Browsing by Author "Thu, L. M."

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Binding energy of magneto-biexcitons in semiconductor nano-rings
(2010)
Thu, L. M.
;
Chiu, W. T.
;
Xue, Shao-Fu
;
Lin, Ta-Chun
;
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.
;
Chiu, W. T.
;
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.
;
Voskoboynikov, O.
;
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.
;
Chiu, W. T.
;
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.
Exciton wave function localization and exciton diamagnetic coefficient in semiconductor quantum rings without reflection symmetry
(2013-08-12)
Voskoboynikov, Oleksandr
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Chiu, W. T.
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Thu, L. M.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We theoretically study how reflection asymmetry affects the neutral exciton diamagnetic coefficient in self-assembled InGaAs/GaAs semiconductor wobbled quantum rings. The previously proposed mapping method is used to simulate the exciton wave function and energy in the rings. The description is suited to clarify the important question of the exciton diamagnetic coefficient stability in the rings with broken reflection symmetry. Our simulation results confirm that the exciton wave function of the reflection symmetrical (balanced) wobbled ring is distributed equally over two potential valleys corresponding to the hills in the ring's shape. At the same time, even a very small reflectional imbalance in the geometry and (or) material content of the wobbled rings destroys the ringlike shape of the exciton wave function and causes the localization of the function in one of the potential valleys of the ring (dotlike shape of the exciton wave function). This leads to a rapid decrease of the exciton diamagnetic coefficient. Our calculation results are in good agreement with recent experimental observations.
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.
;
Chiu, W. T.
;
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 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.
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.
;
Chiu, W. T.
;
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.
Unusual Diamagnetism in Semiconductor Nano-Objects
(2010)
Thu, L. M.
;
Voskoboynikov, O.
;
交大名義發表
;
National Chiao Tung University
We theoretically consider the diamagnetic response of an InAs/GaAs asymmetrical nano-ring and asymmetrical quantum dot molecule when external magnetic field is applied in the system's growth directions. We use the effective one-electronic-band Hamiltonian (energy-position-dependent electron effective mass and g-factor approximation) with smooth full three-dimensional confinement potentials mapping actual strain and material content in those nano-objects. This approach allows us to simulate and study physical properties of semiconductor nano-objects within a wide range of change in geometry and parameters. Although the geometries of the systems investigated are very different, we found for both systems a similar magnetic response. At low temperature the single electron differential magnetic susceptibility has a positive peak and with temperature increasing the peak remain Lorenzt-like shaped and gradually disappear.