Browsing by Author "Lin, Ta-Chun"

Now showing 1 - 6 of 6

Anomalous optical magnetic shift of self-assembled GaSb/GaAs quantum dots
(2011-07-01)
Lin, Ta-Chun
;
Li, Liang-Chen
;
Lin, Sheng-Di
;
Suen, Yuen-Wuu
;
Lee, Chien-Ping
We report the magneto-photoluminescence (PL) measurement results on type-II self-assembled GaSb/GaAs quantum dots with the magnetic field applied in Faraday and Voigt configurations. The emission of the quantum dots exhibited a typical diamagnetic blueshift when the magnetic field was applied in a Faraday configuration. However, when the magnetic field was in the Voigt configuration, an unusual redshift in the emission peak accompanied with a rapid increase of the PL intensity was observed. Guided by numerical calculations, the magnetic field applied in the Voigt configuration is found to provide an additional vertical confinement to electrons, and therefore, substantially enhance the radiative electron-hole recombination. The resulting decrease of the steady-state hole concentration gives rise to the observed anomalous magnetic redshift. (C) 2011 American Institute of Physics. [doi:10.1063/1.3607973]
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
Effects of crossed states on photoluminescence excitation spectroscopy of InAs quantum dots
(2011-06-02)
Shih, Ching-I
;
Lin, Chien-Hung
;
Lin, Shin-Chin
;
Lin, Ta-Chun
;
Sun, Kien Wen
In this report, the influence of the intrinsic transitions between bound-to-delocalized states (crossed states or quasicontinuous density of electron-hole states) on photoluminescence excitation (PLE) spectra of InAs quantum dots (QDs) was investigated. The InAs QDs were different in size, shape, and number of bound states. Results from the PLE spectroscopy at low temperature and under a high magnetic field (up to 14 T) were compared. Our findings show that the profile of the PLE resonances associated with the bound transitions disintegrated and broadened. This was attributed to the coupling of the localized QD excited states to the crossed states and scattering of longitudinal acoustical (LA) phonons. The degree of spectral linewidth broadening was larger for the excited state in smaller QDs because of the higher crossed joint density of states and scattering rate.
Impacts of Coulomb Interactions on the Magnetic Responses of Excitonic Complexes in Single Semiconductor Nanostructures
(2010-04-01)
Chang, Wen-Hao
;
Lin, Chia-Hsien
;
Fu, Ying-Jhe
;
Lin, Ta-Chun
;
Lin, Hsuan
We report on the diamagnetic responses of different exciton complexes in single InAs/GaAs self-assembled quantum dots (QDs) and quantum rings (QRs). For QDs, the imbalanced magnetic responses of inter-particle Coulomb interactions play a crucial role in the diamagnetic shifts of excitons (X), biexcitons (XX), and positive trions (X (-) ). For negative trions (X (-) ) in QDs, anomalous magnetic responses are observed, which cannot be described by the conventional quadratic energy shift with the magnetic field. The anomalous behavior is attributed to the apparent change in the electron wave function extent after photon emission due to the strong Coulomb attraction by the hole in its initial state. In QRs, the diamagnetic responses of X and XX also show different behaviors. Unlike QDs, the diamagnetic shift of XX in QRs is considerably larger than that of X. The inherent structural asymmetry combined with the inter-particle Coulomb interactions makes the wave function distribution of XX very different from that of X in QRs. Our results suggest that the phase coherence of XX in QRs may survive from the wave function localization due to the structural asymmetry or imperfections.
Impacts of structural asymmetry on the magnetic response of excitons and biexcitons in single self-assembled In(Ga)As quantum rings
(2009-08-01)
Lin, Ta-Chun
;
Lin, Chia-Hsien
;
Ling, Hong-Shi
;
Fu, Ying-Jhe
;
Chang, Wen-Hao
The diamagnetic shifts of neutral excitons and biexcitons confined in single self-assembled In(Ga)As/GaAs quantum rings are investigated. Unlike quantum dots, quantum rings reveal a considerably large biexciton diamagnetic shift, about two times larger than that of single excitons. Based on model calculations, we found that the inherent structural asymmetry and imperfection, combined with the interparticle Coulomb interactions, is the fundamental cause of the more extended biexciton wave function in the quantum rings. The exciton wave function tends to be localized in one of the potential valleys induced by structural imperfections of the quantum ring due to the strong localization of hole and the electron-hole Coulomb attraction, resembling the behavior in single dots. Our results suggest that the phase coherence of neutral excitons in quantum rings will be smeared out by such wave function localizations.