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Energy states and magnetization in nanoscale quantum rings
(2002-10-15)
Voskoboynikov, O
;
Li, YM
;
Lu, HM
;
Shih, CF
;
Lee, CP
In this paper we calculate electron energy states and magnetization for torus shaped nanoscale quantum rings with external magnetic fields. We use the three-dimensional effective one-band Hamiltonian, the energy and position-dependent quasiparticle effective mass approximation, and the Ben Daniel-Duke boundary conditions. The dependence of the energy spectrum on the sizes and shapes of the quantum rings was calculated and the result agrees with experimental observations. Penetration of the magnetic field into torus region results in an aperiodic oscillation of magnetization at zero temperature. It saturates with the increasing of the magnetic field strength.
A mixed lubrication model for computer simulation of extrusion processes
(2000-10-01)
Hsu , TC
;
Li, YM
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
A mixed lubrication/friction model for extrusion process is developed in the present research. The model combines a rigid-plasticity finite element code to simulate the interface condition between the tooling and workpiece in the extrusion operation. The influence of surface roughness on lubricant flow is treated by using the average Reynolds equation. The active lubrication regime and appropriate friction factor were determined from the current local values of interface variables such as mean lubricant film thickness and workpiece and tooling roughness, in addition to the more traditional external variables such as interface pressure, node sliding velocity and strain rate of the workpiece. Numerical results using the coupled code include friction stress and normal pressure under different lubrication conditions are compared with experimental investigation. The discrepancy is very small and the proposed model proved to be very efficient in predicting interface friction condition in the extrusion processes.
Energy and coordinate dependent effective mass and confined electron states in quantum dots
(2001)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
友訊交大聯合研發中心
We present a theoretical study of the electron energy states in narrow gap semiconductor quantum dots (QDs). For a finite height hard-wall 3D confinement potential the problem was solved by using of the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, and the Ben Daniel-Duke boundary condition. To solve the 3D Schrodinger equation, we employ a numerical scheme by using the finite difference method and the QR algorithm. Our results show that the parabolic band approximation is applicable only for relatively thin cylindrical QDs or for the dots with large radius. We show that the electron wave function localization plays an important role in the dependency of the energy and the electron effective mass. For the excited states, the non-parabolicity effect has been found to be stronger than it at ground state. (C) 2001 Elsevier Science Ltd. All rights reserved.
Electron energy level calculations for cylindrical narrow gap semiconductor quantum dot
(2001-11-01)
Li, YM
;
Liu, JL
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
Three computational techniques are presented for approximation of the ground state energy and wave function of an electron confined by a disk-shaped InAs quantum dot (QD) embedded in GaAs matrix. The problem is treated with the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, and the Ben-Daniel Duke boundary conditions. To solve the three dimensional (3D) Schrodinger equation, we employ (i) the adiabatic approximation, (ii) the adiabatic approximation with averaging, and (iii) full numerical solution. It is shown that the more efficient approximations (i) and (ii) can only be used for relatively large QD sizes. The full numerical method gives qualitative as well as quantitative trends in electronic properties with various parameters. (C) 2001 Elsevier Science B.V. All rights reserved.
Computer simulation of electron energy levels for different shape InAs/GaAs semiconductor quantum dots
(2001-11-15)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
電子工程學系及電子研究所
A computational technique for the energy levels calculation of an electron confined by a 3D InAs quantum dot (QD) embedded in GaAs semiconductor matrix is presented. Based on the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, a finite height hard-wall 3D confinement potential, and the Ben Daniel-Duke boundary conditions, the problem is formulated and solved for the disk, ellipsoid, and conical-shaped InAs/GaAs QDs. To calculate the ground state and first excited state energy levels, the nonlinear 3D Schrodinger is solved with a developed nonlinear iterative algorithm to obtain the final self-consistent solutions. In the iteration loops, the Schrodinger equation is discretized with a nonuniform mesh finite difference method, and the corresponding matrix eigenvalue problem is solved with the balanced and shifted QR method. The proposed computational method has a monotonically convergent property for all simulation cases. The computed results show that for different quantum dot shapes, the parabolic band approximation is applicable only for relatively large dot volume. For the first excited states the non-parabolicity effect also has been found to be stronger than it at ground state. The QD model and numerical method presented here provide a novel way to calculate the energy levels of QD and it is also useful to clarify principal dependencies of QD energy states on material band parameter and QDs size for various QD shapes. (C) 2001 Elsevier Science B.V. All rights reserved.
A new parallel adaptive finite volume method for the numerical simulation of semiconductor devices
(2001-12-15)
Li, YM
;
Liu, JL
;
Chao, TS
;
Sze, SM
;
應用數學系
Based on adaptive finite volume approximation, a posteriori error estimation, and monotone iteration, a novel system is proposed for parallel simulations of semiconductor devices. The system has two distinct parallel algorithms to perform a complete set of I-V simulations for any specific device model. The first algorithm is a domain decomposition on I-irregular unstructured meshes whereas the second is a parallelization of multiple I-V points. Implemented on a Linux cluster using message passing interface libraries, both algorithms are shown to have excellent balances on dynamic loading and hence result in efficient speedup. Compared with measurement data, computational results of sub-micron MOSFET devices are given to demonstrate the accuracy and efficiency of the system. (C) 2001 Elsevier Science B.V. All rights reserved.
Electron energy state dependence on the shape and size of semiconductor quantum dots
(2001-12-15)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
Tretyak, O
In this article we present a unified model for studying the effect of the sizes and shapes of small semiconductor quantum dots on the electron and hole energy states. We solved the three-dimensional effective one band Schrodinger equation for semiconductor quantum dots with disk, lenticular, and conical shapes. For small InAs/GaAs quantum dots we found a substantial difference in the ground state and first excited state electron energies for dots with the same volume but different shapes. Electron energy dependence on volume is found to be quite different from the commonly quoted V-2/3. The exponent can vary over a wide range and depends on the dot shapes. (C) 2001 American Institute of Physics.
Effect of shape and size on electron transition energies of InAs semiconductor quantum dots
(2002-04-01)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
Tretyak, O
We present a theoretical study of the electron energy states in three-dimensional narrow gap semiconductor quantum (Jots with different shapes under an external magnetic field. The problem is solved by using the effective one-electronic-band Hamiltonian, the energy- and position-dependent electron effective mass approximation and the Ben Daniel-Duke boundary condition. We investigate small InAs/GaAs quantum dots with disk, lenticular, and conical shapes. Electron energy dependence on volume is expressed as V-gamma where the exponent gamma depends on the dot shapes and can vary over a wide range. The most stable against the dot size deviations (among dots of the same base radius) is the energy spectra of the conical dots. In addition, this type of dot also has the weakest diamagnetic shift. Contrarily, quantum dots with cylindrical shapes show a wide deviation in energy and a relatively strong diamagnetic shift.
A domain partition approach to parallel adaptive simulation of dynamic threshold voltage MOSFET
(2002-08-01)
Li, YM
;
Chao, TS
;
Sze, SM
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
In this paper, we present a dynamic domain partition simulation technique for parallel numerical solutions of semiconductor device equations. Based on the adaptive finite volume method, a posteriori error estimation, and monotone iterative algorithm, this dynamic load balancing approach has been successfully developed and implemented on a Linux cluster with message passing interface library. The developed simulator is then applied to calculate the physical characteristics of deep submicron dynamic threshold voltage MOSFET (DTMOS). We simulate DTMOS with two different parallel algorithms: (1) 2D dynamic load balancing for parallel domain decomposition; (2) parallel I-V point simulation. Benchmark results show that a well-designed load balancing simulation can reduce the execution time up to an order of magnitude. Compared with the measured data, the simulated results for a 0.08 mum DTMOS are demonstrated to show the accuracy and efficiency of the method. (C) 2002 Elsevier Science B.V All rights reserved.
Calculation of induced electron states in three-dimensional semiconductor artificial molecules
(2002-08-01)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
友訊交大聯合研發中心
The energy levels calculation of electrons confined in small three-dimensional (3D) coupled quantum InxGa1-xAs dots embedded in GaAs semiconductor matrix is presented. The quantum dots have disk shapes and are separated (in the disk symmetry axis direction) by a certain distance. Based on the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, a finite height hard-wall 3D confinement potential, and the Ben Daniel-Duke boundary conditions, the problem is formulated and solved for the disk-shaped coupled quantum dots. To calculate the ground and induced state energy levels, the nonlinear 3D Schrodinger equation (SE) is solved with a developed nonlinear iterative method to obtain the final self-consistent solutions. In the iteration loops, the Schrodinger equation is discretized with a nonuniform mesh finite difference method, and the matrix eigenvalue problem is solved with the balanced and shifted QR method. Our complete 3D approach demonstrates a principal possibility that the number of bound electronic states in the system can be changed when the interdot (vertical) distance is modified. However, it is impossible to produce an additional possibility to manipulate the system electronic properties within only a two-dimensional (2D) simulation. (C) 2002 Elsevier Science B.V. All rights reserved.

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