Browsing by Author "Chang, Tsu-Chi"

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Collective Lasing Behavior of Monolithic GaN-InGaN Core-Shell Nanorod Lattice under Room Temperature
(2017-10-01)
Huang, Chia-Yen
;
Lin, Jing-Jie
;
Chang, Tsu-Chi
;
Liu, Che-Yu
;
Tai, Tzu-Ying
We demonstrated a monolithic GaN-InGaN core-shell nanorod lattice lasing under room temperature. The threshold pumping density was as low as 140 kW/cm(2) with a quality factor as high as 1940. The narrow mode spacing between lasing peaks suggested a strong coupling between adjacent whisper gallery modes (WGM), which was confirmed with the far field patterns. Excitation area dependent photoluminescence revealed that the long-wavelength lasing modes dominated the collective lasing behavior under a large excitation area. The excitation-area-dependent lasing behavior resulted from the prominent optical coupling among rods. According to the optical mode simulations and truncated-rod experiments, we confirmed that the fine-splitting of lasing peaks originated from the coupled supermodes existing in the periodic nanorod lattices. With wavelength-tunable active materials and a wafer-level scalable processing, patterning optically coupled GaN-InGaN core-shell nanorods is a highly practical approach for building various on-chip optical components including emitters and coupled resonator waveguides in visible and ultraviolet spectral range.
Curvature-assisted wave localization in Vertical Cavity Surface Emitting Lasers
(2017-01-01)
Hong, Kou-Bin
;
Lin, Chun-Yan
;
Chang, Tsu-Chi
;
Liang, Wei-Hsuan
;
Lai, Ying-Yu
By implementing surface structures in vertical cavity surface emitting lasers as manifolds for curved space, we experimentally study the impacts of geometrical constraints on wave localization. We observe localized waves pinned to the maximal curvature in an ellipticalring, and confirm the reduction in the localization length of waves by measuring near and far field patterns, as well as the corresponding dispersion relation. Theoretically, analyses based on a dissipative model with a parabola curve give good agreement remarkably to experimental measurement on the transition from delocalized to localized waves. The introduction of curved topology allows to control and design lasing modes in the nonlinear regime.
Demonstration of polarization control GaN-based micro-cavity lasers using a rigid high-contrast grating reflector
(2019-09-10)
Chang, Tsu-Chi
;
Kuo-Bin Hong
;
Kuo, Shuo-Yi
;
Lu, Tien-Chang
;
光電工程學系
We reported on GaN microcavity (MC) lasers combined with one rigid TiO2 high-contrast grating (HCG) structure as the output mirror. The HCG structure was directly fabricated on the GaN structure without an airgap. The entire MC structure comprised a bottom dielectric distributed Bragg reflector; a GaN cavity; and a top HCG reflector, which was designed to yield high reflectance for transverse magnetic (TM)- or transverse electric (TE)-polarized light. The MC device revealed an operation threshold of approximately 0.79 MW/cm(2) when pulsed optical pumping was conducted using the HCG structure at room temperature. The laser emission was TM polarized with a degree of polarization of 99.2% and had a small divergence angle of 14 degrees (full width at half maximum). This laser operation demonstration for the GaN-based MC structure employing an HCG exhibited the advantages of HCGs in semiconductor lasers at wavelengths from green to ultraviolet.
Design of photonic crystal surface emitting lasers with indium-tin-oxide top claddings
(2018-02-05)
Huang, Shen-Che
;
Hong, Kuo-Bin
;
Chiu, Han-Lun
;
Lan, Shao-Wun
;
Chang, Tsu-Chi
Electrically pumped GaAs-based photonic crystal surface emitting lasers were fabricated using a simple fabrication process by directly capping the indium-tin-oxide transparent conducting thin film as the top cladding layer upon a photonic crystal layer. Optimization of the separate-confinement heterostructures of a laser structure is crucial to improving characteristics by providing advantageous optical confinements. The turn-on voltage, series resistance, threshold current, and slope efficiency of the laser with a 100 x 100 mu m(2) photonic crystal area operated at room temperature were 1.3V, 1.5 Omega, 121mA, and 0.2W/A, respectively. Furthermore, we demonstrated a single-lobed lasing wavelength of 928.6 nm at 200mA and a wavelength redshift rate of 0.05 nm/K in temperature-dependent measurements. The device exhibited the maximum output power of approximately 400 mW at an injection current of 2 A; moreover, divergence angles of less than 1 degrees for the unpolarized circular-shaped laser beam were measured at various injection currents. Overall, the low threshold current, excellent beam quality, small divergence, high output power, and high-operating-temperature (up to 343K) of our devices indicate that they can potentially fill the requirements for next-generation light sources and optoelectronic devices. Published by AIP Publishing.
Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors
(2020-04-15)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Hong, Kuo-Bin
;
Bengtsson, Jorgen
;
Gustaysson, Johan
We demonstrate the first electrically injected GaNbased vertical-cavity surface-emitting lasers (VCSELs) with a TiO2 high-index-contrast grating (HCG) as the top mirror. Replacing the top distributed Bragg reflector (DBR) with an HCG offers substantial thickness reduction, polarization-pinning, and setting of the resonance wavelength by the grating parameters. Conventional HCGs are usually suspended in the low refractive index material, such as air, in order to create the largest refractive index contrast. However, the mechanical stability of such structures can be questioned and creating free-hanging GaN-membrane on top of GaN is problematic. We have therefore fabricated TiO2-HCGs resting directly on GaN without an air-gap. No DBR layers are used below the HCG to boost the reflectivity. A VCSEL with an aperture diameter of 10 mu m shows a threshold current of 25 mA under pulsed operation at room temperature. The lasing modes locate around 400 nm and are transversely electrically -polarized with a line width of 0.5 nm. The full-width half-maximum beam divergence is 10 degrees. This demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as postgrowth setting of the resonance wavelength.
Electrically Pumped III-N Microcavity Light Emitters Incorporating an Oxide Confinement Aperture
(2017-01-05)
Lai, Ying-Yu
;
Chang, Tsu-Chi
;
Li, Ya-Chen
;
Lu, Tien-Chang
;
Wang, Shing-Chung
In this work, we report on electrically pumped III-N microcavity (MC) light emitters incorporating oxide confinement apertures. The utilized SiO2 aperture can provide a planar ITO design with a higher index contrast (similar to 1) over other previously reported approaches. The fabricated MC light emitter with a 15-mu m-aperture shows a turn-on voltage of 3.3 V, which is comparable to conventional light emitting diodes (LEDs), showing a good electrical property of the proposed structure. A uniform light output profile within the emission aperture suggesting the good capability of current spreading and current confinement of ITO and SiO2 aperture, respectively. Although the quality factor (Q) of fabricated MC is not high enough to achieve lasing action (similar to 500), a superlinear emission can still be reached under a high current injection density (2.83 kA/cm(2)) at 77 K through the exciton-exciton scattering, indicating the high potential of this structure for realizing excitonic vertical-cavity surface-emitting laser (VCSEL) action or even polariton laser after fabrication optimization.
Engineering radiative coupling of excitons in 2D semiconductors
(2019-11-20)
Horng, Jason
;
Chou, Yu-Hsun
;
Chang, Tsu-Chi
;
Hsu, Chu-Yuan
;
Lu, Tien-Chang
The resonance energy and the transition rate of atoms, molecules, and solids were understood as their intrinsic properties in classical electromagnetism. It was later realized that these quantities are linked to the radiative coupling between the transition dipole and photon modes. Such effects can be greatly amplified in macroscopic many-body systems from virtual photon exchange between dipoles, but are often masked by inhomogeneity and pure dephasing, especially in solids. Here, we observe in both absorption and emission spectroscopy the renormalization of the exciton resonance and the radiative decay rate in transition metal dichalcogenides monolayers due to their radiative interactions. Tuning the photon mode density near the monolayer, we demonstrate control of cooperative Lamb shift, radiative decay, and valley polarization of the excitons as well as control of the charged exciton emission. Our work establishes a technologically accessible and robust experimental system for engineering cooperative matter-light interactions. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
GaN vertical-cavity surface-emitting laser with a high-contrast grating reflector
(2018-01-01)
Chang, Tsu-Chi
;
Kuo, Shuo-Yi
;
Hashemi, Ehsan
;
Haglund, Asa
;
Lu, Tien-Chang
We report a GaN-based VCSEL with a high-contrast grating (HCG) as the top mirror. The HCG consisted of TiO2 and rested directly on the n-GaN without an airgap or the use of any DBR layers to boost the reflectivity. The full VCSEL structure was optically pumped at room temperature and showed a lasing threshold of approximately 0.69MW/cm(2) and a lasing wavelength at 369.1 nm. This first demonstration of lasing in a HCG GaN based VCSEL opens up the possibility to explore all the potential benefits of HCGs in the blue and ultraviolet spectral regime.
GaN-based vertical-cavity surface-emitting laser incorporating a TiO2 high-index-contrast grating
(2020-01-01)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Bengtsson, Jorgen
;
Gustavsson, Johan
;
Haglund, Asa
We demonstrate the first electrically injected GaN-based VCSEL with a TiO2 high-contrast grating (HCG) as the top mirror. The TiO2-HCG rested directly on the n-GaN without an airgap for mechanical stability. A VCSEL with an aperture diameter of 10 mu m had a threshold current of 25 mA under pulsed operation at room temperature. Multiple longitudinal modes coexist around 400 nm, each TM-polarized with a linewidth of 0.5 nm (spectral resolution limited). This first demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as post-growth setting of resonance wavelength.
GaN-based vertical-cavity surface-emitting lasers operating at high temperature
(2017-01-01)
Chang, Tsu-Chi
;
Kuo, Shiou-Yi
;
Lian, Jhen-Ting
;
Hong, Kuo-Bin
;
Lu, Tien-Chang
We report on GaN-based vertical-cavity surface emitting lasers (VCSELs) capable of high temperature operation. The structures of VCSELs include double dielectric distributed Bragg reflectors and bonded to a silicon substrate with a p-side-down configuration, allowing a better heat dissipation. The temperature dependent lasing characteristics of VCSELs can sustain to 350K.
Generation of Crescent Waves in Vertical Cavity Surface Emitting Lasers with an Surface Elliptical Ring
(2014)
Lai, Ying-Yu
;
Chang, Tsu-Chi
;
Li, Ya-Chen
;
Lin, Chun-Yan
;
Lu, Tien-Chang
We tailor the lasing modes in the vertical cavity surface -emitting laser into a crescent wave using a surface elliptical ring. The crescent wave was observed to be localized at the semi-major axis of elliptical ring.
Growth of GaN on Patterned Sapphire Substrate with High-Index Facets
(2015-01-01)
Chang, Sheng-Chieh
;
Chen, Chien-Chih
;
Chang, Tsu-Chi
;
Lin, Kun-Lin
;
Lu, Tien-Chang
Periodic pyramidal array patterned sapphire substrate (PSS) with various inclined facets was fabricated by wet etching. It was found that {3 (4) over bar 17}, {4 (1) over bar(3) over bar 18}, and {12 (3) over bar5} facets are exposed on the PSS structure after etching. GaN grown on the PSS by metal-organic chemical vapor deposition was found to have a semi-polar orientation by structural characterization with scanning and transmission electron microscopy. Also, the results show that GaN is mainly grown on the {12 (3) over bar5} sapphire facet with the orientation relationship between GaN and sapphire as(01 (1) over bar(4) over bar)(GaN) // (3 (3) over bar0 (6) over bar)(sapphire) and [02 (2) over bar1](GaN) // [11 (2) over bar0](sapphire), and the dislocation density in the grown GaN decreased with thickness. In addition, photoluminescence and catholuminescence measurements show only strong near-band-edge emission from the semi-polar GaN on the {12 (3) over bar5} sapphire facet. (C) 2015 The Electrochemical Society. All rights reserved.
High-temperature operation of GaN-based vertical-cavity surface-emitting lasers
(2017-11-01)
Chang, Tsu-Chi
;
Kuo, Shiou-Yi
;
Lian, Jhen-Ting
;
Hong, Kuo-Bin
;
Wang, Shing-Chung
We report GaN-based vertical-cavity surface-emitting lasers (VCSELs) capable of high-temperature operation. The GaN-based VCSELs include double dielectric distributed Bragg reflectors and epitaxially grown p-i-n InGaN multiple-quantum-well active layers initially deposited on c-plane sapphire substrates that are bonded to a silicon substrate with a p-side-down and patterned mirror configuration, allowing effective heat dissipation. GaN-based VCSELs with an emission aperture 10 mu m in diameter were fabricated, and their temperature-dependent lasing characteristics revealed that the VCSELs can endure 350 K, as measured under quasicontinuous-wave operation conditions. The temperature-dependent lasing wavelength shift occurs at a rate of d lambda(FP)/dT approximate to 0.012nm/K. The high-temperature operation of GaN-based VCSELs was attributed to the well-matched gain-mode offset, the p-side-down configuration, and the reduced lateral size of the bottom distributed Bragg reflector with recessed metal. (C) 2017 The Japan Society of Applied Physics
Lasing action in GaN-based VCSELs with top high-contrast grating reflectors
(2018-01-01)
Chang, Tsu-Chi
;
Kuo, Shuo-Yi
;
Hashemi, Ehsan
;
Haglund, Asa
;
Lu, Tien-Chang
We report a GaN-based VCSEL with a high-contrast grating (HCG) as the top mirror. The HCG consisted of TiO2 and rested directly on the n-GaN without an airgap or the use of any DBR layers to boost the reflectivity. The full VCSEL structure was optically pumped at room temperature and showed a lasing threshold of approximately 0.99 MW/cm(2) and a lasing wavelength at 369.8 nm. The demonstration of HCG GaN-based VCSEL opens up the possibility to explore all the potential benefits of HCGs in the blue and ultraviolet spectral regime.
Lasing in a ZnO membrane microcavity with designable shape fabricated by focused ion beam milling
(2015)
Chang, Tsu-Chi
;
Lai, Ying-Yu
;
Chou, Yu-Hsun
;
Lu, Tien-Chang
;
照明與能源光電研究所
We show a three-dimensional membrane cavity fabrication technique and corresponding lasing characteristics of the fabricated rectangular ZnO membrane microcavity (MC) using optical injection. The ZnO membrane was cut from a single crystalline ZnO substrate by using a focused ion beam, and was then placed onto a SiO2 substrate by using a glass tip. The micro-photoluminescence measurement performed on the fabricated ZnO membrane MC at 77 K showed an obvious feature of lasing action including non-linear increasing of intensity and linewidth narrowing. By using this fabrication approach, various MCs with desired shapes can be made.
Lasing on nonlinear localized waves in curved geometry
(2017-11-13)
Hong, Kou-Bin
;
Lin, Chun-Yan
;
Chang, Tsu-Chi
;
Liang, Wei-Hsuan
;
Lai, Ying-Yu
The use of geometrical constraints exposes many new perspectives in photonics and in the fundamental studies of nonlinear waves. By implementing surface structures in vertical cavity surface emitting lasers as manifolds for curved space, we experimentally study the impacts of geometrical constraints on nonlinear wave localization. We observe localized waves pinned to the maximal curvature in an elliptical-ring, and confirm the reduction in the localization length of waves by measuring near and far field patterns, as well as the corresponding energy-angle dispersion relation. Theoretically, analyses based on a dissipative model with a parabola curve give good agreement remarkably to experimental measurement on the reduction in the localization length. The introduction of curved geometry allows to control and design lasing modes in the nonlinear regime. (C) 2017 Optical Society of America
Manipulation of exciton and photon lasing in a membrane-type ZnO microcavity
(2015-03-30)
Lai, Ying-Yu
;
Chen, Jee-Wei
;
Chang, Tsu-Chi
;
Chou, Yu-Hsun
;
Lu, Tien-Chang
We report on the fabrication and characterization of a membrane-type ZnO microcavity (MC). The ZnO membrane was cut from a single crystalline ZnO substrate by using focused ion beam milling, and was then placed onto a SiO2 substrate by using glass microtweezers. Through changing the pumping regime, manipulation of P-band exciton lasing and whispering-gallery mode (WGM) photon lasing could be easily achieved. P-band exciton lasing was observed only when the pumping laser was focused at the center of the ZnO MC with a small pumping size because of the innate ring-shaped WGM distribution. Furthermore, the lasing threshold of the ZnO MC could be reduced to an order lower by using a larger pumping spot because of the more favorable spatial overlap between the optical gain and WGM. (C) 2015 AIP Publishing LLC.
Mode-Hopping Phenomena in the InGaN-Based Core-Shell Nanorod Array Collective Lasing
(2018-07-01)
Huang, Chia-Yen
;
Tai, Tzu-Ying
;
Lin, Jing-Jie
;
Chang, Tsu-Chi
;
Liu, Che-Yu
A two-dimensional monolithic InGaN-based core-shell it array was excited under a varying temperature. We observed an abrupt dominant mode hopping from 3.29 to 141 eV in the collective lasing as the temperature decreased from T = 240 to 225 K, Photoluminescence under a near-threshold pumping density revealed the splitting of spontaneous emission. between the core and the shell with a decreasing temperature. The bandgap evolution of GaN and InGaN showed opposite trends due to the interaction of temperature effects and bandgap renormalization effects. Theoretical simulation revealed the differences of gain spectra evolution between room lire and to temperature due to the difference the carrier dynamics, In the optically coupled nanorod array, the dominant lasing;mode was not only determined by it structure, but also strongly influenced by external operating conditions. Rattier than singular microcavity lasers the coupled nanorod array demonstrated a broader parameter space for on-chip wavelength manipulation.
Mode-switching phenomena in periodic InGaN-based hexagon microcavity array
(2018-01-01)
Huang, Chia-Yen
;
Dai, Tzu-Ying
;
Lin, Jing-Jie
;
Chang, Tsu-Chi
;
Liu, Che-Yu
The lasing behavior of InGaN-based microcavity array was strongly relevant to the excitation area. The stronger rod-to-rod optical interaction between the fundamental axial mode resulted its dominance in the collective lasing behavior.
Monolithic GaN-InGaNCore-shell Lasers in Submicron Scale
(2017-01-01)
Huang, Chia-Yen
;
Lin, Jing-Jie
;
Chang, Tsu-Chi
;
Liu, Che-Yu
;
Dai, Tzu-Ying
We demonstrated a GaN-InGaN core-shell nanorod periodic array lasing under room temperature. Optical simulations and photoluminescence measurement revealed optically-coupled whisper gallery modes. The threshold pumping density was 80 kW/cm(2) with a quality factor of 1940.