Browsing by Author "Lin, Hsuan"

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Diamagnetic Response of Exciton Complexes in Semiconductor Quantum Dots
(2008-12-31)
Tsai, Ming-Fu
;
Lin, Hsuan
;
Lin, Chia-Hsien
;
Lin, Sheng-Di
;
Wang, Sheng-Yun
We report measurements of diamagnetic shifts for different exciton complexes confined in small InAs quantum dots. The measured diamagnetic responses are sensitive to the number of carriers in the exciton complexes, with systematic differences between neutral excitons, biexcitons, and trions. Theoretical calculations suggest that such systematic differences arise from very different extents of electron and hole wave functions confined in small quantum dots. The measured magnetic response of Coulomb energies is found to vary with the cube of the wave function extent, and can be a sensitive probe to the electron-hole wave function asymmetry.
Effects of growth temperature on InN/GaN nanodots grown by metal organic chemical vapor deposition
(2008-05-15)
Chang, Wen-Hao
;
Ke, Wen-Cheng
;
Yu, Shu-Hung
;
Lee, Lin
;
Chen, Ching-Yu
InN nanodots grown on GaN by metal organic chemical vapor deposition using conventional growth mode as well as flow-rate modulation epitaxy at various growth temperatures (550-730 degrees C) were investigated. We found that different precursor injection schemes together with the effect of growth temperatures greatly influenced the surface morphology of InN nanodots and their photoluminescence (PL) properties. The sample grown at around 650 degrees C showed the highest growth rate. For samples grown at higher temperatures, the residual carrier concentration was reduced and the PL efficiency was improved. Furthermore, we found that the growth of InN nanodots is still sustainable even at a temperature higher than 700 degrees C while retaining their optical quality. (c) 2008 American Institute of Physics.
Exciton fine structures and energy transfer in single InGaAs quantum-dot molecules
(2009)
Lin, Hsuan
;
Wang, Sheng-Yun
;
Lin, Chia-Hsien
;
Chang, Wen-Hao
;
Cheng, Shun-Jen
We present a spectroscopic study of single quantum-dot molecules (QDMs) formed by two closely stacked In(0.5)Ga(0.5)As/GaAs layers. It was found that the interdot coupling and directional energy transfer between the two adjacent dots can be controlled by temperature tuning. Direct and indirect excitons, as well as charged excitons in single QDMs were classified and identified by excitation-power dependent, excitation-energy dependent and polarization-resolved microphotoluminescence measurements. With the increasing temperature, the direct-exciton intensity decreases while the indirect-exciton intensity increases. A rate equation model considering phonon mediated processes has been developed. The directional energy transfer in QDMs is explained in terms of the phonon-assisted tunnelling of hole between the two adjacent dots. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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.
Nonresonant carrier transfer in single InGaAs/GaAs quantum dot molecules
(2008-06-01)
Chang, Wen-Hao
;
Lin, Hsuan
;
Wang, Sheng-Yun
;
Lin, Chia-Hsien
;
Cheng, Shun-Jen
We present a spectroscopic study of single quantum dot molecules (QDMs) formed by two closely stacked In(0.5)Ga(0.5)As layers. The exciton fine structures as well as direct and indirect excitonic species associated with QDMs were identified by power dependent and polarization resolved microphotoluminescence measurements. As the temperature was increased, a directional energy transfer between the direct and indirect excitons in single QDMs was observed. A rate-equation model was developed to explain our data. We show that a phonon-assisted nonresonant tunneling of the hole between the two adjacent dots is responsible for such directional energy transfers in QDMs.
Stress tuning of strong and weak couplings between quantum dots and cavity modes in microdisk microcavities
(2011-11-01)
Lin, Hsuan
;
Lin, Chia-Hsien
;
Lai, Wei-Chen
;
Lee, Yi-Shan
;
Lin, Sheng-Di
We present the control of couplings between quantum dots and cavity modes in microdisk microcavities by a stress tuning scheme. The excitonic transitions and cavity modes can be brought into resonance due to their different energy shift rates with the applied strain. Spectral signatures of both strong and weak couplings are clearly observed. The strain tunable device can be used to tune the exciton wavelength bidirectionally at constant temperatures without significantly affecting the emission rate and linewidth of excitons.
Strong coupling of different cavity modes in photonic molecules formed by two adjacent microdisk microcavities
(2010-11-08)
Lin, Hsuan
;
Chen, Jhih-Hao
;
Chao, Shih-Shing
;
Lo, Ming-Cheng
;
Lin, Sheng-Di
Strong couplings between cavity modes in photonic molecules formed by two preselected nearly identical microdisk microcavities with embedded quantum dots are investigated. By continuously tuning the refractive index of one microdisk, clear anticrossings in the resonant peak energies associated with crossings in the peak linewidths can be observed. The coupling strengths are extracted by the coupled mode theory and analyzed by the model considering the effective potential confining the electromagnetic waves in the microcavities. (C) 2010 Optical Society of America
Strong coupling of different cavity modes in photonic molecules formed by two adjacent microdisk microcavities
(2010-11-08)
Lin, Hsuan
;
Chen, Jhih-Hao
;
Chao, Shih-Shing
;
Lo, Ming-Cheng
;
Lin, Sheng-Di
Strong couplings between cavity modes in photonic molecules formed by two preselected nearly identical microdisk microcavities with embedded quantum dots are investigated. By continuously tuning the refractive index of one microdisk, clear anticrossings in the resonant peak energies associated with crossings in the peak linewidths can be observed. The coupling strengths are extracted by the coupled mode theory and analyzed by the model considering the effective potential confining the electromagnetic waves in the microcavities. (C) 2010 Optical Society of America
Structural and optical properties of In-rich InGaN nanodots grown by metallo-organic chemical vapor deposition
(2007-10-10)
Tsai, Wen-Che
;
Lin, Hsuan
;
Ke, Wen-Chen
;
Chang, Wen-Hao
;
Chou, Wu-Ching
The surface morphologies, alloy compositions and emission properties of In- rich InxGa1-xN nanodots ( x >= 0.87) grown by metallo-organic chemical vapor deposition at various growth temperatures (550-750 degrees C) were investigated. We found that the nucleation of InGaN dots was dominated by the surface migration of In adatoms. A higher Ga content can be achieved at lower growth temperatures due to the relatively lower migration ability of Ga adatoms. At higher growth temperatures, the InGaN dots tend to decompose into In- rich islands and a thin Ga-rich layer. These In- rich islands exhibit photoluminescence emission in the near-infrared range. Another visible emission band was also observed for samples grown at higher temperatures. The formation of a thin Ga-rich layer is likely to be responsible for the visible emission.
Structural and optical properties of indium-rich InGaN islands
(2008)
Tsai, Wen-Che
;
Lin, Hsuan
;
Ke, Wen-Chen
;
Chang, Wen-Hao
;
Chou, Wu-Ching
Indium-rich InxGa1-xN islands (x >= 0.87) grown by metalor-ganic chemical vapor deposition at growth temperatures ranging from 550-750 degrees C were investigated. With the increasing growth temperature, the InGaN dot size increases while the dot density decreases due to the enhanced surface migration of In/Ga adatoms at elevated temperatures. In addition, the compositiom of InGaN-islands was also found to be varied with the growth temperature. At lower growth temperatures, a higher Ga content can be achieved due to the relatively lower migration ability of Ga adatoms. At higher growth temperatures, the deposited InGaN material tend to decompose into In-rich islands and a thin Ga-rich layer, Photoluminescence investigations show that these In-rich islands exhibit a near-infrared emission band . For samples grown at higher temperatures a visible emission band was also observed. The visible emission band may arise from defect hands introduced during the formation of Ga-rich InGaN layer. (c) 2008 WILEY-VCH Veriag GmbH & Co. KGaA, Weinheim.
Structural and optical properties of InN/GaN nanodots grown by metalorganic chemical vapor deposition
(2008)
Chang, Wen-Hao
;
Lee, Lin
;
Chen, Ching-Yu
;
Tsai, Wen-Che
;
Lin, Hsuan
InN nanodots grown on GaN by metalorganic chemical vapor deposition (MOCVD) using conventional growth mode as well as flow-rate modulation epitaxy (FME) at various growth temperatures (550-730 degrees C) were investigated. We found that different precursor injection schemes together with the effect of growth temperatures greatly influenced the surface morphology of InN dots and their photoluminescence (PL) properties. The best growth efficiency of InN was achieved by FME at around 650 degrees C. The residual carrier concentration and PL efficiency was also be improved when a high growth temperature was used. Our results indicated that InN nanodots can be grown at a temperature even higher than 700 degrees C while maintain their optical quality. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.