Browsing by Author "Shih, Min-Hsiung"

Now showing 1 - 20 of 69

Advantages of Blue LEDs With Graded-Composition AlGaN/GaN Superlattice EBL
(2013-11-01)
Lin, Bing-Cheng
;
Chen, Kuo-Ju
;
Han, Hau-Vei
;
Lan, Yu-Pin
;
Chiu, Ching-Hsueh
InGaN/GaN light-emitting diodes (LEDs) with graded-composition AlGaN/GaN superlattice (SL) electron blocking layer (EBL) were designed and grown by metal-organic chemical vapor deposition. The simulation results demonstrated that the LED with a graded-composition AlGaN/GaN SL EBL have superior hole injection efficiency and lower electron leakage over the LED with a conventional AlGaN EBL or normal AlGaN/GaN SL EBL. Therefore, the efficiency droop can be alleviated to be similar to 20% from maximum at an injection current of 15-120 mA, which is smaller than that for conventional AlGaN EBL (30%). The corresponding experimental results also confirm that the use of a graded-composition AlGaN/GaN SL EBL can markedly enhance the light output power by 60%.
An Investigation of the Optical Analysis in White Light-Emitting Diodes With Conformal and Remote Phosphor Structure
(2013-11-01)
Chen, Kuo-Ju
;
Chen, Hsin-Chu
;
Lin, Chien-Chung
;
Wang, Chao-Hsun
;
Yeh, Chia-Chi
An effective emission model of phosphor film is proposed by using bidirectional scattering distribution function system (BSDF), and the model is verified by white light-emitting diodes (LEDs) with conformal and remote phosphor structure. The emission model is built to clarify the optical characteristics by analyzing the angular-dependent distribution of emission and excitation behaviors in phosphor film. The white LEDs with conformal and remote phosphor structure are also fabricated for experimental comparison. The uniformity of angular correlated color temperature (CCT) in white LEDs can be determined by the angular distribution of blue and yellow light, which is in turns decided by the refractive index variation between chip a (c) nd phosphor layers. Finally, the experimental results are found to have good agreement with the simulation results performing by the Monte Carlo method.
Catalytically solid-phase self-organization of nanoporous SnS with optical depolarizability
(2016)
Cheng, Chih-Hsien
;
Chi, Yu-Chieh
;
Wu, Chung-Lun
;
Lin, Chun-Jung
;
Tsai, Ling-Hsuan
The catalytic solid-phase synthesis of self-organized nanoporous tin sulfide (SnS) with enhanced absorption, manipulative transmittance and depolarization features is demonstrated. Using an ultralow radio-frequency (RF) sputtering power, the variation of the orientation angle between the anodized aluminum oxide (AAO) membrane and the axis of the sputtered ion beam detunes the catalytically synthesized SnS from nanorod to nanoporous morphology, along the sidewall of the AAO membrane. The ultraslow catalytic sputtering synthesis on the AAO at the RF plasma power of 20 W and the orientation angle of 0 degrees regulates the porosity and integrality of nanoporous SnS, with average pore diameter of 80-150 nm. When transferring from planar to nanoporous structure, the phase composition changes from SnS to SnS2-Sn2S3, and the optical bandgap shrinks from 1.43 to 1.16 eV, due to the preferred crystalline orientation, which also contributes to an ultralow reflectance of <1% at 200-500 nm when both the transmittance and the surface scattering remain at their maxima. The absorption coefficient is enhanced by nearly one order of magnitude with its minimum of >5 x 10(4) cm(-1) at the wavelength between 200 and 700 nm, due to the red-shifting of the absorption spectrum to at least 100 nm. The catalytically self-organized nanoporous SnS causes strong haze and beam divergence of 20 degrees-30 degrees by depolarized nonlinear scattering at the surface, which favors the solar energy conversion with reduced surface reflection and enhanced photon scattering under preserved transmittance.
Circular Dichroism Control of Tungsten Diselenide (WSe2) Atomic Layers with Plasmonic Metamolecules
(2018-05-09)
Lin, Hsiang-Ting
;
Chang, Chiao-Yun
;
Cheng, Pi-Ju
;
Li, Ming-Yang
;
Cheng, Chia-Chin
Controlling circularly polarized (CP) states of light is critical to the development of functional devices for key and emerging applications such as display technology and quantum communication, and the compact circular polarization-tunable photon source is one critical element to realize the applications in the chip-scale integrated system. The atomic layers of transition metal dichalcogenides (TMDCs) exhibit intrinsic CP emissions and are potential chiroptical materials for ultrathin CP photon sources. In this work, we demonstrated CP photon sources of TMDCs with device thicknesses approximately 50 nm. CP photoluminescence from the atomic layers of tungsten diselenide (WSe2) was precisely controlled with chiral metamolecules (MMs), and the optical chirality of WSe2 was enhanced more than 4 times by integrating with the MMs. Both the enhanced and reversed circular dichroisms had been achieved. Through integrations of the novel gain material and plasmonic structure which are both low-dimensional, a compact device capable of efficiently manipulating emissions of CP photon was realized. These ultrathin devices are suitable for important applications such as the optical information technology and chip-scale biosensing.
Circular Polarized Emission of Tungsten Diselenide (WSe2) Atomic Layers with Plasmonic Metasurface
(2018-01-01)
Lin, Hsiang-Ting
;
Chang, Chiao-Yun
;
Cheng, Pi-Ju
;
Li, Ming-Yang
;
Cheng, Chia-Chin
A circularly polarized light source with ultrathin geometry were demonstrated by integrating the WSe2 atomic layers with plasmonic chiral metasurfaces. The intrinsic chiral emission of WSe2 was manipulated by chiral metasurfaces to achieve emission circular dichroism more than 25%.
Circular Polarized Lasing Characteristics in Metal/GaN Double-Spiral Nanowire Cavity
(2017-01-01)
Yu, Cheng-Li
;
Liao, Shu-Wei
;
Hsiao, Yu-Hao
;
Kuo, Hao-Chung
;
Shih, Min-Hsiung
Room temperature highly circular polarized laser was demonstrated with a compact metal/GaN double-spiral nanowire cavity. The lasing action was observed with a UV wavelength of 363 nm and a high dissymmetry factor of +1.05.
Circularly-polarized lasing of ultraviolet plasmonic gammadion nanocavity
(2019-01-01)
Cheng, Pi-Ju
;
Lai, Ming-Sheng
;
Hsiao, Yu-Hao
;
Yu, Cheng-Li
;
Chang, Chiao-Yun
In this work, we present the model of plasmonic chrial nanolasers composed of aluminum-coated gallium-nitride (GaN) gammadions, which may lase with a high degree of circular polarization at room temperatures. Using the finite-element method, we examine resonant modes of the four-fold rotationally symmetric cavities of gammadions whose resonant frequencies lie in the gain spectrum of GaN. We find a degenerate doublet of resonant modes which can couple to plane waves in the far-field zone above gammadions. Their near-field profiles exhibit localized distribution in the arms of gammadions and a Fabry-Perot standing-wave pattern along the post. In practice, fabrication imperfections would inevitably spoil the four-fold rotation symmetry of gammadions. Typical perturbation could lift the degeneracy of doublet and leads to mixing of the two degenerate modes which may still output signals with observable handedness above gammadions. Considering a gammadion cavity with a single elongated arm, we show that the magnitude of dissymmetry factor of its resonant mode can be larger than unity. Our calculations are consistent with the experimental results, indicating that the right-handed gammadion cavities lase with a magnitude of dissymmetry factors near 1 at a wavelength of 364 nm. The dimensionless effective mode volume scaled by the cube of effective wavelength is 2.62, reflecting a modal distribution remarkably confined in the plasmonic structures and the capability of enhancing the spontaneous-emission rate noticeably. These chiral nanolasers with an ultrasmall footprint could be potentially utilized as future circularly-polarized photon source at the chip level.
Compact Tunable Laser With InGaAsP Photonic Crystal Nanorods for C-Band Communication
(2015-11-01)
Shih, Min-Hsiung
;
Hsu, Kung-Shu
;
Lee, Kevin
;
Lai, Kun-Ting
;
Lin, Chun-Ting
In this study, an ultracompact tunable laser with InGaAsP photonic crystal nanorods for optical communication was demonstrated within 10-mu m footprint. The square photonic crystal nanorods with the InGaAsP quantum wells were fabricated and embedded in a flexible polydimethylsiloxane substrate. The high-quality single mode lasing with low threshold around the symmetry point Gamma was achieved in experiments. The lasing wavelength can be linearly fine-tuned by varying the extension percentage of photonic crystals and the wavelength tunable range covers the whole conventional band communication ambit. The lasing wavelength shift is attributed to the PhC lattice distortion, and its tuning behavior agrees with the 3-D simulation results. This ultrasmall, wide-range wavelength tunable laser can function as a novel light source for the chip-scale photonic integrated circuits and optics communication system.
Defect Mode Lasing in metal-coated GaN Grating Structure at Room Temperature
(2014)
Chen, Kuo-Ju
;
Hsu, Wan-Hai
;
Liao, Wei-Chun
;
Shih, Min-Hsiung
;
Kuo, Hao-Chung
The lasing action from a metal-coated GaN with defect grating structure was observed and the wavelength is approximately 365 nm with the quality factor of 480 at room temperature.
Efficiency and Droop Improvement in GaN-Based High-Voltage Flip Chip LEDs
(2014-01-01)
Chiang, Yen-Chih
;
Lin, Bing-Cheng
;
Chen, Kuo-Ju
;
Chiu, Sheng-Huan
;
Lin, Chien-Chung
The GaN-based high-voltage flip chip light-emitting diode (HVFC-LED) is designed and developed for the purpose of efficiency enhancement. In our design, the distributed Bragg reflector (DBR) is deposited at the bonded substrate to increase the light extraction. After the flip chip process, the general current-voltage characteristics between the flip chip sample and the traditional sample are essentially the same. With the help of great thermal conductive silicon substrate and the bottom DBR, the HVFC-LED is able to enhance the power by 37.1% when compared to the traditional high-voltage LEDs. The wall-plug efficiencies of the HVFC-LED also show good droop reduction as high as 9.9% compared to the traditional devices.
Efficiency and Droop Improvement in GaN-Based High-Voltage Flip Chip LEDs
(2014-01-01)
Chiang, Yen-Chih
;
Lin, Bing-Cheng
;
Chen, Kuo-Ju
;
Chiu, Sheng-Huan
;
Lin, Chien-Chung
The GaN-based high-voltage flip chip light-emitting diode (HVFC-LED) is designed and developed for the purpose of efficiency enhancement. In our design, the distributed Bragg reflector (DBR) is deposited at the bonded substrate to increase the light extraction. After the flip chip process, the general current-voltage characteristics between the flip chip sample and the traditional sample are essentially the same. With the help of great thermal conductive silicon substrate and the bottom DBR, the HVFC-LED is able to enhance the power by 37.1% when compared to the traditional high-voltage LEDs. The wall-plug efficiencies of the HVFC-LED also show good droop reduction as high as 9.9% compared to the traditional devices.
Efficiency and Droop Improvement in Hybrid Warm White LEDs Using InGaN and AlGaInP High-Voltage LEDs
(2013-04-01)
Chen, Kuo-Ju
;
Kuo, Hsuan-Ting
;
Chiang, Yen-Chih
;
Chen, Hsin-Chu
;
Wang, Chao-Hsun
This study investigates the optical and electrical characteristics in hybrid warm white high-voltage light-emitting diodes (HV-LEDs). The luminous efficiency of the hybrid warm white LED in this study improved by 11% and 51%, compared to conventional cool and warm LEDs, respectively, solving the warm white gap in white LEDs. The efficiency droop of the hybrid warm white LED was reduced to 21.8% from 26.8% for the conventional cool white LED, and from 26.3% in the conventional warm white LED at 40 mA (35 A/cm(2)) the operated current. Furthermore, the color rendering index (CRI) and angular correlated color temperature (CCT) were analyzed, indicating a significant improvement in hybrid warm white HV-LEDs.
Efficient Heat Dissipation of Photonic Crystal Microcavity by Mono layer Graphene
(2013-12-01)
Shih, Min-Hsiung
;
Li, Lain-Jong
;
Yang, Yi-Chun
;
Chou, Hsiang-Yu
;
Lin, Cheng-Te
Graphene, which exhibits excellent thermal conductivity, is a potential heat dissipation medium for compact optoelectronic devices. Photonic devices normally produce large-quantity of unwanted heat, and thus, a heat dissipation strategy is urgently needed. In this study, single-layer graphene (SLG) grown by chemical vapor deposition (CVD) is used to cover the surface of a photonic crystal (PhC) cavity, where the heat flux produced by the PhC cavity can be efficiently dissipated along the in-plane direction of the SLG. The thermal properties of the graphene-capped PhC cavity were characterized by experiments and theoretical calculations. The thermal resistance of the SLG-capped PhC cavity obtained from experiments is lower than half of that of a bare PhC cavity. The temperature of a SLG-capped PhC cavity is 45 K lower than that without SLG capping under an optical power of 100 mu W. Our simulation results indicate that SLG receives the majority of the heat fluxes from the device, leading to the efficient heat dissipation. Both the experimental and simulation results suggest that the SLG is a promising material to enhance the heat dissipation efficiency for optoelectronic applications.
Efficient hybrid white light-emitting diodes by organic-inorganic materials at different CCT from 3000K to 9000K
(2015-04-06)
Chen, Kuo-Ju
;
Lai, Yi-Chun
;
Lin, Bin-Cheng
;
Lin, Chien-Chung
;
Chiu, Sheng-Huan
The hybrid white light-emitting didoes (LED) with polyfluoren (PFO) polymer and quantum dot (QD) was investigated using dispensing method at the different correlated color temperature (CCT) for cool and warm color temperature. This result indicates that the hybrid white LED device has the higher luminous efficiency than the convention one, which could be attributed to the increased utilization rate of the UV light. Furthermore, the CIE 1931 coordinate of high quality white hybrid LED with different CCT range from 3000K to 9000K is demonstrated. Consequently, the angular-dependent CCT and the thermal issue of the hybrid white LED device were also analyzed in this study. (C) 2015 Optical Society of America
Efficient wavelength conversion with low operation power in a Ta2O5-based micro-ring resonator
(2017-12-01)
Wu, Chung-Lun
;
Huang, Jen-Yang
;
Ou, Ding-Hsin
;
Liao, Ting-Wei
;
Chiu, Yi-Jen
The Ta2O5-based micro-ring resonator with an unloaded quality factor of 182,000 has been demonstrated to realize efficient nonlinear wavelength generation. The propagation loss of the resonator is 0.5 cm(-1), and the buildup factor of the ring resonator is estimated to be similar to 50. With a high buildup factor of the ring structure, the four-wave-mixing (FWM) conversion efficiency of -30 dB is achieved in the resonator with a pump power of 6 mW. Based on power-dependent FWM results, the nonlinear refractive index of Ta2O5 is estimated to be 1.4x10-14 cm(2)/W at a wavelength of similar to 1550 nm. The demonstration of an enhanced FWM process in the Ta(2)O(5-)based micro-ring cavity implies the possibility of realizing FWM-based optical parametric oscillation in a Ta2O5-based micro-ring resonator. (C) 2017 Optical Society of America
Enhanced Luminous Efficiency of WLEDs Using a Dual-Layer Structure of the Remote Phosphor Package
(2013-06-15)
Chen, Kuo-Ju
;
Chen, Hsin-Chu
;
Shih, Min-Hsiung
;
Wang, Chao-Hsun
;
Tsai, Hsin-Han
This study demonstrates how the insertion of a thin silicone layer into a dual-layer remote phosphor structure enhances light extraction in white light-emitting diodes (WLEDs). In the experiment, a dual-layer phosphor structure yielded a higher intensity of blue and yellow components than a conventional structure. Moreover, the lumen flux was 5% higher than a conventional remote phosphor package at the same correlated color temperature (CCT). Using a TFCalc32 simulation, the electric field intensity was calculated for different thicknesses of the dual-layer remote phosphor structures, and the enhanced use of blue rays was verified. Additionally, the dual-layer structure reduces chromaticity deviations as the driving current increases.
Enhancement of angular CCT by hybrid phosphor structure in White Light-emitting Diodes
(2013)
Chen, Kuo-Ju
;
Chen, Hsin-Chu
;
Shih, Min-Hsiung
;
Wang, Chao Hsun
;
Chien, Shih-Hsuan
The hybrid phosphor structure for white light-emitting diodes application was reported. It was demonstrated that the improvement of the luminous efficiency as well as the good uniform angular correlated color temperature (CCT) in hybrid phosphor structure compared with the conventional dispense method. The experimental results showed the CCT deviation was improved from 453K to 280K in the range of -70 to 70 degrees, which could be attributed to the large divergent angle of blue light. Moreover, the high lumen output was also achieved, as compared with dispense and conformal phosphor structures. Therefore, the experimental results indicated that the hybrid phosphor structure was feasible to use in the solid state lighting.
Enhancement of power conversion efficiency in GaAs solar cells with dual-layer quantum dots using flexible PDMS film
(2012-09-01)
Chen, Hsin-Chu
;
Lin, Chien-Chung
;
Han, Hau-Vei
;
Chen, Kuo-Ju
;
Tsai, Yu-Lin
"This study demonstrates the high performance of GaAs solar cells with dual-layer CdS quantum dots (QDs) carried by flexible polydimethylsiloxane (PDMS) film. Several parameters were enhanced, including the short circuit current, fill factor, and power conversion efficiency, which were measured under white light illumination similar to the solar spectrum. The flexible PDMS film was fabricated using the spin-coating technique, and was then used to embed dual-layer CdS QDs. Different concentrations of QDs were applied in this design to test the optimal combination. The proposed scheme enhances power conversion efficiency by 22%, compared to a GaAs solar cell without CdS QDs. The photon down-conversion capability in the ultraviolet (UV) range and additional antireflection capability in the longer visible-IR range were verified through the external quantum efficiency. (C) 2012 Elsevier B.V. All rights reserved."
Excellent Color Quality of White-Light-Emitting Diodes by Embedding Quantum Dots in Polymers Material
(2016-01-01)
Lin, Huang-Yu
;
Wang, Sheng-Wen
;
Lin, Chien-Chung
;
Chen, Kuo-Ju
;
Han, Hau-Vei
This study employs the polyfluorene composite (called Green B) with several colors of quantum dots to generate the high-color-rendering index (CRI) white LEDs. The Green B polymer is a good candidate to manufacture the hybrid w-LED because of its good quantum efficacy. The hybrid w-LEDs are fabricated by the mixing of Green B with yellow quantum dots and red quantum dots or orange quantum dots to obtain the correlated color temperatures of 3500 and 5500 K. The use of the hybrid polymer/QDs w-LEDs is proved to be beneficial as QD w-LEDs can improve the CRI up to 90 in 3500 K. The luminous efficiency of such devices can be as high as 17.2l m/W.
Flexible Localized Surface Plasmon Resonance Sensor with Metal-Insulator-Metal Nanodisks on PDMS Substrate
(2018-08-07)
Chang, Chiao-Yun
;
Lin, Hsiang-Ting
;
Lai, Ming-Sheng
;
Shieh, Teng-Yi
;
Peng, Chien-Chung
The small sized, flexible, high-performed and bio-compatible sensing devices are the critical elements to realize the bio-related detection or on-site health monitoring systems. In this work, the flexible localized surface plasmon resonance (LSPR) bio-sensors were demonstrated by integrating the metal-insulator-metal (MIM) nanodisks with bio-compatible polydimethylsiloxane (PDMS) substrate. The different geometries of MIM nanodisk sensors were investigated and optimized to enhance the spatial overlap of the LSPR waves with the environment, which lead to a high sensitivity of 1500 nm/RIU. The omni-directional characteristics of LSPR resonances were beneficial for maintaining the device sensitivity stable under various bending curvatures. Furthermore, the flexible MIM nanodisk LSPR sensor was applied to detect A549 cancer cells in PBS+ solution. The absorption peak of the MIM-disk LSPR sensor obviously redshift to easily distinguish between the phosphate buffered saline (PBS+) solution with A549 cancer cells and without cells. Therefore, the flexible MIM nanodisk LSPR sensor is suitable to develop on-chip microfluidic biosensors for detection of cancer cells on nonplanar surfaces.