Browsing by Author "Voskoboynikov, O"

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A computational method for energy level spin splitting simulation in InAs/GaAs semiconductor quantum dots
(2002-05-01)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
Tretyak, O
An impact of the spin-orbit interaction on the electron quantum confinement is considered theoretically for narrow gap semiconductor cylindrical quantum dots. To study the phenomena for InAs quantum dot embedded into GaAs semiconductor matrix, the effective one electronic band Hamiltonian, the energy position dependent electron effective mass approximation, and the spin-dependent Ben Daniel-Duke boundary conditions axe considered, formulated and solved numerically. To solve the nonlinear Schrodinger equation, we propose a nonlinear iterative algorithm. This calculation algorithm not only converges for all simulation cases but also has a good convergent rate. With the developed quantum dot simulator, we study the effect of the spin-orbit interaction for narrow gap InAs/GaAs semiconductor cylindrical quantum dots. From the numerical calculations, it has been observed that the spin-orbit interaction leads to a sizeable spin-splitting of the electron energy states with nonzero angular momentum. Numerical evidence is presented to show the splitting result is strongly dependent on the quantum dot size.
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.
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.
Dependence of energy gap on magnetic field in semiconductor nano-scale quantum rings
(2003-06-10)
Li, YM
;
Lu, HM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
We study the electron and hole energy states for a complete three-dimensional (3D) model of semiconductor nanoscale quantum rings in an external magnetic field. In this study, the model formulation includes: (i) the position dependent effective mass Hamiltonian in non-parabolic approximation for electrons, (ii) the position dependent effective mass Hamiltonian in parabolic approximation for holes, (iii) the finite hard wall confinement potential, and (iv) the Ben Daniel-Duke boundary conditions. To solve this 3D non-linear problem, we apply the non-linear iterative method to obtain self-consistent solutions. We find a non-periodical oscillation of the energy band gap between the lowest electron and hole states as a function of external magnetic fields. The result is useful in describing magneto-optical properties of the nano-scale quantum rings. (C) 2003 Elsevier Science B.V. All rights reserved.
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.
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.
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.
Electron energy state spin-orbit splitting in nanoscopic quantum rings
(2001)
Voskoboynikov, O
;
Huang, HC
;
Shi, C
;
Lee, CP
;
電子工程學系及電子研究所
The impact of spin-orbit interaction on the electron energy states in nanoscopic semiconductor quantum dots and rings is studied theoretically. The effective one-band Hamiltonian approximation with the spin-orbit coupling potential is used. It is shown that the spin-orbit interaction can produce a considerable spin splitting of excited electronic states at zero magnetic fields. We investigated changes in the spin splitting when the geometrical structure is gradually changed from a dot-like shape to a ring-like one. It has been found that the completion of the quantum ring geometry leads to the reversing of the splitting sign. (C) 2001 Elsevier Science Ltd. All rights reserved.
Electron spin filtering in all-semiconductor tunneling structures
(2003-09-01)
Yu, L
;
Huang, HC
;
Voskoboynikov, O
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this work we briefly review the present day perspectives for exploiting conventional nonmagnetic semiconductor nano-technology to design high speed spin-filter devices. In recent theoretical investigations a high spin polarization has been predicted for the ballistic tunneling current in semiconductor single- and double-barrier asymmetric tunnel structures of III-V semiconductors with strong Rashba spin-orbit coupling. We show in this paper that the polarization in the tunneling can probability be sufficiently increased for producing realistic single-barrier structures by including of the Dresselhaus term into consideration. (C) 2004 Published by Elsevier Ltd.
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.
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.
III-V semiconductor nano-rings
(2004-08-01)
Lee, BC
;
Voskoboynikov, O
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this work, we briefly review present day knowledge about possible types, methods of fabrication, and fascination physical properties of nano-scale semiconductor rings. In particular, we discuss models of the ring formation, energetic, magnetic, and magneto-optical properties of InAs/GaAs and InAs/InP nano-rings as well as GaAs/GaSb "open nanorings". In addition, we summarize results of realistic theoretical -simulations of the electronic energy spectra, magnetic and optical properties for totally three-dimensional models of nano-scale quantum rings. (C) 2004 Elsevier B.V. All rights reserved.
Interband magneto-optical transitions in a layer of semiconductor nano-rings
(2005-06-01)
Voskoboynikov, O
;
Wijers, CMJ
;
Liu, JL
;
Lee, CP
;
應用數學系
We have developed a quantitative theory of the collective electromagnetic response of layers of semiconductor nano-rings. The response can be controlled by means of an applied magnetic field through the optical Aharonov-Bohm effect and is ultimately required for the design of composite materials. We demonstrate that the local field is of paramount importance in the description of such layers. The changes in ellipsometric parameters are 2 to 3 orders of magnitude above the detection limit of a modern ellipsometer.
Left handed composite materials in the optical range
(2005-03-01)
Voskoboynikov, O
;
Dyankov, G
;
Wijers, CMJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The purpose of this paper is to show that semiconductor nano-structures built from non-magnetic InAs/GaAs nano-rings can exhibit simultaneously negative effective permittivity and permeability over a certain optical frequency range. The structures are resonant and have this property near the edge of absorption of the nano-rings. This can be particularly interesting in the investigation of the challenging problem of development of left-handed composite materials in the optical range. (c) 2005 Elsevier Ltd. All rights reserved.
Magnetic properties of parabolic quantum dots in the presence of the spin-orbit interaction
(2003-11-01)
Voskoboynikov, O
;
Bauga, O
;
Lee, CP
;
Tretyak, O
;
交大名義發表
We present a theoretical study of the effect of the spin-orbit interaction on the electron magnetization and magnetic susceptibility of small semiconductor quantum dots. Those characteristics demonstrate quite interesting behavior at low temperature. The abrupt changes of the magnetization and susceptibility at low magnetic fields are attributed to the alternative crossing between the spin-split electron levels in the energy spectrum, essentially due to the spin-orbit interaction (an analog of the general Paschen-Back effect). Detailed calculation using parameters of InAs semiconductor quantum dot demonstrates an enhancement of paramagnetism of the dots. There is an additional possibility to control the effect by external electric fields or the dot design. (C) 2003 American Institute of Physics.
Magnetization and magnetic susceptibility of InAs nano-rings
(2004-01-01)
Voskoboynikov, O
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this work, we investigate theoretically the magnetic susceptibility of the three-dimensional cut-torus-shaped quantum rings. The calculations are carried out for the realistic three-dimensional model of InAs/GaAs nano-rings with the hard-wall confinement potential, three-dimensional effective one-electronic-band Hamiltonian with position and energy-dependent effective mass, and Ben Daniel-Duke boundary conditions. This allows us to describe the penetration of the magnetic field into the torus region. At zero temperature, the ring's differential susceptibility demonstrates delta-like paramagnetic peaks, which are generated by aperiodic oscillations of magnetization. With increasing temperature, the peaks gradually transform into Lorenz-shaped peaks and then disappear. As opposed to meso-scopic quantum rings we found a dependence of the peak's amplitude on the dimensions of the rings. (C) 2003 Elsevier B.V. All rights reserved.
Magneto-optical response of layers of semiconductor quantum dots and nanorings
(2005-06-01)
Voskoboynikov, O
;
Wijers, CMJ
;
Liu, JL
;
Lee, CP
;
應用數學系
In this paper a comparative theoretical study was made of the magneto-optical response of square lattices of nanoobjects (dots and rings). Expressions for both the polarizability of the individual objects as their mutual electromagnetic interactions (for a lattice in vacuum) was derived. The quantum-mechanical part of the derivation is based upon the commonly used envelope function approximation. The description is suited to investigate the optical response of these layers in a narrow region near the interband transitions onset, particularly when the contribution of individual level pairs can be separately observed. A remarkable distinction between clearly quantum-mechanical and classical electromagnetic behavior was found in the shape and volume dependence of the polarizability of the dots and rings. This optical response of a single plane of quantum dots and nanorings was explored as a function of frequency, magnetic field, and angle of incidence. Although the reflectance of these layer systems is not very strong, the ellipsometric angles are large. For these isolated dot-ring systems they are of the order of magnitude of degrees. For the ring systems a full oscillation of the optical Bohm-Ahronov effect could be isolated. Layers of dots do not display any remarkable magnetic field dependence. Both type of systems, dots and rings, exhibit an outspoken angular-dependent dichroism of quantum-mechanical origin.
Magneto-optics of layers of semiconductor quantum dots and nano-rings
(2006-06-01)
Voskoboynikov, O
;
Wijers, CMJ
;
Liu, JL
;
Lee, CP
;
交大名義發表
We have studied the collective magneto-optical response of layers of semiconductor quantum dots and nanorings. Expressions for both the polarizability of the individual nano-objects have been used to determine the magneto-optical response on square two-dimensional lattices on those nano-objects as a function on frequency, magnetic field and angle of incidence. The magnetic field dependence of the response for layers of rings gives rise to the Aharonov-Bohm type oscillatory behavior in the reflectance and absorbance that can be measurable. Layers of dots do not display any remarkable magnetic field dependence.
Role of the spin-orbit interaction in elastic scattering of electrons in quantum wells
(2003-05-01)
Huang, HC
;
Voskoboynikov, O
;
Lee, CP
;
交大名義發表
;
National Chiao Tung University
We present a theoretical study of the spin-dependent electron scattering from screened impurities in Ill-V semiconductor quantum wells. The effective one band Hamiltonian and the Rashba spin-orbit interaction are used. We calculated the Mott scattering cross-section and the Sherman function for two-dimensional electrons spin-polarized parallel to the z-axis (direction of structure growth). We have found a large spin-dependent asymmetry in the elastic cross-section for electrons scattered from impurities in CdTe/InSb/CdTe symmetrical semiconductor quantum wells. The Sherman function amplitude for repulsive impurities in CdTe/InSb/CdTe quantum wells is predicted to be about 0.01. (C) 2003 Elsevier Science Ltd. All rights reserved.
Slow light in photonic crystals
(2005-03-01)
Chu, JH
;
Voskoboynikov, O
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this work we demonstrate an interesting opportunity to decrease drastically the group velocity of light in two-dimensional photonic crystals constructed form materials with large dielectric constant without dispersion (epsilon(d) similar to 100). The group velocity of light in the crystals can be lowered up to 10(-5) - 10(-4) c (c is velocity of light in free space) in a wide range of the Brillouin zone. We propose a simple and general explanation why that should appear in photonic crystals with large dielectric constants. (c) 2005 Elsevier Ltd. All rights reserved.