Browsing by Author "Hong, Kuo-Bin"

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Analysis of Quality Factor Enhancement in the Monolithic InGaN/GaN Nanorod Array
(2019-04-01)
Huang, Chia-Yen
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Tai, Tzu-Ying
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Hong, Kuo-Bin
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Kuo, Hao-Chung
;
Lu, Tien-Chang
Whispering gallery mode (WGM) lasers and resonators are key building blocks for photonic integrated circuits. The quality factor and resonant wavelength are strong functions of the cavity size. Nanoscale WGM cavities suffer from a low-quality factor due to prominent scattering loss. However, the quality factor could be enhanced by forming an optically-coupled rod array or photonic molecules. Through simulations, we revealed how rod-to-rod optical coupling influenced the threshold pumping level and dominant mode selection, where the trend showed good agreement with the experimental observation. According to the simulation, the quality factor could be enhanced by up to eight times by forming a six-rod photonic molecule. The quality factor and effective mode were both superior to the single rods with the same wafer device footprint.
Anti-guiding and guiding effects in GaN-based vertical-cavity surface-emitting lasers
(2020-02-01)
Chen, Lih-Ren
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Chen, Bo-Yan
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Kuo, Shiou-Yi
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Hong, Kuo-Bin
;
Lu, Tien-Chang
We study the lateral optical confinement effect on the performance and lasing characteristics of GaN-based vertical-cavity surface-emitting lasers (VCSELs). The anti-guiding and guiding structures are designed by calculating the effective refractive index difference of active and cladding regions. By varying the compensation layer configuration and thickness, the designed effective refractive index of the active region is 0.44% higher than peripheral for the guiding structure. The threshold current density of VCSEL with the guiding structure is 25.4 kA/cm(2), which is almost half of that with the anti-guiding structure showing 53.5 kA/cm(2). For the anti-guiding structure, the signals from both active and cladding regions are observed by the far-field angle-resolved spectrum at 1.4 x I-th driving current, which agrees well with our simulation. Throughout the study, we show the advantage of the guiding structure both theoretically and experimentally. Moreover, an effective guiding structure is obtained by a proper design and simple device process, which will be very promising for mass production.
Collective Lasing Behavior of Monolithic GaN-InGaN Core-Shell Nanorod Lattice under Room Temperature
(2017-10-01)
Huang, Chia-Yen
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Lin, Jing-Jie
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Chang, Tsu-Chi
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Liu, Che-Yu
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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.
Controllable lasing performance in solution-processed organic-inorganic hybrid perovskites
(2016)
Kao, Tsung Sheng
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Chou, Yu-Hsun
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Hong, Kuo-Bin
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Huang, Jiong-Fu
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Chou, Chun-Hsien
Solution-processed organic-inorganic perovskites are fascinating due to their remarkable photo-conversion efficiency and great potential in the cost-effective, versatile and large-scale manufacturing of opto-electronic devices. In this paper, we demonstrate that the perovskite nanocrystal sizes can be simply controlled by manipulating the precursor solution concentrations in a two-step sequential deposition process, thus achieving the feasible tunability of excitonic properties and lasing performance in hybrid metal-halide perovskites. The lasing threshold is at around 230 mu J cm(-2) in this solution-processed organic-inorganic lead-halide material, which is comparable to the colloidal quantum dot lasers. The efficient stimulated emission originates from the multiple random scattering provided by the micro-meter scale rugged morphology and polycrystalline grain boundaries. Thus the excitonic properties in perovskites exhibit high correlation with the formed morphology of the perovskite nanocrystals. Compared to the conventional lasers normally serving as a coherent light source, the perovskite random lasers are promising in making low-cost thin-film lasing devices for flexible and speckle-free imaging applications.
Design of photonic crystal surface emitting lasers with indium-tin-oxide top claddings
(2018-02-05)
Huang, Shen-Che
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Hong, Kuo-Bin
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Chiu, Han-Lun
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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.
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
;
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.
Electrically driven GaAs-based photonic crystal lasers with ITO cladding layers
(2018-01-01)
Huang, Shen-Che
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Hong, Kuo-Bin
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Chiu, Han-Lun
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Lan, Shao-Wun
;
Lu, Tien-Chang
Photonic crystal (PhC) laser, with specific merits of low astigmatism, single mode operation and integration into silicon photonic system, has been studied for many years. Compared with the edge emitting lasers (EELs), surface emitting light emitters have many advantages such as small and symmetric divergence angle and platform of array-based capability. The resonance along in-plane direction preserves the high modal gain to overcome optical loss and leads to lasing action. These photonic crystal designs which has superior essential performance to that of next-generation light sources which can propose to tunable lasing multi-wavelengths with polarization control and single-mode high beam-quality. In this report, we demonstrate the fabricated realization of a novel electrically driven high-power PhC laser incorporating indium-tin-oxide (ITO) layer as a newly designed cladding layer, which could improve the laser characteristics and achieve the much lower cost of the integrated optoelectronic application. The series of investigated actual nano fabrication lasing devices with distinct designs were observed to verify the structural parameters including grating periods and area regions by tailoring the photonic crystal structure. Based upon experimental results, lasing characteristics through high current injection at room temperature inclusive of I-V curves, L-I curves, near/far field patterns, and lasing spectra were characterized and discussed. We believe this practical watt-level light output achievement should have an impact on numerous photonic devices of the coherent operations and helpful attribution to the two-dimension integrated platform in the future.
Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors
(2020-04-15)
Chang, Tsu-Chi
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Hashemi, Ehsan
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Hong, Kuo-Bin
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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 quantum dot surface emitting lasers with Bragg grating capped by ITO cladding layers
(2016)
Hong, Kuo-Bin
;
Chang, Ting-Yuan
;
Pan, Chien-Hung
;
Lin, Chien-Hung
;
Lin, Gray
QD based Bragg gratings surface emitting lasers using ITO as transparent cladding layers were demonstrated. Measured lasing peak locates at 1298nm and threshold current density of 210 A/cm(2). The laser shows extremely small divergence surface-emitted beam and thermal redshift of 0.08 nm/K in peak wavelength.
Enhanced Lasing Performance in Solution-processed Lead Halide Perovskites Covered with PMMA and Ag
(2016)
Kao, Tsung Sheng
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Chou, Yu-Hsun
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Hong, Kuo-Bin
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Huang, Jiong-Fu
;
Chen, Fang-Chung
We report the enhanced lasing performance in lead-halide perovskites covered with PMMA and Ag. Not only the perovskite can be protected from hydrolysis, but also the lasing thresholds can be greatly reduced resulting from the plasmonic effect.
Enhanced Light Output of UVA GaN Vertical LEDs With Novel DBR Mirrors
(2015-12-01)
Kuo, Shiou-Yi
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Hong, Kuo-Bin
;
Lu, Tien-Chang
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交大名義發表
;
National Chiao Tung University
The emission efficiency of GaN-based light-emitting diodes (LEDs) decreases significantly as the emission wavelength is shorter than 370 nm because of the absorption of emission light in the GaN layers. The vertical LED structure could be applied to avoid the absorption problem, because the undoped GaN layer would be removed and the n-GaN layer could be thinned as much as possible in the fabrication process. In this report, we propose a novel ultraviolet (UV) LED structure with a thin indium-tinoxide (ITO) layer as the ohmic contact and a dielectric distributed Bragg reflector (DBR) as the high reflectivity mirror. Comparing referenced vertical UV LED structures with ITO/Ag as the metal mirror, the vertical UV LED with the ITO/DBR mirror shows the output power of approximately 190 mW at 350 mA with 7.9% enhancement.
Enhanced wavelength-selective photoresponsivity with a MoS2 bilayer grown conformally on a patterned sapphire substrate
(2019-02-14)
Chen, Sung-Wen Huang
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Wang, Sheng-Wen
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Hong, Kuo-Bin
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Medin, Henry
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Chung, Chieh-Han
In the present study, novel MoS2 bilayers with 3D structures were considered for their application as wavelength-sensitive photodetectors. Using e-gun deposition and a CVD process, MoS2 bilayers can be grown conformally on a patterned (cones or pyramids) sapphire substrate without any wrinkles on the 2D film. After the sulfurization process, the MoS2 bilayer is subjected to a local strain in the patterns and its band gap gets enlarged due to the strain. This phenomenon is beneficial for photo-devices to enable the collection of the photocurrent. Measurements revealed a broadband enhancement of the MoS2-based photodetector with a patterned array in terms of both absorption and photocurrent. It is noteworthy that a cone-patterned sapphire substrate (CPSS) is able to generate more photocurrent when illuminated under blue light illumination, whereas the pyramid-patterned sapphire substrate (PPSS) performs best under green and red light illumination. Simulations of the electric field distributions for MoS2 coatings on different substrates, based on 3D models, revealed that the sensitivity of the MoS2-based photodetector can be greatly enhanced by the light-scattering effect.
Exciton-polariton Josephson junctions at finite temperatures
(2017-08-25)
Lebedev, M. E.
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Dolinina, D. A.
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Hong, Kuo-Bin
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Lu, Tien-Chang
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Kavokin, A. V.
We consider finite temperature effects in a non-standard Bose-Hubbard model for an exciton-polariton Josephson junction (JJ) that is characterised by complicated potential energy landscapes (PEL) consisting of sets of barriers and wells. We show that the transition between thermal activation (classical) and tunneling (quantum) regimes exhibits universal features of the first and second order phase transition (PT) depending on the PEL for two polariton condensates that might be described as transition from the thermal to the quantum annealing regime. In the presence of dissipation the relative phase of two condensates exhibits non-equilibrium PT from the quantum regime characterized by efficient tunneling of polaritons to the regime of permanent Josephson or Rabi oscillations, where the tunneling is suppressed, respectively. This analysis paves the way for the application of coupled polariton condensates for the realisation of a quantum annealing algorithm in presently experimentally accessible semiconductor microcavities possessing high (105 and more) Q-factors.
Flexible Organometal-Halide Perovskite Lasers for Speckle Reduction in Imaging Projection
(2019-05-01)
Wang, Yu-Chi
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Li, Heng
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Hong, Yu-Heng
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Hong, Kuo-Bin
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Chen, Fang-Chung
Disorder is emerging as a strategy for fabricating random laser sources with very promising materials, such as perovskites, for which standard laser cavities are not effective or too expensive. We need, however, different fabrication protocols and technologies for reducing the laser threshold and controlling its emission. Here, we demonstrate an effectively solvent-engineered method for high-quality perovskite thin films on a flexible polyimide substrate. The fractal perovskite thin films exhibit excellent optical properties at room temperature and easily achieve lasing action without any laser cavity above room temperature with a low pumping threshold. The lasing action is also observed in curved perovskite thin films on flexible substrates. The lasing threshold can be further reduced by increasing the local curvature, which modifies the scattering strengths of the bent thin film. We also show that the curved perovskite lasers are extremely robust with respect to repeated deformations. Because of the low spatial coherence, these curved random laser devices are efficient and durable speckle-free light sources for applications in spectroscopy, bioimaging, and illumination.
Full-Spectrum Analysis of Perovskite-Based Surface Plasmon Nanolasers
(2020-03-29)
Cheng, Pi-Ju
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Zheng, Qi-Yan
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Hsu, Chu-Yuan
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Li, Heng
;
Hong, Kuo-Bin
We systematically studied the characteristics of hybrid perovskite-based surface plasmon nanolasers. If one changes the anion composition of perovskites, the emission wavelength can be easily tuned. We conducted in full-spectrum modeling that featured hybrid perovskite nanowires placed on different SiO2-coated metallic (Au, Ag, and Al) plates. The proposed nanocavities that supported plasmonic gap modes exhibited distinguished properties of nanolasers, such as low-transparency threshold-gain and low lasing threshold. The corresponding experimental results for the MAPbBr(3) nanolaser on Ag revealed the low-threshold operation. These superior features were attributed to enhanced light-matter interaction with strong coupling. Therefore, the proposed scheme, integrated with hybrid perovskite as gain material, provides an excellent platform for nanoscale plasmon lasing in the visible to near-infrared spectra.
GaN-based vertical-cavity surface-emitting lasers operating at high temperature
(2017-01-01)
Chang, Tsu-Chi
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Kuo, Shiou-Yi
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Lian, Jhen-Ting
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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.
High Reflectance Patterned Substrate Designed for Optical Devices
(2015)
Lan, Yu-Pin
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Wu, Yung-Chi
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Lin, Da-Wei
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Hong, Kuo-Bin
;
Lee, Chia-Yu
This article proposed an approach by using patterned sapphire substrate to act as a 2-dimensional distributed Bragg reflector (DBR) mirror to increase the output power of LEDs.
High-Efficiency InGaN/GaN Core-Shell Nanorod Light-Emitting Diodes With Low-Peak Blueshift and Efficiency Droop
(2017-03)
Tzou, An-Jye
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Hsieh, Dan-Hua
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Hong, Kuo-Bin
;
Lin, Da-Wei
;
Huang, Jhih-Kai
In this study, novel three-dimensional (3-D) nanoscale structures and methodology are demonstrated for application in high-efficiency core-shell nanorod (NR) light-emitting diodes (LEDs). The key to our successful growth of the structures is the introduction of passivation, which can be used to selectively grow active layers in desired structures. Through the fabrication methodology, core-shell NR green LEDs exhibiting large nonpolar active region and homogeneous indium distributions without a point tip shape were achieved. Stable light emission at a central wavelength of 518 nm was achieved as the injected current increased to more than 40 mA. The improved NR LEDs exhibited a stable luminescence emission wavelength (blueshift of 62 nm) and low-efficiency droop (18.1%) at 200 mA. Our scheme is scalable and compatible with current technologies, which provides a new perspective for developing high-performance, 3-D nanoscale optoelectronic devices.
High-operation-temperature Aluminum-based SPP Nanolasers
(2016)
Chou, Yu-Hsun
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Hong, Kuo-Bin
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Chou, Bo-Tsun
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Wu, Yen-Mo
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Shih, Jheng-Hong
Metal-insulator-semiconductor structures has widely adopted in plasmonics lasers. However, we found that the insulator is not necessary if permittivity combination of laser structures is properly designed. Single-mode laser operation was demonstrate in devices without artificial insulator layers. Moreover, the operation temperature can achieve to 353 K.
High-Operation-Temperature Plasmonic Nanolasers on Single-Crystalline Aluminum
(2016-05)
Chou, Yu-Hsun
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Wu, Yen-Mo
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Hong, Kuo-Bin
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Chou, Bo-Tsun
;
Shih, Jheng-Hong
The recent development of plasmonics has overcome the optical diffraction limit and fostered the development of several important components including nanolasers, low-operation-power modulators, and high-speed detectors. In particular, the advent of surface-plasmon-polariton (SPP) nanolasers has enabled the development of coherent emitters approaching the nanoscale. SPP nanolasers widely adopted metal insulator semiconductor structures because the presence of an insulator can prevent large metal loss. However, the insulator is not necessary if permittivity combination of laser structures is properly designed. Here, we experimentally demonstrate a SPP nanolaser with a ZnO nanowire on the as-grown single-crystalline aluminum. The average lasing threshold of this simple structure is 20 MW/cm(2), which is four-times lower than that of structures with additional insulator layers. Furthermore, single-mode laser operation can be sustained at temperatures up to 353 K. Our study represents a major step toward the practical realization of SPP nanolasers.