Browsing by Author "Fu, Ying-Jhe"

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Design and demonstration of high quality-factor H1-cavity in two-dimensional photonic crystal
(2013-11-15)
Fu, Ying-Jhe
;
Lee, Yi-Shan
;
Lin, Sheng-Di
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We introduce a method for designing an H1 photonic crystal cavity to enhance its quality factor (Q factor). The highest theoretical Q factor of 120,000 is obtained. The Fourier transformation of field distribution shows that the enhancement arises from the component reduction of a leaky mode. The Q-factor improvement has also been demonstrated experimentally with the highest value of 11,700. Our design could be useful for studying light-matter interaction in an H1 cavity as the mode volume only increases slightly. (C) 2013 Optical Society of America
Imbalanced initial populations between dark and bright states in semiconductor quantum dots
(2012-08-27)
Lin, Sheng-Di
;
Fu, Ying-Jhe
;
Cheng, Chun
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We present the observation and analysis of long-lived exciton in individual InAs quantum dots (QDs). The general model considering the interplay between dark and bright states reveals the two key factors responsible for the long decay time: the shortened spin-flip time at elevated temperature and the imbalanced initial populations between the dark and bright states. The later one plays a key role in the unusual phenomena and leads to the possibility of spin-dependent relaxation process in QDs. (C) 2012 Optical Society of America
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
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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.
Observation of long-lived excitons in InAs quantum dots under thermal redistribution temperature
(2012-03-26)
Cheng, Chun
;
Lin, Sheng-Di
;
Pan, Chien-Hung
;
Lin, Chien-Hung
;
Fu, Ying-Jhe
We study the temperature-dependent time-resolved photoluminescence (TRPL) of self-assembled InAs quantum dots (QDs). Under low excitation power, a surprisingly long PL decay time is observed at about 60 K, under the thermal redistribution temperature. The long decay time decreases with increasing excitation power but is nearly independent of the detection energy of TRPL measurements. A model considering the spin relaxation through the excited excitonic state is proposed to quantitatively explain the unusual phenomena. The rate equation analysis indicates that the observation of long-lived excitons is caused by the shortened spin-flip time. (c) 2012 Elsevier B.V. All rights reserved.
Selecting detection wavelength of resonant cavity-enhanced photodetectors by guided-mode resonance reflectors
(2012-02-13)
Lai, Kuo-Wei
;
Lee, Yi-Shan
;
Fu, Ying-Jhe
;
Lin, Sheng-Di
;
電子工程學系及電子研究所
We propose and demonstrate a novel device structure of resonant cavity-enhanced photodetector (RCE-PD). The new RCE-PD structure consists of a bottom distributed Bragg reflector (DBR), a cavity with InGaAs multiple quantum wells (MQWs) for light absorption and a top mirror of sub-wavelength grating. By changing the fill factor of the 2-D grating, the effective cavity length of RCE-PDs can be varied so the resonant wavelength can be selected post growth. Accordingly, we can fabricate an array of PDs on a single chip, on which every PD aims for a specific wavelength. (C) 2012 Optical Society of America