distribution of full-color micron-scale light-emitting diode (LED) arrays. The influences of substrate thickness, patterning, and cutting angle of the substrate on several important features, such as light field pattern, light extraction efficiency, and color variation, were evaluated numerically. An experiment was conducted; the results were consistent with simulation results for a 225 x 125 mu m(2) miniLED and those for an 80 x 80 mu m(2) microLED. Based on the simulation results, the light extraction efficiency of LED devices with a substrate increases by 67.75% over the extraction efficiency of those without a substrate. The light extraction efficiency of LED devices with a substrate increases by 113.55% when an additional patterned design is used on green and blue chips. The calculated large angle Delta u'v' can be as low as 0.015 for miniLED devices. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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
;
電子物理學系
;
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.
High performance ultraviolet micro-LED arrays for fine-pitch micro displays
(2019-01-01)
Tsai, Yi-Lin
;
Huang, Yu-Ming
;
Yang, Shu-Mei
;
Kuo, Wei-Hung
;
Fang, Yen-Hsiang
Highly efficient ultraviolet micro LED arrays are demonstrated. Small devices (5 microns in size) suitable for high resolution (725 ppi) can be produced with low leakage current and good emission spectra stability. A 10 by 10 array is achieved with passive-matrix driving connection.
Improved Color Purity of Monolithic Full Color Micro-LEDs Using Distributed Bragg Reflector and Blue Light Absorption Material
(2020-05-01)
Chu, Shao-Yu
;
Wang, Hung-Yu
;
Lee, Ching-Ting
;
Lee, Hsin-Ying
;
Laing, Kai-Ling
In this study, CdSe/ZnS core-shell quantum dots (QDs) with various dimensions were used as the color conversion materials. QDs with dimensions of 3 nm and 5 nm were excited by gallium nitride (GaN)-based blue micro-light-emitting diodes (micro-LEDs) with a size of 30 mu m x 30 mu m to respectively form the green and red lights. The hybrid Bragg reflector (HBR) with high reflectivity at the regions of the blue, green, and red lights was fabricated on the bottom side of the micro-LEDs to reflect the downward light. This could enhance the intensity of the green and red lights for the green and red QDs/micro-LEDs to 11% and 10%. The distributed Bragg reflector (DBR) was fabricated on the QDs color conversion layers to reflect the non-absorbed blue light that was not absorbed by the QDs, which could increase the probability of the QDs excited by the reflected blue light. The blue light absorption material was deposited on the DBR to absorb the blue light that escaped from the DBR, which could enhance the color purity of the resulting green and red QDs/micro-LEDs to 90.9% and 90.3%, respectively.
Microstructure and recording mechanism of Ge/Au bilayer media for write-once optical disc
(2007-04-09)
Wu, T. H.
;
Kuo, P. C.
;
Fang, Yen-Hsiang
;
Chen, Jung-Po
;
Yen, Po-Fu
The recording mechanism of Ge/Au bilayer and its dynamic tests for write-once blue laser high density DVD (HD DVD) are investigated. It is found that Ge2Au3 phase is nucleated between amorphous Ge and crystalline Au layer after room temperature deposition. Crystallization of Ge/Au interface layer at 170-190 degrees C is induced by the nucleated Ge2Au3 sites at the interface, the bilayer structure is further heated to 200-450 degrees C. After heating above 320 degrees C, crystallized Ge are segregated at the grain boundary. The dynamic test results show that this Ge/Au bilayer films can be applied to 1x-2x HD DVD-R. (c) 2007 American Institute of Physics.
Reduction of Efficiency Droop in InGaN Light-Emitting Diode Grown on Self-Separated Freestanding GaN Substrates
(2011-06-15)
Chao, Chu-Li
;
Xuan, Rong
;
Yen, Hsi-Hsuan
;
Chiu, Ching-Hsueh
;
Fang, Yen-Hsiang
Using a GaN nanorod template in a hydride vapor phase epitaxy (HVPE) system can manufacture a freestanding GaN (FS-GaN) substrate with threading dislocation densities down to similar to 10(7) cm(-2). In this letter, we report InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on this FS-GaN substrate. The defect densities in the homoepitaxially grown LEDs were substantially reduced, leading to improved light emission efficiency. Compared with the LED grown on sapphire, we obtained a lower forward voltage, smaller diode ideality factor, and higher light-output power in the same structure grown on FS-GaN. The external quantum efficiency (EQE) of LEDs grown on FS-GaN were improved especially at high injection current, which brought the efficiency droop phenomenon greatly reduced at high current density.
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]
The photonic properties of micro/mini LED arrays with different substrate thickness
(2020-01-01)
Yang, Shu-Mei
;
Wang, Po-Hsun
;
Chao, Chia-Hsin
;
Chu, Chun-Wen
;
Chen, Yu-Sheng
In this study, we review our progress in micro/mini LED arrays and their numerical simulation in optical fields. The variation in substrate thickness will be included in the calculation and the results can provide detailed insight for the optimization of the micro/mini LED structures.