Browsing by Author "Yeh, Wen-Yung"

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Anisotropy of light extraction from GaN two-dimensional photonic crystals
(2008-05-12)
Lai, Chun-Feng
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Chi, Jim-Yong
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Kuo, Hao-Chung
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Chao, Chia-Hsin
;
Hsueh, Han-Tsung
Angular distribution of light diffracted out of the plane of two-dimensional photonic crystals ( PhC) has been studied in the azimuthal direction with a specially designed waveguide structure. The optical images of the light extraction patterns from the guided photoluminescence light are obtained with laser excitation in the center of the annual structure made on GaN multilayer. For increasing lattice constant, symmetric patterns with varying number of petals according to the symmetry of the PhC are observed. The appearance and disappearance of the petals can be explained using the Ewald construction in the reciprocal space. The dependence of light extraction on the lattice constant and orientation, and incident angle are investigated. (C) 2008 Optical Society of America.
Characteristics of Single-Chip GaN-Based Alternating Current Light-Emitting Diode
(2008-12-01)
Yen, Hsi-Hsuan
;
Kuo, Hao-Chung
;
Yeh, Wen-Yung
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光電工程學系
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Department of Photonics
In this study, a GaN-based alternating current light-emitting diode (AC-LED) with 34 numbers of microchips illuminated in each bias direction was fabricated. After calibrating the integration duration, the light output powers of the AC-LED driven by AC and DC were 388.1 and 312.8 mW when the input power was about I W, respectively. The flickering illumination mode of the AC-LED driven by AC decreased the heat accumulation and revealed a higher energy utilization efficiency than that of the AC-LED driven by DC. The larger blue shift and smaller full width at half maximum of the AC-LED driven by AC than those of the AC-LED driven by DC were also observed. [DOI: 10.1143/JJAP.47.8808]
Directional light extraction enhancement from GaN-based film-transferred photonic crystal light-emitting diodes
(2009-03-23)
Lai, Chun-Feng
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Chao, Chia-Hsin
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Kuo, Hao-Chung
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Yen, His-Hsuan
;
Lee, Chia-En
Experimental investigation of the directionality in the far-field pattern and light extraction enhancement in collected cone were performed in GaN-based film-transferred photonic crystal (PhC) light-emitting diodes (FTLEDs). Angular-resolved measurement revealed directional profile and azimuthal anisotropy in the far-field distribution with guided modes extraction. Good agreement according to Bragg's diffraction theory and free photon band structure were achieved. The light enhancement in PhC FTLEDs compared to non-PhC FTLEDs within the collection cone angle was obtained according to measured three-dimensional far-field patterns. In a +/- 20 degrees collection cone, collected light was enhanced by a factor of similar to 2.4 for the collimated PhC FTLED.
Directional Light Extraction from Photonic Crystal Thin-film GaN Light-Emitting Diodes
(2009-01-01)
Chao, Chia-Hsin
;
Lai, Chun-Feng
;
Kuo, Hao-Chung
;
Yeh, Wen-Yung
;
光電工程學系
The light enhancement of PhC LEDs within the collection cone angle was obtained according to measured far-field patterns In a +/- 20 degrees collection cone, the collimated PhC LED was enhanced up to similar to 2.4.
Divergent Far-Field III-Nitride Ultrathin Film-Transferred Photonic Crystal Light-Emitting Diodes
(2010)
Lai, Chun-Feng
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Chao, Chia-Hsin
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Kuo, Hao-Chung
;
Yu, Peichen
;
Yen, His-Hsuan
The divergent far-field distribution of III-nitride ultrathin film-transferred light-emitting diodes (FTLEDs) with ellipse holes of triangular photonic crystal (PhC) lattice have been experimental and theoretical studies. Angular-and-spectral-resolved measurement revealed guided modes extraction behaviors which obtain good agreement with theoretical model according to two-dimensional free photon band structure. The azimuthal evolution of the guided modes' diffraction behavior according to Bragg's diffraction has also been discussed by angular-resolved monochromatical mapping. Finally, the PhC FTLEDs show light enhancement with the divergence far-field pattern that exhibited 130% at a driving current of 200mA as compared with non-PhC (without PhC) FTLEDs. This could lead to promising LEDs with unusual divergent far-field properties for specific applications. (C) 2010 The Japan Society of Applied Physics
Far-Field and Near-Field Distribution of GaN-Based Photonic Crystal LEDs With Guided Mode Extraction
(2009-07-01)
Lai, Chun-Feng
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Chi, Jim-Yong
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Kuo, Hao-Chung
;
Yen, Hsi-Hsuan
;
Lee, Chia-En
The near-field and far-field distribution of GaN LEDs with square photonic crystal (PhC) lattice are experimentally investigated. The optical images of the near-field pattern are obtained from the guided electroluminescent light generated at the center of a special annular structure. For increasing lattice constant, symmetric patterns with varying number of petals according to the symmetry of the PhC are observed. The far-field distribution is studied with GaN-based film-transferred PhC LEDs with the thickness about 1500 nm. Angular-resolved measurements under electrical injection revealed guided modes extraction behavior and polarization based on the Bragg's diffraction with the PhC lattice. Good agreement with the two-dimension free photon band structure is obtained.
Far-field of GaN film-transferred green light-emitting diodes with two-dimensional photonic crystals
(2009-05-25)
Lai, Chun-Feng
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Chi, Jim-Yong
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Kuo, Hao-Chung
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Yen, Hsi-Hsuan
;
Lee, Chia-En
Far-field distributions of GaN-based photonic crystal (PhC) film-transferred light-emitting diodes (FT-LEDs) were investigated. The thickness of the device is about 840 nm. The emission wavelength is around 520 nm. The PhC region is a square lattice with a/lambda around 0.5. Angular-resolved measurements in the Gamma-X and Gamma-M directions were made in the polarized-resolved manner. Guided mode extraction behavior in agreement with the two-dimensional free-photon band calculation was observed. In addition, the pseudo-TM behavior for the non-collinearly coupled modes was observed. The azimuthal-mapping of the angular-resolved spectra revealed the evolution of the collinearly and the non-collinearly coupled modes. Furthermore, the light enhancement of similar to 2.7x and the collimation angle about 102.3 degrees were achieved. (c) 2009 Optical Society of America
GaN alternating current light-emitting device
(2007-06-01)
Yen, Hsi-Hsuan
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Yeh, Wen-Yung
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Kuo, Hao-Chung
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光電工程學系
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Department of Photonics
We report a new design of the light-emitting device which can be operated under alternating current source directly. The new type alternating current driven light-emitting device (AC LED) can increase the radition area in each bias direction to improve the device efficiency by the Wheatstone Bridge (WB) circuit design. WB-AC LEDs with different designs were fabricated and the electrical and optical characteristics were measured. It is found that the efficiency of the WB-AC LED is influenced by the varied area ratio of the rectified microchip to the central one because of the different current density and forward bias of each microchip. Additionally, the relationship between the area ratio of microchips and the wall plug efficiency of the WB-AC LED has also been discussed. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
GaN Thickness Effect on Directional Light Enhancement from GaN-Based Film-Transferred Photonic Crystal Light-Emitting Diodes
(2010)
Lai, Chun-Feng
;
Chao, Chia-Hsin
;
Kuo, Hao-Chung
;
Yu, Peichen
;
Yen, His-Hsuan
Directional light enhancement behavior including collimated far-field patterns sensitively depending on both photonic crystal (PhC) lattice constant and GaN thickness from GaN film-transferred light-emitting diodes (FTLEDs) with a triangular PhC lattice has been experimentally studied. Far-field pattern measurement in the Gamma-M and Gamma-K directions of GaN PhC FTLEDs with various lattice constants and GaN thicknesses revealed different far-field profiles as detemined on the basis of guided mode extraction of Bragg's diffraction. Additionally, three-dimensional (3D) far-field measurement revealing the PhC diffraction patterns was also demonstrated. We also used the 3D finite-different time-domain method to confirm the experimental results. (C) 2010 The Japan Society of Applied Physics
GaN-based film-transferred light-emitting diodes with photonic crystal
(2009)
Lai, Chun-Feng
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Chi, Jim-Yong
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Chao, Chia-Hsin
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Lee, Chia-En
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Kuo, Hao-Chung
Experimental investigation of A-type and B-type guided modes was performed in GaN-based film-transferred photonic crystal light-emitting diodes. Good agreement with the band structure calculated in the limit of two-dimensional free photon was obtained. (C)2009 Optical Society of America
Highly-directional emission patterns based on near single guided mode extraction from GaN-based ultrathin microcavity light-emitting diodes with photonic crystals
(2010-07-05)
Lai, Chun-Feng
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Kuo, Hao-Chung
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Yu, Peichen
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Lu, Tien-Chang
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Chao, Chia-Hsin
This study investigates the distribution of highly-directional far-field emission on GaN-based ultrathin microcavity light-emitting diodes (uMCLEDs) with photonic crystals (PhCs). The ultrathin 550 nm cavity, PhC lattice constant of 370 nm, and hole depth of 250 nm in the GaN PhC uMCLED provide near single guided mode extraction and a pattern of high directionality radiation. Angular-spectral-resolved electroluminescence measurements reveal photon-band structure agreement with the fundamental mode effective refractive index dispersion curve. In addition, GaN PhC uMCLED increase the output power extraction efficiency by 145.9% (similar to 2.46x) compared with GaN non-PhC uMCLED, and a directional far-field emission pattern at half intensity of nearly +/- 15 degrees. (C) 2010 American Institute of Physics. [doi:10.1063/1.3459970]
Light Extraction from Photonic Crystal Ultra-thin GaN Light-Emitting Diodes with ITO Current Spreading Layer
(2009-01-01)
Chao, Chia-Hsin
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Lai, Chun-Feng
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Kuo, Hao-Chung
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Yeh, Wen-Yung
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光電工程學系
The optical effect of ITO current spreading layer on light extraction behavior of photonic crystal ultra-thin-film light-emitting diodes was investigated numerically The slab-type ITO layer with half wavelength thickness behaves completely transparent to optical properties.
Light Extraction from Photonic Crystal Ultra-thin GaN Light-Emitting Diodes with ITO Current Spreading Layer
(2009-01-01)
Chao, Chia-Hsin
;
Lai, Chun-Feng
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Kuo, Hao-Chung
;
Yeh, Wen-Yung
;
光電工程學系
The optical effect of ITO current spreading layer on light extraction behavior of photonic crystal ultra-thin-film light-emitting diodes was investigated numerically. The slab-type ITO layer with half wavelength thickness behaves completely transparent to optical properties
Particular Failure Mechanism of GaN-Based Alternating Current Light-Emitting Diode Induced by GaO(x) Oxidation
(2010-08-01)
Yen, Hsi-Hsuan
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Kuo, Hao-Chung
;
Yeh, Wen-Yung
;
光電工程學系
;
Department of Photonics
This investigation describes the unique failure mechanism of the Wheatstone bridge circuit-type alternating current light-emitting diode (WB AC-LED). The micro-LEDs in WB AC-LED rectifying branches were reverse biased, and therefore, positive charges (holes) accumulated in the n-type GaN layer under the active region and combined with the GaN material and OH(-) ions to generate GaO(x) oxidation grains. The GaO(x) generation speed was fast with high reverse voltage applied to micro-LEDs, and the expansion of GaO(x) dimensions degraded the opto-electrical characteristics and eventually caused failure of the WB AC-LED. The root-mean-square reverse voltage dropped across each micro-LED from -13.1 to -6.7 V with different micro-LEDs array arrangements extended the WB AC-LED life-time from being less than 650 h to more than 1600 h, respectively.
Particular Failure Mechanism of GaN-Based Alternating Current Light-Emitting Diode Induced by GaOx Oxidation
(2010-08-01)
Yen, Hsi-Hsuan
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Kuo, Hao-Chung
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Yeh, Wen-Yung
;
光電工程學系
;
光電工程研究所
This investigation describes the unique failure mechanism of the Wheatstone bridge circuit-type alternating current light-emitting diode (WB AC-LED). The micro-LEDs in WB AC-LED rectifying branches were reverse biased, and therefore, positive charges (holes) accumulated in the n-type GaN layer under the active region and combined with the GaN material and OH- ions to generate GaOx oxidation grains. The GaOx generation speed was fast with high reverse voltage applied to micro-LEDs, and the expansion of GaOx dimensions degraded the opto-electrical characteristics and eventually caused failure of the WB AC-LED. The root-mean-square reverse voltage dropped across each micro-LED from -13.1 to -6.7 V with different micro-LEDs array arrangements extended the WB AC-LED life-time from being less than 650 h to more than 1600 h, respectively.
Polarized light emission from photonic crystal light-emitting diodes
(2008-06-16)
Lai, Chun-Feng
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Chi, Jim-Yong
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Yen, Hsi-Hsuan
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Kuo, Hao-Chung
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Chao, Chia-Hsin
We have experimentally studied polarization characteristics of the two-dimensional photonic crystal (PhC) light-emitting diodes (LEDs) using an annular structure with square lattice and observed a strong polarization dependence of the lattice constant and orientation of the PhC. The extracted light from the GaN PhC LEDs has P/S ratios of 5.5 (similar to 85% polarization light) for light propagating in the Gamma X direction and 2.1 (similar to 68% polarization light) for the Gamma M direction, respectively. Based on the couple mode theory, the dependence of polarization behaviors on different lattice constant and orientation was found to be in good agreement with theoretical discussion.
Structural Effects on Highly Directional Far-Field Emission Patterns of GaN-Based Micro-Cavity Light-Emitting Diodes With Photonic Crystals
(2010-10-01)
Lai, Chun-Feng
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Kuo, Hao-Chung
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Chao, Chia-Hsin
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Yu, Peichen
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Yeh, Wen-Yung
This study theoretically and experimentally investigates the highly directional far-field emission patterns of GaN photonic crystal (PhC) micro-cavity light-emitting diodes (MCLEDs) depending on varying structural parameters. Angular-spectra-resolved electroluminescence measurements reveals the behavior of guided-mode extraction which is significantly affected by the structural parameters of GaN PhC MCLEDs, where the GaN cavity thickness decides the extracted guided mode numbers, PhC lattice constant influences the distribution of far-field emission, and PhC hole depth affects the interaction with guided modes. The proposed GaN ultrathin MCLED (uMCLED) with PhC lattice constant of 420 nm and deep hole depth of 250 nm exhibited a maximum output light extraction efficiency of 248% under one-watt input power compared to GaN non-PhC uMCLED and produced a directional far-field emission pattern at half intensity near +/- 17 degrees. The present results indicate that highly directional light extraction enhancement could contribute to developments of many applications, especially for etendue-limited applications such as pico-projectors.