Browsing by Author "Huang, YS"

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Analysis of size distributions of type IIZnTe/ZnSe quantum dots
(2004-12-01)
Lee, J
;
Yang, CS
;
Chang, CT
;
Liu, JR
;
Chou, WC
The photoluminescence (PL) spectrum of the ZnTe/ZnSe quantum dot (QD) structure which has a type II band alignment. was investigated. A broader structure peaking at 2.180 eV together with the features of the ZnSe buffer layer located at 2.820 eV in the PL spectrum at 10 K were observed. The broadness of the PL attributes to the spatial inhomogeneity of the QD sizes. The PL spectrum was a normal distribution with a variance of 0.002 eV(2). However, the dot size distribution was a deformed Gaussian. Using only one set of data of dot size distribution measured by the Atomic Force Microscopy (AFM), the statistical estimates with standard errors were evaluated using the bootstrap methodology. The probability distribution was inferred by calculating the means, percentiles and correlation coefficients of the base diameter and the height of the QDs. We concluded that the dot distributions were indeed a deformed Gaussian and the correlation coefficient of the diameter and the height of the QDs was 0.49 +/- 0.01. The uniformity of the dot size distribution was poor. To infer the dot size distribution from the PL spectrum, we numerically solved the Schrodinger equation by elaborating on the orthogonal periodic functions (OPF) approximation for the type II lens shaped QDs. The convergence of the probability density was discussed in a great detail. We found that the band edge discontinuities inside the dot acts as a barrier with DeltaE(v) = 315 meV for the conduction band and as a well with DeltaE(v) = 735 meV for the valence band. In the AFM measurement, the offset in dot height is 14 Angstrom and the aspect ratio is 0.04. We employed the Schrodinger equation to correlated the PL spectrum (intensity versus optical energy) to the AFM data (number of QDs versus dot size) and the agreement was excellent. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Cell-based dual snake model: A new approach to extracting highly winding boundaries in the ultrasound images
(2002-08-01)
Chen, CM
;
Lu, HHS
;
Huang, YS
;
統計學研究所
;
Institute of Statistics
Two common deficiencies of most conventional deformable models are the need to place the initial contour very close to the desired boundary and the incapability of capturing a highly winding boundary for sonographic boundary extraction. To remedy these two deficiencies, a new deformable model (namely, the cell-based dual snake model) is proposed in this paper. The basic idea is to apply the dual snake model in the cell-based deformation manner. While the dual snake model provides an effective mechanism allowing a distant initial contour, the cell-based deformation makes it possible to catch the winding characteristics of the desired boundary. The performance of the proposed cell-based dual snake model has been evaluated on synthetic images with simulated speckles and on the clinical ultrasound (US) images. The experimental results show that the mean distances from the derived to the desired boundary points are 0.9 +/- 0.42 pixels and 1.29 +/- 0.39 pixels for the synthetic and the clinical US images, respectively.
Confined hydrogen in uniform electric field
(2000-08-10)
Huang, YS
;
Liaw, SS
;
電子物理學系
;
Department of Electrophysics
We calculate the resonant energies and linewidths of hydrogen bounded by a parabolic cavity and exposed to an external uniform electric field. Energies and widths oscillate as a function of the size of the cavity. This interesting property differs from the previous result for the case of spherical cavity without the external field.
Electron-electron scattering times in low-diffusivity thick RuO2 and IrO2 films
(1999-01-01)
Lin, JJ
;
Xu, W
;
Zhong, YL
;
Huang, JH
;
Huang, YS
We have systematically measured the electron dephasing scattering times from a three-dimensional weak-localization study of low-diffusivity thick RuO2 and IrO2 films. We find that the inelastic electron scattering rate 1/tau(in) varies essentially Linearly with the temperature and there is essentially no dependence of 1/tau(in) on the electron elastic mean free path. This observation is understood in terms of the current theoretical concept for electron-electron scattering in strongly disordered bulk conductors. [S0163-1829(99)02601-6].
Level stability of the quantum dots with impurity
(1999-11-20)
Huang, YS
;
Liaw, SS
;
電子物理學系
;
Department of Electrophysics
An atom located at the center of the constant spherical potential is adopted as a simple model for a quantum dot with impurity. We find that, under this model, the stability of the energy levels of a quantum dot with impurity can be controlled by adjusting either the size or the band gap of the quantum dot.
Low temperature electrical transport properties of RuO2 and IrO2 single crystals
(2004-11-17)
Lin, JJ
;
Huang, SM
;
Lin, YH
;
Lee, TC
;
Liu, H
We have systematically measured the electrical transport properties of several RuO2 and IrO2 single crystals over a wide temperature range from 300 K down to 0.3 K to study the conduction mechanisms in these oxides. Our measured resistivities are in close agreement with the recent band-theory calculations for these materials. The characteristic temperatures for the acoustic-mode and optical-mode phonons are determined. Our measured magnetoresistances are positive and follow the Kohler rule, indicating that the transport properties of these oxides exhibit normal behaviour as described by the Boltzmann equation. In contrast, we do not find any signature of superconductivity down to 0.3 K, though the band-theory calculations predict a superconducting transition temperature of similar to5 K. Magnetization measurements suggest a very low level of paramagnetic impurities in our crystals.
Optical absorption coefficient of quantum wires in strain and electric fields with intermixing interfaces
(2005-09-01)
Lee, J
;
Spector, HN
;
Chou, WC
;
Huang, YS
;
電子物理學系
We have theoretically studied the optical absorption coefficient of quantum wires in electric and strain fields with intermixing interfaces. The potential profiles are governed by the intermixing heterojunctions, internal strain due to the lattice mismatch, the external electric field and stress. The second Fick's law describes the wires' intermixing heterojunctions due to the alloy interdiffusion. We adopt the Green's function method to solve the Poisson equation for the displacement to determine the internal strain due to the lattice mismatch. The single-band Schrodinger equation in the effective mass approximation is used to describe the conduction subband structures while the four-band Kohn-Luttinger Hamiltonian is used to describe the valence subband structures. In solving the Schrodinger equation and the Kohn-Luttinger Hamiltonian, we expand the wave functions for the electrons and holes by using linear combinations of the two-dimensional harmonic oscillator wave functions to yield two matrix equations. These matrix equations are numerically solved for their eigen-energies and their corresponding eigenfunctions. We investigate some physical properties of the unstrained quantum wire (GaAs/AlAs) and the strained wire (CdSe/ZnSe) as examples. When the interdiffusion becomes stronger, on one hand, the internal strain is relaxed leading to the band gap shrinkage (if the initial strain epsilon(0)< 0) and, on the other hand, the potential profiles are deformed and the effective band gap becomes wider. Variations of the transition energies with external stress show the anticrossing effect and variations of the transition energies with external electric field show the field emission effect. The hole effective masses can be enhanced or become electronlike by applying stress to the wire. The oscillator strengths of the dipole-allowed intersubband transitions for the y and z polarizations are calculated to infer possible optical transitions. The optical absorption coefficients together with the joint density of states are calculated.
The energy spectrum of parabolic quantum dots
(2000-12-18)
Yang, CC
;
Huang, YS
;
電子物理學系
;
Department of Electrophysics
We calculate the energy spectrum of hydrogen impurity located in the center of parabolic quantum dot. The energy levels under this model differ from the previous results for the case of spherical quantum dot. The degeneracy of the energy levels is quite different as well. However, compared with the spherical quantum dot, the energy plateau under this model is not obvious. (C) 2000 Elsevier Science B.V. All rights reserved.