Browsing by Author "Chang, Chiao-Yun"

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3D structural construction of GaN-based light emitting diode by confocal micro-Raman spectroscopy
(2016-01-01)
Li, Heng
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Chang, Chiao-Yun
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Cheng, Hui-Yu
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Chen, Wei-Liang
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Huang, Yi-Hsin
The key issue for light emission strength of GaN-based LEDs is the high defect density and strain in MQWs causing the electric polarization fields. In this work, we construct 3D confocal microspectroscopy to clarify strain distribution and the relationship between photoluminescence (PL) intensity and pattern sapphire substrate (PSS). From 3D construction of E-2(high) Raman and PL mapping, the dislocation in MQW can be traced to the cone tip of PSS and the difference in E-2(high) Raman mapping between substrate and surface is also measured. The ability to measure strain change in 3D structure nondestructively can be applied to explore many structural problems of GaN-based optoelectronic devices.
Characteristics of Polarized Light Emission in a-Plane GaN-Based Multiple Quantum Wells
(2012-07-01)
Chang, Chiao-Yun
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Huang, Huei-Min
;
Lai, Chih Ming
;
Lu, Tien-Chang
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光電工程學系
In this paper, we investigated polarized light emission properties on a series of a-plane GaN/AlGaN multiple quantum wells grown on r-plane sapphire substrates with various well widths by using the polarization-dependent photoluminescence measurement. To clarify reasons of polarization properties in light emission, we applied the 6 x 6 k.p model to simulate the E-K dispersion relationship and wave functions to obtain optical transitions of different polarized emissions. According to our results, the sub-bands of vertical bar Y>-like states are raised toward the top of the valence sub-band level with increasing the well width. And the optical matrix element of y-polarized light emission will dominate the optical transition, leading to the increase of degree of polarization in the thicker well.
Circular Dichroism Control of Tungsten Diselenide (WSe2) Atomic Layers with Plasmonic Metamolecules
(2018-05-09)
Lin, Hsiang-Ting
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Chang, Chiao-Yun
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Cheng, Pi-Ju
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Li, Ming-Yang
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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
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Chang, Chiao-Yun
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Cheng, Pi-Ju
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Li, Ming-Yang
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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%.
Circularly-polarized lasing of ultraviolet plasmonic gammadion nanocavity
(2019-01-01)
Cheng, Pi-Ju
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Lai, Ming-Sheng
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Hsiao, Yu-Hao
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Yu, Cheng-Li
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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.
Depth-resolved confocal micro-Raman spectroscopy for characterizing GaN-based light emitting diode structures
(2013-11-01)
Chen, Wei-Liang
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Lee, Yu-Yang
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Chang, Chiao-Yun
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Huang, Huei-Min
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Lu, Tien-Chang
In this work, we demonstrate that depth-resolved confocal micro-Raman spectroscopy can be used to characterize the active layer of GaN-based LEDs. By taking the depth compression effect due to refraction index mismatch into account, the axial profiles of Raman peak intensities from the GaN capping layer toward the sapphire substrate can correctly match the LED structural dimension and allow the identification of unique Raman feature originated from the 0.3 mu m thick active layer of the studied LED. The strain variation in different sample depths can also be quantified by measuring the Raman shift of GaN A(1)(LO) and E-2(high) phonon peaks. The capability of identifying the phonon structure of buried LED active layer and depth-resolving the strain distribution of LED structure makes this technique a potential optical and remote tool for in operando investigation of the electronic and structural properties of nitride-based LEDs. (C) 2013 AIP Publishing LLC.
Double superstructures in InGaN/GaN nano-pyramid arrays
(2015-10-01)
Chang, Chiao-Yun
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Li, Heng
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Hong, Kuo-Bin
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Yang, Ya-Yu
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Lai, Wei-Chih
We have fabricated and investigated InGaN/GaN nanopyramid arrays grown on c-plane sapphire by selective area growth technique. The double InGaN/GaN superstructures were formed in one GaN pyramid observed in transmittance emission microscopy. The two growth faces on GaN nanopyramind showed different growth rates, resulted in double superheterostructures of semi-polar facets for InGaN/GaN multiple quantum wells (MQWs) and c-plane InGaN/GaN nano-hetero-disk (NHD) under the nanoscale growth condition. The c-plane InGaN/GaN NHD had high Indium composition due to the pulling effect, exhibiting double wavelength emissions from GaN nanopyramid. And InGaN/GaN MQWs and c-plane InGaN/GaN NHD showed extremely low quantum confinement Stark effect, yielding great light emission efficiency. This result is beneficial for the development of blue, green and white light-emitting diodes. (C) 2015 Elsevier Ltd. All rights reserved.
Enhanced internal quantum efficiency in graphene/InGaN multiple-quantum-well hybrid structures
(2012-08-06)
Huang, Huei-Min
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Chang, Chiao-Yun
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Hsu, Yueh-Shan
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Lu, Tien-Chang
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Lan, Yu-Pin
The enhanced internal quantum efficiency of InGaN/GaN multiple-quantum-wells (MQWs) structure is demonstrated by paving the graphene layers on the MQWs surface. Compared to the conventional MQWs, the internal quantum efficiency of the graphene/InGaN MQWs hybrid structure exhibits a remarkable 2-fold increase. The high charge carrier density in graphene layer is accounted for the enhanced internal quantum efficiency. Moreover, the negligible photoluminescence emission peak shift with increasing the excitation power as well as the decrease of radiative recombination lifetime are attributed to the reduced quantum-confined Stark effect, which correlates to the screening of the polarization field in the c-plane nitride-based quantum well structure. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4745211]
Flexible Localized Surface Plasmon Resonance Sensor with Metal-Insulator-Metal Nanodisks on PDMS Substrate
(2018-08-07)
Chang, Chiao-Yun
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Lin, Hsiang-Ting
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Lai, Ming-Sheng
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Shieh, Teng-Yi
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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.
Growth and Characteristics of a-Plane GaN on ZnO Heterostructure
(2012)
Huang, Huei-Min
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Kuo, Chin-Chia
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Chang, Chiao-Yun
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Lin, Yuan-Ting
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Lu, Tien-Chang
We report on growth and characteristics of a-plane GaN/ZnO/GaN epitaxial structures, which can be applied to various optoelectronic devices. The unique optical transitions intrinsic to heterovalent interfaces were found and analyzed. Clear carrier localization effect in the GaN/ZnO heterointerface is observed from the S-shaped energy shift with increasing temperature in the temperature-dependent photoluminescence measurement. The carrier localization also results in strong luminescent intensity and dominates the emission spectrum at room temperature. In addition, the acceptor level originated from the Zn out-diffusion from the ZnO layer is observed in the low temperature photoluminescence spectra, and its binding energy is estimated to be about 0.311 eV. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.080203jes] All rights reserved.
Growth and Characteristics of a-Plane GaN on ZnO Heterostructure
(2013)
Huang, Huei-Min
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Kuo, Chin-Chi
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Chang, Chiao-Yun
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Lin, Yuan-Ting
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Lu, Tien-Chang
High Circular Polarized Nanolaser with Chiral Gammadion Metal Cavity
(2020-05-12)
Yu, Cheng-Li
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Hsiao, Yu-Hao
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Chang, Chiao-Yun
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Cheng, Pi-Ju
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Lin, Hsiang-Ting
We demonstrate a circularly polarized laser with the metal-gallium-nitride gammadion nanocavities. The ultraviolet lasing signal was observed with the high circular dichroism at room temperature under pulsed optical pump conditions. Without external magnetism which breaks the time-reversal symmetry to favor optical transitions of a chosen handedness, the coherent outputs of these chiral nanolasers show a dissymmetry factor as high as 1.1. The small footprint of these lasers are advantageous for applications related to circularly polarized photons in future integrated systems, in contrast to the bulky setup of linearly-polarized lasers and quarter-wave plates.
High Color Conversion Efficiency on Monolayer WSe2 Using Plasmonic Metasurface
(2019-01-01)
Chen, Cheng-Yuan
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Lin, Chen-An
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Lin, Hsiang-Ting
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Chang, Chiao-Yun
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Kuo, Hao-Chung
The atomic scale thickness transition metal dichalcogenides (TMDCs) material could be a potential role of miniature light emitting devices (LED). The high color conversion efficiency between CdSe quantum dot (QD) and monolayer tungsten diselenide (WSe2) with Ag NDs metasurface could enhance the light emission of WSe2. The emission enhancement presented the color conversion due to its absorption spectrum of Ag ND. It had the most ideal overlap with QDs and WSe2 simultaneously, which boosted all the effects that would happen in color conversion. In the future, utilizing plasmonic metasurface and combing the TMDCs emitting visible red light with the GaN-based LED and green QDs to helpfully achieve white light emitting device. (C) 2019 The Author(s)
High efficiency InGaN/GaN light emitting diodes with asymmetric triangular multiple quantum wells
(2014-03-03)
Chang, Chiao-Yun
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Li, Hen
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Lu, Tien-Chang
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光電工程學系
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Department of Photonics
In this study, we demonstrated high efficiency InGaN/GaN light emitting diodes (LEDs) with asymmetric triangular multiple quantum wells (MQWs). Asymmetric triangular MQWs not only contribute to uniform carrier distribution in InGaN/GaN MQWs but also yield a low Auger recombination rate. In addition, asymmetric triangular MQWs with gallium face-oriented inclination band profiles can be immune from the polarization charge originating from typical c-plane InGaN/GaN quantum well structures. In the experiment, LEDs incorporated with asymmetric triangular MQWs with gallium face-oriented inclination band profiles exhibited a 60.0% external quantum efficiency at 20mA and a 27.0% efficiency droop at 100mA (corresponding to a current density of 69A/cm(2)), which accounted for an 11.7% efficiency improvement and a 31.1% droop reduction compared with symmetric square quantum well structure LEDs. (C) 2014 AIP Publishing LLC.
Hybrid Composites of Quantum Dots, Monolayer WSe2, and Ag Nanodisks for White Light-Emitting Diodes
(2020-07-24)
Chang, Chiao-Yun
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Yu, Cheng-Li
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Lin, Chen-An
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Lin, Hsiang-Ting
;
Lee, Andrew Boyi
We investigated hybrid zero-dimensional core-shell CdSe/ZnS quantum dot (QD)/two-dimensional monolayer WSe2 semiconductors with an Ag nanodisk (ND) for manipulating plasmonic-enhanced photoluminescence (PL) and color conversion efficiency. The absorption spectrum of the local surface plasmon resonance (LSPR) effectively overlaps with that of QDs or monolayer WSe2 to considerably enhance PL. The broad absorption spectrum of the LSPR simultaneously overlapped with the emission spectrum of QDs and the absorption spectrum of excitons in WSe2 to enhance the color conversion efficiency. The highest efficiency of color conversion from QDs to WSe2 with Ag ND was 53%. In the future, hybrid QD/transition metal dichalcogenide light emitters could be further integrated with GaN-based white light-emitting diodes to manipulate the color temperature and expand the color gamut to develop a miniature white light-emitting diode.
Investigation of Emission Polarization and Strain in InGaN-GaN Multiple Quantum Wells on Nanorod Epitaxially Lateral Overgrowth Templates
(2011-09-15)
Huang, Huei-Min
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Lu, Tien-Chang
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Chang, Chiao-Yun
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Ling, Shih-Chun
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Chan, Wei-Wen
Non-polar (a-plane) InGaN-GaN multiple quantum wells (MQWs) on the GaN nanorod epitaxially lateral overgrowth templates with different nanorod height have been fabricated. The average in-plane strain in the InGaN MQWs has been determined from 2.73 x 10(-2) to 2.58 x 10(-2) while the nanorod height in templates increases from 0 to 1.7 mu m. The polarization ratio of the emission from InGaN MQWs varies from 85% to 53% along with the increase of the GaN nanorod height. The reduction of polarization ratio has been attributed to the partial strain relaxation within the epitaxial structures as a result of growth on the GaN nanorod templates and the micro-size air-voids observed in the nanorod templates.
Investigation of emission polarization and strain in InGaN/GaN multiple quantum wells on nanorod epitaxially lateral overgrowth templates
(2012)
Huang, Huei-Min
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Lu, Tien-Chang
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Chang, Chiao-Yun
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Lan, Yu-Pin
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Ling, Shih-Chun
Non-polar (a-plane) InGaN/GaN multiple quantum wells (MQWs) on the GaN nanorod epitaxially lateral overgrowth templates with different nanorod height have been fabricated. The average in-plane strain in the InGaN MQWs has been determined from 2.73x10(-2) to 2.58x10(-2) while the nanorod height in templates increases from 0 to 1.7 mu m. The polarization ratio of the emission from InGaN MQWs varies from 85 % to 53 % along with the increase of the GaN nanorod height. The reduction of polarization ratio has been attributed to the partial strain relaxation within the epitaxial structures as a result of growth on the GaN nanorod templates and the micro-size air-voids observed in the nanorod templates.
Large-Area and Strain-Reduced Two-Dimensional Molybdenum Disulfide Monolayer Emitters on a Three-Dimensional Substrate
(2019-07-24)
Chang, Chiao-Yun
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Lin, Hsiang-Ting
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Lai, Ming-Sheng
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Yu, Cheng-Li
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Wu, Chong-Rong
Atomically thin membranes of two-dimensional (2-D) transition-metal dichalcogenides (TMDCs) have distinct emission properties, which can be utilized for realizing ultrathin optoelectronic integrated systems in the future. Growing a large-area and strain-reduced monolayer 2-D material on a three-dimensional (3-D) substrate with microstructures or nanostructures is a crucial technique because the electronic band structure of TMDC atomic layers is strongly affected by the number of stacked layers and strain. In this study, a large-area and strain-reduced MoS2 monolayer was fabricated on a 3D substrate through a two-step growth procedure. The material characteristics and optical properties of monolayer TMDCs fabricated on the nonplanar substrate were examined. The growth of monolayer MoS2 on a cone-shaped sapphire substrate effectively reduced the tensile strain induced by the substrate by decreasing the thermal expansion mismatch between the 2-D material and the substrate. Monolayer MoS2 grown on the nonplanar substrate exhibited uniform strain reduction and luminescence intensity. The fabrication of monolayer MoS2 on a nonplanar substrate increased the light extraction efficiency. In the future, large-area and strain-reduced 2-D TMDC materials grown on a nonplanar substrate can be employed as novel light-emitting devices for applications in lighting, communication, and displays for the development of ultrathin optoelectronic integrated systems.
Manipulation of nanoscale V-pits to optimize internal quantum efficiency of InGaN multiple quantum wells
(2015-03-02)
Chang, Chiao-Yun
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Li, Heng
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Shih, Yang-Ta
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Lu, Tien-Chang
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光電工程學系
We systematically investigated the influence of nanoscale V-pits on the internal quantum efficiency (IQE) of InGaN multiple quantum wells (MQWs) by adjusting the underlying superlattices (SLS). The analysis indicated that high barrier energy of sidewall MQWs on V-pits and long diffusion distance between the threading dislocation (TD) center and V-pit boundary were crucial to effectively passivate the non-radiative centers of TDs. For a larger V-pit, the thicker sidewall MQW on V-pit would decrease the barrier energy. On the contrary, a shorter distance between the TD center and V-pit boundary would be observed in a smaller V-pit, which could increase the carrier capturing capability of TDs. An optimized V-pit size of approximately 200-250 nm in our experiment could be concluded for MQWs with 15 pairs SLS, which exhibited an IQE value of 70%. (C) 2015 AIP Publishing LLC.
NONPOLAR GAN TWO DIMENSIONAL PHOTONIC CRYSTAL H2 HIGH QUALITY FACTOR NANOCAVITIES
(2013-01-01)
Lu, Tien-Chang
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Wu, Tzeng-Tsong
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Lo, Sheng-Yun
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Tsao, Che-Wei
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Huang, Huei-Min
Nonpolar GaN two-dimensional photonic crystal (PC) H2 nanocavities have been realized and investigated. One dominated resonant mode was demonstrated at 388 nm with quality factor of approximately 4300 at 77K. Moreover, the degree of polarization of the emission from the non-polar GaN PC nanocavity was measured to be 64% along the m crystalline direction.