Browsing by Author "Lee, Huang-Ming"

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Electronic transport characteristics in a one-dimensional constriction defined by a triple-gate structure
(2006-08-15)
Lee, Huang-Ming
;
Muraki, Koji
;
Chang, Edward Yi
;
Hirayama, Yoshiro
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材料科學與工程學系
We investigate the electronic transport characteristics of a one-dimensional (1D) narrow constriction defined in a GaAs/Al(x)Ga(1-x)As heterostructure by a simple triple-gate structure consisting of a pair of split gates and an additional surface Schottky gate (center gate) between them. Comparison between devices with and without a center gate reveals that the center gate, even when zero biased (V(CG)=0 V), significantly modifies the surface potential and facilitates the 1D confinement in a deep two-dimensional electron system. The pinch-off voltages at V(CG)=0 V for various channel widths W (=0.4-0.8 mu m) and lengths L (=0.2-2 mu m) are well described by the analytical formula based on the pinned-surface model [J. H. Davies , J. Appl. Phys. 77, 4504 (1995)]. Nonlinear transport spectroscopy with an additional dc bias shows that the lowest 1D subband energy separation (Delta E(1,2)) changes linearly with V(CG) and can be enhanced by 70% for V(CG)=0.8 V. A simple model assuming an infinitely long channel and no self-consistent potential well reproduces the overall behavior of the measured Delta E(1,2). In addition, effects of impurities, occasionally found for long-channel devices (L >= 1 mu m), are found to be greatly reduced by applying positive V(CG) and thereby enhancing Delta E(1,2). Data are also presented for the transport anomaly below the first conductance plateau, the so-called "0.7 anomaly," demonstrating that the triple-gate structure is useful for the study of density-dependent phenomena in a 1D system. (c) 2006 American Institute of Physics.
Finite element analysis of antireflective silicon nitride sub-wavelength structures for solar cell applications
(2010-10-01)
Lee, Huang-Ming
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Sahoo, Kartika Chandra
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Li, Yiming
;
Wu, Jong-Ching
;
Chang, Edward Yi
We numerically calculate the spectral reflectivity of the silicon nitride (Si(3)N(4)) sub-wavelength structure (SWS) using a two-dimensional finite element simulation. The geometry-dependent effective reflectance of the Si(3)N(4) SWS over the wavelength ranging from 400 nm to 1000 nm is examined and the structure of Si(3)N(4) SWS is further optimized for the lowest effective reflectance. A p-n junction solar cell efficiency based on the optimized Si(3)N(4) SWS is also calculated, resulting in an improvement of 0.98% in efficiency than that of single layer antireflection coatings. (C) 2010 Elsevier B.V. All rights reserved.
InAlAs/InGaAs metamorphic high electron mobility transistor with Cu/Pt/Ti gate and Cu airbridges
(2007-05-01)
Chang, Chun-Wei
;
Chen, Po-Chou
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Lee, Huang-Ming
;
Chen, Szu-Hung
;
Sahoo, Kartik Chandra
The use of a Cu/Pt/Ti Schottky contact structure and Cu-based airbridges for high-frequency metamorphic high electron mobility transistor (MHEMT) is successfully developed. The material characteristics of the Cu/Pt/Ti Schottky contact on i-InAlAs were studied. Judging from the results of the X-ray diffraction analysis, Auger electron spectroscopy, and transmission electron microscopy, the Cu/Pt/Ti Schottky contact structure on InAlAs was very stable after annealing at 350 degrees C. However, after 400 degrees C annealing, the reaction of copper with the layers underneath started to occur and formed the Cu4Ti phase. The Cu-metallized MHEMT using the proposed Cu/Pt/Ti T-gate structure and Cu-based airbridges has a saturated drain current of 673 mA/mm and a maximum transconductance of 750 mS/mm. The gate to drain breakdown voltage measured was 14.5 V at a gate reverse current of -1 mA/mm. The device also demonstrated a cutoff frequency F-t of 90 GHz and a maximum frequency of oscillation F-max of 165 GHz. An MHEMT with a Au/Pt/Ti gate was fabricated and compared with an MHEMT fabricated with the proposed Cu/Pt/Ti gate. These two kinds of MHEMTs showed similar F-t and F-max. These results demonstrate that the Cu/Pt/Ti T-gate and Cu-based airbridges can be used for MHEMT fabrication with excellent electrical characteristics.
Mechanism of microstructure evolution for the Cu/Ta/GaAs structure after thermal annealing
(2007-04-01)
Chang, Chun-Wei
;
Lee, Huang-Ming
;
Chen, Chang-You
;
Chang, Li
;
Chang, Edward Y.
The diffusion behavior and microstructure evolution of Cu/Ta/GaAs multilayers after thermal annealing are investigated and the mechanism is proposed. A thin 30 nm tantalum layer was sputtered as a diffusion barrier to block Ga and As diffusion into the Cu layer. From the results of sheet resistance measurement, X-ray diffraction analysis, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films on GaAs were found to be very stable up to 500 degrees C without Cu migration into GaAs. After annealing al 550 degrees C, the interfacial mixing of Ta with GaAs substrate occurred, resulting in the formation of TaAs2, and the diffusion of Ga through the Ta layer formed the Cu3Ga phase at the Cu/Ta interface. After annealing at 600 degrees C, the reaction of GaAs with Ta and Cu formed TaAs and Cu3Ga owing to Ga migration and interfacial instability.
Temperature Controlled Perfect Absorber Based on Metal-Superconductor-Metal Square Array
(2012-11-01)
Lee, Huang-Ming
;
Wu, Jong-Ching
;
物理研究所
;
Institute of Physics
The optical properties of a single-band near-perfect absorber are studied numerically by using a finite element method in conjunction with a two-fluid model. Based on a metal-superconductor-metal (MSM) scheme, the proposed structure comprises a lossless superconducting layer sandwiched by a silver square array and ground silver plane. The simulation results clearly show that near-perfect absorption band can be realized and promptly tuned from green light to red light by the temperature of the system. The designed MSM absorber also presents the characteristics of polarization insensitivity and wide-angle incidence up to 50 degree. This prompt manipulation of the near-perfect absorption band makes this MSM absorber a great potential candidate when designing an in-situ absorption band selector in the visible light wavelength regime.
Temperature Controlled Perfect Absorber Based on Metal-Superconductor-Metal Square Array
(2012-11-01)
Lee, Huang-Ming
;
Wu, Jong-Ching
;
物理研究所
;
Institute of Physics
The optical properties of a single-band near-perfect absorber are studied numerically by using a finite element method in conjunction with a two-fluid model. Based on a metal-superconductor-metal (MSM) scheme, the proposed structure comprises a lossless superconducting layer sandwiched by a silver square array and ground silver plane. The simulation results clearly show that near-perfect absorption band can be realized and promptly tuned from green light to red light by the temperature of the system. The designed MSM absorber also presents the characteristics of polarization insensitivity and wide-angle incidence up to 50 degree. This prompt manipulation of the near-perfect absorption band makes this MSM absorber a great potential candidate when designing an in-situ absorption band selector in the visible light wavelength regime.