Browsing by Author "Chiu, W. T."

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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.
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.
Exciton wave function localization and exciton diamagnetic coefficient in semiconductor quantum rings without reflection symmetry
(2013-08-12)
Voskoboynikov, Oleksandr
;
Chiu, W. T.
;
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.
"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
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.