Browsing by Author "Chang, Shu-Wei"

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A 256x128 energy-efficient TCAM with novel low power schemes
(2007)
Huang, Po-Tsang
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Chang, Shu-Wei
;
Liu, Wen-Yen
;
Hwang, Wei
;
電子工程學系及電子研究所
Novel low power schemes for energy-efficient ternary content-addressable memory (TCAM) are presented in this paper. The butterfly match-line scheme is based on the pseudo-footless clock-data pre-charged architecture. It connects each pipelined stage in a butterfly style which significantly decreases both search time and power consumption. For applications like IP-address forwarding in a network router, a new don't-care based power gating and don't-care based hierarchical (DCBH) search-line scheme are proposed. The search-line is divided into global search-line (GSL) and local search-line (LSL) which is controlled by don't-care state in DCBH search-line scheme. Therefore, the power consumption on search line is reduced without any search time overhead. Besides, the power saving of the standby power is achieved by power gating technique. The proposed 256 x 128bit TCAM has been implemented with TSMC 0.13um CMOS technology. It shows 0.55ns of match evaluation time on search operation with 0.29 fJ/bit/search of energy efficiency.
Absorption enhancement in type-II coupled quantum rings due to existence of quasi-bound states
(2018-01-01)
Hsieh, Chi-Ti
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Lin, Shih-Yen
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Chang, Shu-Wei
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光電工程學系
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Department of Photonics
The absorption of type-II nanostructures is often weaker than type-I counterpart due to spatially separated electrons and holes. We model the bound-to-continuum absorption of type-II quantum rings (QRs) using a multiband source-radiation approach using the retarded Green function in the cylindrical coordinate system. The selection rules due to the circular symmetry for allowed transitions of absorption are utilized. The bound-to continuum absorptions of type-II GaSb coupled and uncoupled QRs embedded in GaAs matrix are compared here. The GaSb QRs act as energy barriers for electrons but potential wells for holes. For the coupled QR structure, the region sandwiched between two QRs forms a potential reservoir of quasi-bound electrons. Electrons in these states, though look like bound ones, would ultimately tunnel out of the reservoir through barriers. Multiband perfectly-matched layers are introduced to model the tunneling of quasi-bound states into open space. Resonance peaks are observed on the absorption spectra of type-II coupled QRs due to the formation of quasi-bound states in conduction bands, but no resonance exist in the uncoupled QR. The tunneling time of these metastable states can be extracted from the resonance and is in the order of ten femtoseconds. Absorption of coupled QRs is significantly enhanced as compared to that of uncoupled ones in certain spectral windows of interest. These features may improve the performance of photon detectors and photovoltaic devices based on type-II semiconductor nanostructures.
Bidirectionality in Bianistropic but Reciprocal Photonic Crystals and Its Usage in Active Photonics
(2014-01-01)
Chang, Shu-Wei
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光電工程學系
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Department of Photonics
We show that the bidirectionality of optical modes exists in general bianisotropic but reciprocal photonic crystals and related structures. Using this property, we obtain an alternative bidirectionality of modes with sources (gain) in active photonic crystals. In the former, we conclude that degeneracies of modes with complex anti-parallel wave vectors are always identical as long as the structure is reciprocal. With the latter, we setup an associated biorthogonality relation in the Rayleigh-Carson form for modes in active photonic crystals.
Bound-to-continuum absorption with tunneling in type-II nanostructures: a multiband source-radiation approach
(2013-12-16)
Hsieh, Chi-Ti
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Chang, Shu-Wei
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光電工程學系
;
Department of Photonics
We convert calculations of the bound-to-continuum absorption in type-II semiconductor quantum wells into an equivalent source-radiation problem under the effective-mass approximation with band mixing. Perfectly matched layers corresponding to the eight-band Luttinger-Kohn Hamiltonian are introduced to incorporate the effect of quasi-bound states in open regions. In this way, the interplay between quantum tunneling and optical transitions is fully taken into account. From resulted lineshapes of the Fano resonance, we can evaluate tunneling rates of these metastable states and related absorption strengths relative to those of the continuum. The approach here is useful in estimations of carrier extraction rates from type-II nanostructures for photovoltaic applications. (C) 2013 Optical Society of America
BUTTERFLY MATCH-LINE STRUCTURE AND SEARCH METHOD IMPLEMENTED THEREBY
(2008-07-24)
Huang, Po-Tsang
;
Hwang, Wei
;
Chang, Shu-Wei
The present invention discloses a butterfly match-line structure and a search method implemented thereby, wherein the parallelism of the match lines is increased to shorten the search time, and a butterfly-type connection is used to reduce the power consumption and achieve the best energy efficiency. Via the butterfly-type connection, information can be reciprocally transmitted between the parallel match lines, which are independent originally. When a miss case occurs, more succeeding memory cells will not be compared but will be turned off. Thereby, the power consumption is reduced. Further, XOR-based conditional keepers are used to reduce the matching time and the power consumption. Besides, such a circuit is also used to shorten the delay time of the butterfly-type connection.
Carrier lifetime of heavily p-doped base in light-emitting transistors and transistor lasers
(2019-01-01)
Hsieh, Chi-Ti
;
Cheng, Pi-Ju
;
Lin, Chih-Hsien
;
Chang, Shu-Wei
;
光電工程學系
Light-emitting transistor (LET) and transistor laser (TL) can provide the high-speed electrical and optical modulations simultaneously, advancing light-emitting diodes and diode lasers. Still, between experimental data and rate-equation modeling, there are two-order-of-magnitude uncertainties on the carrier lifetimes of quantum wells (QWs) inserted in heavily p-doped bases of these devices. In view of the importance of this timescale on the modulation speed, we provide a comprehensive approach to calculate carrier lifetimes under such circumstances. We model the Hartree potential energy with self-consistent solutions of the Schrodinger's and Poisson's equations. The hole distribution is obtained from real-space density of states through multiband retarded Green functions, taking the outgoing-wave features of hole quasi-bound states into account. We then estimate the carrier lifetimes based on a multiband source-radiation approach including both bound-to-bound and bound-to-continuum components of spontaneous (SP) emissions. Under low surface carrier injections, a large Hartree potential is formed, and the valence band around the QW is strongly tilted. Both bound and quasi-bound valence states are present, and quasi-bound holes may tunnel out of QW and reemerge in the base. The SP spectrum from the QW in the heavily doped base is significantly larger than that from an undoped one due to preexisting holes. At the high injection level, the screening effect significantly reduces the Hartree potential and band bending. We also include the nonradiative Auger recombination to evaluate the total carrier lifetime. Overall carrier lifetimes and small-signal ones are estimated as hundred picoseconds at a doping density of 10(19)cm(-3) and might be even shorter in the case of heavier doping.
Characteristics of Blue GaN/InGaN Quantum-Well Light-Emitting Transistor
(2020-01-01)
Lan, Hao-Yu
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Tseng, I-Chen
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Lin, Yung-Hsiang
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Chang, Shu-Wei
;
Wu, Chao-Hsin
We demonstrate simultaneous electrical and optical modulations of the first GaN/InGaN quantum-well light-emitting transistor (QW-LET) which contains an In-0.15 Ga0.85N QW in the heavily p-doped In-0.05 Ga0.95N base. Unlike GaAs/InGaAs counterparts, the GaN/InGaN QW- LET has a current gain (up to 5) and optical power which increases linearly with the base current. Its emission spectra are centered at a wavelength of 420 nm and barely shift with the current injection, in contrast to the behavior of typical nitride-based LEDs. The unusual features of this device may be related to the tilted band profile induced by the polarization field in the QW and issue of p-type doping.
Chiral Second-Harmonic Generation from Monolayer WS2/Aluminum Plasmonic Vortex Metalens
(2020-04-08)
Guo, Wan-Ping
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Liang, Wei-Yun
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Cheng, Chang-Wei
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Wu, Wei-Lin
;
Wang, Yen-Ting
Two-dimensional spiral plasmonic structures have emerged as a versatile approach to generate near-field vortex fields with tunable topological charges. We demonstrate here a far-field approach to observe the chiral second-harmonic generation (SHG) at designated visible wavelengths from a single plasmonic vortex metalens. This metalens comprises an Archimedean spiral slit fabricated on atomically flat aluminum epitaxial film, which allows for precise tuning of plasmonic resonances and subsequent transfer of two-dimensional materials on top of the spiral slit. The nonlinear optical measurements show a giant SHG circular dichroism. Furthermore, we have achieved an enhanced chiral SHG conversion efficiency (about an order of magnitude greater than the bare aluminum lens) from monolayer tungsten disulfide (WS2)/aluminum metalens, which is designed at the C-exciton resonance of WS2. Since the C-exciton is not a valley exciton, the enhanced chiral SHG in this hybrid system originates from the plasmonic vortex field-enhanced SHG under the optical spin-orbit interaction.
Choice of Optimal Shift Parameter for the Intruder State Removal Techniques in Multireference Perturbation Theory
(2012-11-01)
Chang, Shu-Wei
;
Witek, Henryk A.
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應用化學系
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應用化學系分子科學碩博班
;
Department of Applied Chemistry
An extensive critical evaluation of intruder state removal techniques (aka shift techniques) applicable to multireference perturbation theory (MRPT) shows that the magnitude of the shift parameter a does not influence the spectroscopic parameters of diatomics to a significant degree, provided that the shift is chosen to be sufficiently large. In such case, typical variation of spectroscopic parameters over a wide range of shift parameters is smaller than 0.005 angstrom for equilibrium distances, 30 cm(-1) for harmonic vibrational frequencies, and 0.1 eV for dissociation energies. It is found that large values of a not only remove intruder states but they also bring the MRPT energies and properties closer to experimental values. The presented analysis allows us to determine optimal values of the shift parameters to be used in conjunction with various versions of MRPT; these values are recommended to replace the ad hoc values of sigma suggested in MRPT manuals in calculations for diatomics. Transferability of the optimal shift parameters to larger molecular systems and to other basis sets than aug-cc-pVTZ is anticipated but remains to be formally established.
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.
Cladding Effect on Hybrid Plasmonic Nanowire Cavity at Telecommunication Wavelengths
(2013-05-01)
Cheng, Pi-Ju
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Weng, Chen-Ya
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Chang, Shu-Wei
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Lin, Tzy-Rong
;
Tien, Chung-Hao
In this paper, we investigate the effect of cladding layers on a hybrid plasmonic nanowire cavity. A decent confinement factor and moderate modal loss can be achieved for lasing. Within a certain index range of the cladding layer, the fundamental hybrid plasmonic mode is well confined inside the narrow gain region and becomes the most promising lasing mode. Our results also indicate that the mirror loss can be reduced if the refractive index of the cladding layer is properly chosen. An estimated cold-cavity quality factor of 87, corresponding to a threshold gain of about 1072 cm(-1), is achievable at a cavity length of 10.13 mu m for the lasing mode.
Comparison of wavefront coding optical system using two conjugate phase masks among cubic, sinusoidal, and tangent phase masks
(2017-01-01)
Chen, Shao-Pai
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Cheng, Pi-Ju
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Hsieh, Chi-Ti
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Chang, Shu-Wei
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光電工程學系
Wavefront coding is an effective technique for extending the depth of field. We verified the usefulness of the method of generating symmetrical point spread function by using two conjugate phase masks. According to the results of this study, this method is effective at a small defocus.
Confinement Factors and Modal Volumes of Micro- and Nanocavities Invariant to Integration Regions
(2012-11-01)
Chang, Shu-Wei
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光電工程學系
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Department of Photonics
We present a convenient and self-consistent approach to calculate confinement factors and modal volumes of micro- and nanocavities, which are important for ultrasmall lasers and cavity quantum electrodynamics. This scheme does not rely on the numerical integrations related to optical fields and can avoid the indefinite dependence of physical quantities on integration regions. As a result of this built-in invariance to integration regions, the field representation of the confinement factor, in additional to its conventional expression, contains counter terms of volume and surface integrals, which cancel the effect of arbitrary integration volumes. This procedure is useful for small open cavities or those without sharp boundaries that distinguish cavity regions from free spaces. The uncertainty from different choices of integration regions can be thus eliminated.
Criteria of backscattering in chiral one-way photonic crystals
(2016-01-01)
Cheng, Pi-Ju
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Chang, Shu-Wei
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光電工程學系
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Department of Photonics
Optical isolators are important devices in photonic circuits. To reduce the unwanted reflection in a robust manner, several setups have been realized using nonreciprocal schemes. In this study, we show that the propagating modes in a strongly-guided chiral photonic crystal (no breaking of the reciprocity) are not backscattering-immune even though they are indeed insensitive to many types of scatters. Without the protection from the nonreciprocity, the backscattering occurs under certain circumstances. We present a perturbative method to calculate the backscattering of chiral photonic crystals in the presence of chiral/achiral scatters. The model is, essentially, a simplified analogy to the first-order Born approximation. Under reasonable assumptions based on the behaviors of chiral photonic modes, we obtained the expression of reflection coefficients which provides criteria for the prominent backscattering in such chiral structures. Numerical examinations using the finite-element method were also performed and the results agree well with the theoretical prediction. From both our theory and numerical calculations, we find that the amount of backscattering critically depends on the symmetry of scatter cross sections. Strong reflection takes place when the azimuthal Fourier components of scatter cross sections have an order l of 2. Chiral scatters without these Fourier components would not efficiently reflect the chiral photonic modes. In addition, for these chiral propagating modes, disturbances at the most significant parts of field profiles do not necessarily result in the most effective backscattering. The observation also reveals what types of scatters or defects should be avoided in one-way applications of chiral structures in order to minimize the backscattering.
Current Enhancement and Bipolar Current Modulation of Top-Gate Transistors Based on Monolayer MoS2 on Three-Layer WxMo1-xS2
(2018-07-25)
Chen, Kuan-Chao
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Jian, Cing-Yu
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Chen, Yi-Jia
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Lee, Si-Chen
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Chang, Shu-Wei
We demonstrated the top-gate transistors composed of monolayer MoS2 grown on three-layer alloys MoxW1-xS2 prepared by sequential sulfurization of predeposited transition metal films. The elemental mapping of the alloy indicates a uniform distribution of both cations Mo and W in the grown samples. Surprisingly, we find that the drain current of transistors could be enhanced by 2 orders of magnitude as the composition of Mo increases, whereas the gate-controlled current modulation turns bipolar and ultimately vanishes. These features might originate from the formation of in-gap defect states, with modest activation energy for transport and moderate hopping probability for current conduction, or a reduced electronic band gap of the conducting channel because of strain.
Design of metal-dielectric grating lasers only supporting surface-wave-like modes
(2014-11-17)
Chiang, Po-Jui
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Chang, Shu-Wei
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光電工程學系
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Department of Photonics
We present a prototype of semiconductor lasers with plasmonic periodic structures that only support transverse-magnetic modes at telecommunication wavelengths. The structure does not sustain transverse-electric guided modes which are irrelevant to surface-wave-enhanced applications, and lasing modes must be surface-wave-like. With thin low-index dielectric buffers near the metal surface, the threshold gain is kept at a decent level around the photonic band edge. Thin windows are then opened on the metal surface to let out significant surface fields. This facilitates usages of surface waves for the spectroscopy and sensing. (C) 2014 Optical Society of America
Dressed Linewidth Enhancement Factors in Small Semiconductor Lasers
(2015-11-01)
Chang, Shu-Wei
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光電工程學系
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Department of Photonics
We show that the linewidth of a semiconductor-based small laser, when operated above the threshold, might not directly reflect the permittivity variation induced by carriers in the gain material. In fact, the linewidth may be significantly dressed by responses of modal amplitudes to emitting sources if the small cavity is dispersive, lossy, leaky, spectrally-sharp in gain, but not necessarily intricately-structured. This dressing effect might reduce linewidth enhancements. Despite a large material linewidth enhancement factor, the source-amplitude response could still keep the enhancement effect mild.
Easy Process and Performance Improvement for Top-Emission Organic Light-Emitting Diodes by Using UV Glue as the Insulation Layer on Copper Substrate
(2010-07-01)
Tsai, Yu-Sheng
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Wang, Shun-Hsi
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Juang, Fuh-Shyang
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Chang, Shu-Wei
;
Chen, Chuan-hung
A high heat dissipation material (copper, Cu) was employed as the substrate for top emission organic light-emitting diodes (TEOLEDs). The UV glue was spin-coated onto the Cu substrate as the insulation layer to effectively improve Cu surface roughness and reduce process complexity. From the optoelectronic results, the optimized device with the Cu substrate shows the maximum luminance of 14110 cd/m(2) and luminance efficiency of 7.14 cd/A. The surface and junction temperatures are measured to discuss the heat-dissipating effect on device performance. From the results, TEOLED fabricated on a Cu substrate has lower junction (55.34 degrees C) and surface (25.7 degrees C) temperatures, with the lifetime extended seven times. We employed Cu foil as the substrate for flexible TEOLED with maximum luminance of 10310 cd/m(2) and luminance efficiency of 7.3 cd/A obtained.