Browsing by Author "Lin, Chia-Hsien"

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A Microstrip-fed Circularly-Polarized Loop-like Antenna
(2009)
Lin, Chia-Hsien
;
Wu, Jin-Wei
;
Chiou, Tong-Chia
;
Chen, Chih-Hsing
;
Wang, Chien-Jen
A microstrip-fed loop-like antenna designs with circular polarization (CP) is presented in this paper. The proposed loop-like antenna comprised of a monopole antenna, a sleeve strip connected with the ground plane and an L-shaped slit embedded in the ground plane. The C-like monopole generates a resonant mode for wideband impedance-bandwidth at the GPS and DCS bands, and the sleeve and the slit are capable of exciting two orthogonal electric fields with equal amplitude and phase difference of 90 degree for radiating circular polarization at 1.575 GHz. Both simulated and measured results are provided to validate the CP performance of the proposed antenna.
Anticorrelation between the splitting and polarization of the exciton fine structure in single self-assembled InAs/GaAs quantum dots
(2011-02-28)
Lin, Chia-Hsien
;
You, Wen-Ting
;
Chou, Hsiang-Yu
;
Cheng, Shun-Jen
;
Lin, Sheng-Di
We report on a systematic correlation between the fine-structure splitting and polarization anisotropy of excitons in InAs/GaAs quantum dots, but with an unexpected reversal in order of the polarization eigenaxes. Such an anticorrelation is explained by a large valence-band-mixing induced splitting due to the shape and strain anisotropies. The strength and phase of valence band mixing are also found to play an important role in the tuning of fine structure splitting using an in-plane magnetic field.
Compact Coplanar-waveguide Band-rejection DGS Resonators
(2010)
Sun, De-Liang
;
Wang, Chien-Jen
;
Lin, Chia-Hsien
;
Tsai, Yi-Che
;
電機工程學系
In this paper, compact coplanar-waveguide (CPW) defected-ground-structure (DGS) resonators are demonstrated, by placing floating patches. Two T-shaped slots as a bandstop resonator are etched in two ground planes of a CPW 50 Omega transmission line. Two rectangular patches are symmetrically placed on the bottom layer of the substrate. The patches modeled as an additional capacitance increase the effective capacitance of the resonator. By tuning the geometrical dimension of the patches, the resonance frequency is lowered.
Diamagnetic Response of Exciton Complexes in Semiconductor Quantum Dots
(2008-12-31)
Tsai, Ming-Fu
;
Lin, Hsuan
;
Lin, Chia-Hsien
;
Lin, Sheng-Di
;
Wang, Sheng-Yun
We report measurements of diamagnetic shifts for different exciton complexes confined in small InAs quantum dots. The measured diamagnetic responses are sensitive to the number of carriers in the exciton complexes, with systematic differences between neutral excitons, biexcitons, and trions. Theoretical calculations suggest that such systematic differences arise from very different extents of electron and hole wave functions confined in small quantum dots. The measured magnetic response of Coulomb energies is found to vary with the cube of the wave function extent, and can be a sensitive probe to the electron-hole wave function asymmetry.
Electron-hole symmetry breakings in optical fine structures of single self-assembled quantum dots
(2010-02-01)
Ramirez, Hanz Y.
;
Lin, Chia-Hsien
;
You, Wen Ting
;
Huang, Shan-Yu
;
Chang, Wen-Hao
The effects of electron-hole (e-h) symmetry breaking on the optical fine structure splitting (FSS) of single excitons in individual InGaAs/GaAs self-assembled quantum dots are experimentally and theoretically studied. The measured FSSs of small InGaAs/GaAs self-assembled quantum dots show a monotonic decrease wills increasing emission energy and eventually almost vanish (<= 10 mu eV) in the high energy regime. A theory based on 3D asymmetric parabolic model for e-h exchange interaction in combination with 3D finite difference simulations for Ga-diffused InGaAs/GaAs QDs is developed to explore the underlying physics. The reduced FSSs in the high emission energy regime are shown closely related to the e-h wave function symmetry breaking which is especially significant in highly Ga-diffused quantum dots. The Ga-diffusion induced e-h asymmetry reduces the e-h wave function overlap and results in the feature of reduced fine energy splitting. (c) 2009 Elsevier Boy. All rights reserved.
Electron-hole symmetry breakings in optical fine structures of single self-assembled quantum dots (vol 42, pg 1155, 2010)
(2010-11-01)
Ramirez, Hanz Y.
;
Lin, Chia-Hsien
;
You, Wen Ting
;
Huang, Shan-Yu
;
Chang, Wen-Hao
Electron-hole symmetry breakings in optical fine structures of single self-assembled quantum dots (vol 42, pg 1155, 2010)
(2010-11-01)
Ramirez, Hanz Y.
;
Lin, Chia-Hsien
;
You, Wen Ting
;
Huang, Shan-Yu
;
Chang, Wen-Hao
Exciton fine structures and energy transfer in single InGaAs quantum-dot molecules
(2009)
Lin, Hsuan
;
Wang, Sheng-Yun
;
Lin, Chia-Hsien
;
Chang, Wen-Hao
;
Cheng, Shun-Jen
We present a spectroscopic study of single quantum-dot molecules (QDMs) formed by two closely stacked In(0.5)Ga(0.5)As/GaAs layers. It was found that the interdot coupling and directional energy transfer between the two adjacent dots can be controlled by temperature tuning. Direct and indirect excitons, as well as charged excitons in single QDMs were classified and identified by excitation-power dependent, excitation-energy dependent and polarization-resolved microphotoluminescence measurements. With the increasing temperature, the direct-exciton intensity decreases while the indirect-exciton intensity increases. A rate equation model considering phonon mediated processes has been developed. The directional energy transfer in QDMs is explained in terms of the phonon-assisted tunnelling of hole between the two adjacent dots. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Impacts of Coulomb Interactions on the Magnetic Responses of Excitonic Complexes in Single Semiconductor Nanostructures
(2010-04-01)
Chang, Wen-Hao
;
Lin, Chia-Hsien
;
Fu, Ying-Jhe
;
Lin, Ta-Chun
;
Lin, Hsuan
We report on the diamagnetic responses of different exciton complexes in single InAs/GaAs self-assembled quantum dots (QDs) and quantum rings (QRs). For QDs, the imbalanced magnetic responses of inter-particle Coulomb interactions play a crucial role in the diamagnetic shifts of excitons (X), biexcitons (XX), and positive trions (X (-) ). For negative trions (X (-) ) in QDs, anomalous magnetic responses are observed, which cannot be described by the conventional quadratic energy shift with the magnetic field. The anomalous behavior is attributed to the apparent change in the electron wave function extent after photon emission due to the strong Coulomb attraction by the hole in its initial state. In QRs, the diamagnetic responses of X and XX also show different behaviors. Unlike QDs, the diamagnetic shift of XX in QRs is considerably larger than that of X. The inherent structural asymmetry combined with the inter-particle Coulomb interactions makes the wave function distribution of XX very different from that of X in QRs. Our results suggest that the phase coherence of XX in QRs may survive from the wave function localization due to the structural asymmetry or imperfections.
Impacts of structural asymmetry on the magnetic response of excitons and biexcitons in single self-assembled In(Ga)As quantum rings
(2009-08-01)
Lin, Ta-Chun
;
Lin, Chia-Hsien
;
Ling, Hong-Shi
;
Fu, Ying-Jhe
;
Chang, Wen-Hao
The diamagnetic shifts of neutral excitons and biexcitons confined in single self-assembled In(Ga)As/GaAs quantum rings are investigated. Unlike quantum dots, quantum rings reveal a considerably large biexciton diamagnetic shift, about two times larger than that of single excitons. Based on model calculations, we found that the inherent structural asymmetry and imperfection, combined with the interparticle Coulomb interactions, is the fundamental cause of the more extended biexciton wave function in the quantum rings. The exciton wave function tends to be localized in one of the potential valleys induced by structural imperfections of the quantum ring due to the strong localization of hole and the electron-hole Coulomb attraction, resembling the behavior in single dots. Our results suggest that the phase coherence of neutral excitons in quantum rings will be smeared out by such wave function localizations.
Multi-scale mapping for collagen-regulated mineralization in bone remodeling of additive manufacturing porous implants
(2019-05-15)
Tsai, Pei-I.
;
Lam, Tu-Ngoc
;
Wu, Meng-Huang
;
Tseng, Kuan-Ying
;
Chang, Yuan-Wei
Long term success of metallic fusion cages depends on mechanobiological processes through the bone incorporation and rich osseointegration. An optimal configuration of porous titanium-aluminum-vanadium (Ti-6Al-4V) implant fabricated via the additive manufacturing was evaluated in complimentary structure examinations to investigate the growth of autologous osseous at multi-length scales. X-ray microcomputed tomography (micro-CT) and transmission X-ray microscopy (TXM) using newly-built analysis method indicate the porous Ti-6Al-4V is much better for bone ingrowth compared to commercially non-porous titanium (Ti) and porous tantalum (Ta) implants at the ultramicrostructural level. The evolution of bone formation and remodeling acquired by nano X-ray Laue diffraction mapping exhibits the isotropic orientation and low crystallinity of all newly formed bone whereas mature bone in Ti-6Al-4V discloses the preferential alignment and higher crystallinity volumes of constituent hydroxyapatite (HA) crystallites. The high degree in mineral crystallinity of the fully mature bone suggests additive manufactured Ti-6Al-4V pores enhance the collagen-regulated mineralization.
Nonresonant carrier transfer in single InGaAs/GaAs quantum dot molecules
(2008-06-01)
Chang, Wen-Hao
;
Lin, Hsuan
;
Wang, Sheng-Yun
;
Lin, Chia-Hsien
;
Cheng, Shun-Jen
We present a spectroscopic study of single quantum dot molecules (QDMs) formed by two closely stacked In(0.5)Ga(0.5)As layers. The exciton fine structures as well as direct and indirect excitonic species associated with QDMs were identified by power dependent and polarization resolved microphotoluminescence measurements. As the temperature was increased, a directional energy transfer between the direct and indirect excitons in single QDMs was observed. A rate-equation model was developed to explain our data. We show that a phonon-assisted nonresonant tunneling of the hole between the two adjacent dots is responsible for such directional energy transfers in QDMs.
Stress tuning of strong and weak couplings between quantum dots and cavity modes in microdisk microcavities
(2011-11-01)
Lin, Hsuan
;
Lin, Chia-Hsien
;
Lai, Wei-Chen
;
Lee, Yi-Shan
;
Lin, Sheng-Di
We present the control of couplings between quantum dots and cavity modes in microdisk microcavities by a stress tuning scheme. The excitonic transitions and cavity modes can be brought into resonance due to their different energy shift rates with the applied strain. Spectral signatures of both strong and weak couplings are clearly observed. The strain tunable device can be used to tune the exciton wavelength bidirectionally at constant temperatures without significantly affecting the emission rate and linewidth of excitons.
Suppressed piezoelectric polarization in single InGaN/GaN heterostructure nanowires
(2013-10-28)
Tsai, Wen-Che
;
Chen, Yen-Ting
;
Lin, Chia-Hsien
;
Hsu, Wei-Ting
;
Hsu, Yung-Sheng
The optical properties of single InGaN/GaN heterostructure nanowires (NWs) with a mean diameter down to 18 nm are investigated. Sharp emission lines originating from the recombination of localized excitons in the InGaN disk layer can be resolved. Excitation-dependent energy shifts, together with spectral diffusions of these emission lines, indicate the presence of a weak quantum confined Stark effect (QCSE) caused by nearby charge fluctuations, rather than the screening of piezoelectric polarizations at the InGaN/GaN interface. The absence of a piezoelectric polarization field is further confirmed by time-resolved photoluminescence measurements. Numerical simulations reveal that the elastic strain relaxation via the NW geometry is marginal and occurs only near the NW sidewalls. Carrier localization preferentially near the periphery of the InGaN disk and alloy intermixing are suggested as possible reasons for the absence of a polarization-induced QCSE in thin InGaN/GaN heterostructure NWs.