Browsing by Author "Voskoboynikov, O."

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A hybrid model for the magneto-optics of embedded nano-objects
(2006)
Wijers, C. M. J.
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Voskoboynikov, O.
;
Liu, J. L.
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The influence of the surrounding semiconducting matrix upon the polarizability of embedded nano-objects (nano-rings) has been investigated using a hybrid discrete/continuum model. It describes embedded systems by excess discrete dipoles with excess polarizability against a uniform background with the host material dielectric constant. The polarizability combines the static polarizability of an ellipsoidal ring with a dynamic quantum mechanical frequency dependent term. The result of the model for the particular nano-ring host combination investigated is an increased internal reflectance and an overall strong increment of the structure in reflectance/ellipsometric angles, displaying clearly the optical Aharonov-Bohm effect. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
A model for semiconductor quantum dot molecule based on the current spin density functional theory
(2006-11-01)
Liu, Jinn-Liang
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Chen, Jen-Hao
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Voskoboynikov, O.
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應用數學系
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電子工程學系及電子研究所
Based on the current spin density functional theory, a theoretical model of three vertically aligned semiconductor quantum dots is proposed and numerically studied. This quantum dot molecule (QDM) model is treated with realistic hard-wall confinement potential and external magnetic field in three-dimensional setting. Using the effective-mass approximation with band nonparabolicity, the many-body Hamiltonian results in a cubic eigenvalue problem from a finite difference discretization. A self-consistent algorithm for solving the Schrodinger-Poisson system by using the Jacobi-Davidson method and GMRES is given to illustrate the Kohn-Sham orbitals and energies of six electrons in the molecule with some magnetic fields. It is shown that the six electrons residing in the central dot at zero magnetic field can be changed to such that each dot contains two electrons with some feasible magnetic field. The Forster-Dexter resonant energy transfer may therefore be generated by two individual QDMs. This may motivate a new paradigm of Fermionic qubits for quantum computing in solid-state systems. (C) 2006 Elsevier B.V. All rights reserved.
Binding energy of magneto-biexcitons in semiconductor nano-rings
(2010)
Thu, L. M.
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Chiu, W. T.
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Xue, Shao-Fu
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Lin, Ta-Chun
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Voskoboynikov, O.
We report a simulation on the magneto-biexciton system of asymmetrical InAs/GaAs nano-rings, using a smooth three dimensional confinement potential which realistically describes electronic properties of the rings. In our calculation, we use the Hartree approximation to calculate the self-consistent energy for exciton and biexciton confined in the system. We simulate recombination energy, binding energy and their diamagnetic shifts and compare those results with experimental data obtained from the magneto-photoluminescence measurement. We found that using the realistic geometry and composition of the asymmetric nano-ring in our simulations we are able to reproduce experimental data with good accuracy.
Computer simulation of the non-uniform and anisotropic diamagnetic shift of electronic energy levels in double quantum dot molecules
(2010-10-01)
Thu, L. M.
;
Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this study we calculated the lowest energy states of electrons confined in an asymmetrical InAs/GaAs double lens-shaped quantum dot molecule in external magnetic field. Based on the effective three-dimensional one electronic-band Hamiltonian approximation (with the energy and position dependent electronic effective mass) the electronic energy states of the system were computed by non-linear iterative method using Comsol MultiPhysics package. Our description allows us to simulate the semiconductor quantum dot molecule in arbitrary directed magnetic field. Simulation results clearly show that the diamagnetic shifts of the electronic energy levels are anisotropic and non-uniform. Therefore we demonstrate an opportunity to dynamically manipulate electronic states not only by varying the magnitude but also changing the direction of the magnetic field. (C) 2010 Elsevier B. V. All rights reserved.
Effect of geometry on the excitonic diamagnetic shift of nano-rings
(2011)
Thu, L. M.
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Chiu, W. T.
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Lin, Ta-Chun
;
Voskoboynikov, O.
;
電子工程學系及電子研究所
We simulate magneto-excitons confined in asymmetrically wobbled three-dimensional InAs/GaAs nano-rings. The wobbling asymmetry reproduces realistic experimental geometry of the rings and generates an asymmetry in the side valleys of the three dimensional confinement potential. Using our mapping method and the exact diagonization approach we calculated the excitonic diamagnetic shift and found that even a small wobbling asymmetry can drastically change the diamagnetic shift coefficient. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Effect of size and shape dispersion on the averaged magnetic response of ensembles of semiconductor quantum rings
(2012-05-11)
Thu, L. M.
;
Chiu, W. T.
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Voskoboynikov, O.
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper a theoretical study was made of the conditional averages of the magnetization and magnetic susceptibility of dispersive ensembles of nano-objects with a very complex geometry-self-assembled wobbled semiconductor quantum rings. Using the multivariate statistics approach and previously proposed mapping method the impact of the dispersion of the ring geometry parameters on the static magnetic response of the ensembles has been investigated near the first Aharonov-Bohm oscillation. The description is suited to clarify the important question of which geometrical parameters' dispersions are crucial for the formation and properties of the magnetic response of ensembles. We theoretically show that for the dispersive ensembles of InGaAs/GaAs capped wobbled quantum rings the actual value and temperature dependence of the differential magnetic susceptibility can be optimized by an appropriate control of the conditional parameters of the ensembles. The ring rim radius variations play a crucial role in this dependence. We have managed to simulate in detail the temperature behavior of the meaningful averages of the magnetization and positive peak of the differential magnetic susceptibility for ensembles of the rings known from the experiment. The simulated temperature dependence, position, and magnitude of the positive peak in the differential magnetic susceptibility are in a good agreement with the experimental observations.
Effects of geometrical shape dispersion on inhomogeneous broadening of excitonic peaks of semiconductor nano-objects
(2011-03-14)
Thu, L. M.
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Chiu, W. T.
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Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We present an efficient method for simulation of the inhomogeneous broadening of photoluminescence peaks of dispersive ensembles of semiconductor nano-objects. Using our mapping method for geometrical and material parameters of the objects, we managed to connect the position, asymmetry, and width of the photoluminescence emission peaks of ensembles of the objects to the actual dispersion of the geometrical shapes of the objects. The mapping method allows us to very efficiently reproduce and explain experimental data on the photoluminescence of dispersive ensembles of triple concentric GaAs/AlGaAs nano-rings, i.e., nano-objects with a very sophisticated three-dimensional geometry.
Electromagnetic Response of Three-Dimensional Arrays of Quantum Dot Molecules
(2011)
Thu, L. M.
;
Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We theoretically study the impact of the coherent manipulation of electronic states in double vertical lens-shaped circular InAs/GaAs quantum dot molecules on the collective optical characteristics (effective permittivity) of three-dimensional arrays of those nano-objects. For the asymmetric molecules we demonstrate an opportunity to drive the effective permittivity by applying an external magnetic field to the arrays. We show that one can observe the changes in the quantum mechanical states of the molecules by monitoring changes of the effective permittivity of arrays of such nano-objects.
Magnetic Qubit in a Non-Magnetic Semiconductor Quantum Dot Molecule
(2010-09-01)
Voskoboynikov, O.
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Wijers, C. M. J.
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交大名義發表
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National Chiao Tung University
We consider a system of two vertical lens-shaped circular InAs/GaAs quantum dots when an external magnetic field is applied along the system's growth direction. The quantum dots have substantially different diameters in contrast to most of the known systems. We discuss a possibility to coherently drive coupled electronic ground states (to relocate electronic wave functions from one dot to another). This can be described as a manipulation of a magnetic iso-spin qubit. At the same time the relocation correlates with the anti-crossing behavior of the two lowest electronic states of the quantum dot molecule and generates unusual features of the magnetic susceptibility of the system. It follows from this theoretical study that in our non-magnetic system we can perform and monitor the magnetic qubit. The qubit can be dynamically driven by an external magnetic field and retraced from the magnetic susceptibility changes. A few single-qubit quantum gates can be performed.
Magneto-optics of layers of double quantum dot molecules
(2009-10-01)
Thu, L. M.
;
Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We present a general treatment of the magneto-optical response from systems of semiconductor nano objects of arbitrary shapes. Our theoretical hybrid method allows us to simulate the coherent manipulation of the quantum states of electrons and holes in nano objects and monitor that by means of analysis of the collective magneto-optical response from the system. As an example of the method implementation we consider the coherent manipulation of the electronic states of a asymmetrical double InAs quantum dot molecule embedded in GaAs matrix and the collective magneto-optical properties of a layer of the molecules. Our simulation results show that changes in the quantum-mechanical configuration of the quantum dot molecules can be observable by monitoring changes in the ellipsometric data obtained for layers made from these nano objects. The ellipsometric data clearly represent the quantum mechanics of the molecules.
Magneto-optics of two dimensional arrays of semiconductor quantum dot molecules
(2010-02-01)
Thu, L. M.
;
Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We theoretically study an impact of the coherent manipulation of electronic states in an asymmetrical double InAs/GaAs quantum dot molecule on the magneto-optical response from two dimensional arrays of those nano-objects. The quantum dot molecules are modeled within complete three-dimensional description that allows us to simulate arbitrary directions of external magnetic field. We demonstrate a possibility to reconfigure electronic wave functions within the molecule by applying external magnetic field. The changes in the quantum mechanical states in the molecules lead to the redistributions in the intensity of the collective magneto-optical response (reflectance) of the arrays made from them. (C) 2009 Elsevier B.V. All rights reserved.
"Negative" diamagnetism of three-dimensional arrays of semiconductor nano-rings
(2013-10-01)
Thu, L. M.
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Chiu, W. T.
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Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We theoretically study the orbital diamagnetic response of three-dimensional arrays of embedded InAs/GaAs wobbled nano-rings. To simulate the rings' magnetic characteristics, we use the effective one band Hamiltonian (energy and position-dependent electron effective mass and Lande factor) and smooth three-dimensional confinement potential that is mapping the actual strain and material content inside the rings. First, we obtain the magnetic susceptibility of an individual nano-ring. Once it is achieved, using the Claussius-Mossotti relation we estimate the effective susceptibility of three-dimensional arrays of the rings. We show that conventionally diamagnetic InAs/GaAs ring structures under certain conditions can demonstrate the positive peak of the effective magnetic susceptibility of the arrays, that we call negative-diamagnetic response. The negative-diamagnetic (positive susceptibility) peak remains Lorentz-like shaped and gradually disappears when the rings' concentration in the arrays decreases. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Optical reflection from a monolayer of embedded nano-objects covered by a thick capping layer
(2008)
Wijers, C. M. J.
;
Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In a hybrid discrete-continuum description the optical response of a capped monolayer of nano-objects has been determined. The monolayer emits a summation of partial plane waves obeying traditional reflection and transmission, enabling solution of the monolayer dipole strength. For thick capping layers the resulting reflection coefficients could be approximated by analytical expressions. These results have been used to investigate the feasibility of experimental detection of the optical response of nano-object monolayers.
Optical response of layers of embedded semiconductor quantum dots
(2006-07-01)
Wijers, C. M. J.
;
Chu, Jiun-Haw
;
Liu, J. L.
;
Voskoboynikov, O.
;
電子工程學系及電子研究所
The influence of the surrounding semiconducting matrix upon the polarizability of embedded nanoobjects (quantum dots) has been investigated. The previously proposed hybrid model has been extended to accommodate the influence of embedding. It turns out that excess discrete dipoles having an excess polarizability against a uniform background identical to the dielectric host material build the basis for a modified discrete dipole model, suited to describe the optical response of this system. The individual dipoles are described by means of dielectric embedded oblate ellipsoids as to their static response. An efficient description of the electrostatics of these ellipsoids has been given in terms of explicit functions using cylindrical coordinates and compatible with similar derivations for spherical dielectric objects. The dynamic contribution, responsible for frequency dependence is determined quantum mechanically and added to the embedded bare polarizability. The result of the model for the particular InAs quantum dot GaAs host combination investigated is a slightly decreased internal reflectance as compared to vacuum and an overall strong increment of the absorbance, the structure in the reflectance and of the ellipsometric angles.
Optical response of quantum dot multilayer structures
(2010)
Thu, L. M.
;
Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We theoretically study optical response of InAs/GaAs quantum dot multilayered structures. Based on the multi-scale hybrid discrete-continuum description the optical response of an isolated layer of embedded quantum dots has been determined. Using the propagation-matrix approach we express the amplitudes of incident, reflected and transmitted electromagnetic waves in a multilayered structure by the reflection and transmission coefficients of the isolated layers. We study the overall reflectance and transmittance dependencies on the number of layers and distance between consecutive layers. The increase of the number of the layers considerably enhances the overall reflectance of the structures. Interference effects become significant for certain distances between layers in the structures.
Optics of embedded semiconductor nano-objects using a hybrid model: bare versus dressed polarizabilities
(2006-11-01)
Wijers, C. M. J.
;
Chu, J. -H.
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Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The influence of the surrounding semiconducting matrix upon the optical response of embedded nano-objects (quantum dots) has been investigated. This system can be described by means of a hybrid model, where the full response is a combination of a macroscopic electrostatic response term and a dynamic response term, obtained quantum mechanically. The result is a modified discrete dipole model, where excess discrete dipoles having an excess polarizability with respect to a uniform background identical to the dielectric host material represent the response. In this model all electrodynamic interactions are screened by the host material. The electrostatic response is obtained by approximating the quantum dots by embedded dielectric oblate ellipsoids. Closed expressions for the electrostatic response of these ellipsoids have been derived. The electrodynamic nature of the dynamic quantum mechanical polarizability term however is unclear. It is not certain whether this polarizability is dressed or bare. Therefore we have investigated in detail the consequences of both options. Although there is no real qualitative difference between them, the difference is so large that experiment can easily discriminate between both. Results should be easily measurable anyhow.
Recent development in simulation and multivariate statistical analysis of physical characteristics of dispersive ensembles of semiconductor nano-sized objects: A brief review
(2014-01-01)
Voskoboynikov, O.
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交大名義發表
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National Chiao Tung University
A general theoretical description of the physical response of dispersive ensembles of semiconductor nano-sized objects of complex geometries, material compositions, and spatial distributions has been developed recently. We present a brief review on some recent results of our simulation of the absorption cross section of dispersive ensembles of ZnTe/CdSe core/shell quantum dots, optical characteristics of ensembles of triple concentric GaAs/AIGaAs nano-rings, and diamagnetic response of ensembles of wobbled InAs/GaAs quantum rings. Simulated by us the actual responses are in a good agreement with experimental data.
Recovery of the Aharonov-Bohm oscillations in asymmetrical quantum rings
(2016-07-01)
Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We theoretically investigate suppression and recovery of the Aharonov-Bohm oscillations of the diamagnetic response of electrons (holes) confined in self-assembled IncGa1-cAs/GaAs semiconductor reflection asymmetrical quantum rings. Based on the mapping method and gauge-origin-independent definition for the magnetic vector potential we simulate the energies and wave functions of the electron (hole) under external magnetic and electric fields. We examine the transformation of the ground state wave function of the electron (hole) in reflection asymmetrical rings from localized in one of the potential valleys (dotlike shape of the wave function) to distributed over all volume of the ring (ringlike shape) under an appropriate lateral electric field. This transformation greatly recovers the electron (hole) diamagnetic coefficient and Aharonov-Bohm oscillations of the diamagnetic response of the ring. However, the recovering electric field for the first Aharonov-Bohm diamagnetic oscillation of the electron is a suppressing one for the hole (and vice versa). This can block the recovery of the optical Aharonow-Bohm effect in IncGa1-cAs/GaAs asymmetrically wobbled rings. However, the recovery of the Aharonov-Bohm oscillations for the independent electron (hole) by the external electric field remains interesting and feasible objective for the asymmetric rings. (C) 2016 Author(s).
Simulation of an Asymmetrical Nano Ring by Mapping of the Realistic Electronic Confinement Potential
(2010)
Thu, L. M.
;
Voskoboynikov, O.
;
交大名義發表
;
National Chiao Tung University
In this paper we propose a computational method which uses smooth three dimensional confinement potentials for description of the electronic properties of semiconductor nano objects. The potential is mapping the actual (known from experiment) geometrical, structural, and material composition of the objects. Using the mapping we are able to formulate an effective electronic Hamiltonian and in a very efficient manner obtain the energy states and wave functions of the electrons confined in the object. We demonstrate the approach efficiency considering influence of In distribution in an asymmetrical InAs/GaAs nano ring on the magnetic response of the object.
Temperature stable positive magnetic susceptibility of semiconductor wobbled nano rings
(2010)
Thu, L. M.
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Chiu, W. T.
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Voskoboynikov, O.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We theoretically investigate the magnetic response of ensembles of semiconductor nano rings. Using our mapping method we simulated geometrical and material dispersion of the magnetic susceptibility of ensembles of the rings. Unlike the susceptibility of an individual ring the averaged susceptibility shows small temperature effect.