Browsing by Author "Hsiao, R. S."

Now showing 1 - 7 of 7

Evidence for the electron trap state associated with N-rich clusters in InGaAsN/GaAs quantum wells
(2007-06-13)
Chen, J. F.
;
Hsieh, P. C.
;
Hsiao, R. S.
;
Wang, J. S.
;
Chi, J. Y.
An electron trap state has been found to appear in InGaAsN/GaAs quantum wells ( QWs) as a result of composition fluctuation. Evidence of composition fluctuation is shown by photoluminescence spectra which display an additional low-energy emission due to local regions of N-rich clusters. Enhancing composition fluctuation leads to undulated InGaAsN/GaAs interface with dot-like islands. The capacitance-voltage profiling shows an additional peak following the QW electron ground state peak, suggesting the presence of an electron trap state below the QW electron ground state. The emission properties of this trap state are similar to those of quantum dots immersed in a well. Enhancing composition fluctuation can cause an energy downward shift and spectral broadening of this electron trap state, suggesting an increase in island size and fluctuations of the size and composition. Thus, it is deduced that the electron trap state originated from the N-rich clusters in the well behaving like quantum dots. Upon modulation, the electrons are thermally activated from this trap state to the QW electron ground state and subsequently emitted to the GaAs bottom electrode.
Photoluminescence studies of InAs/GaAs quantum dots covered by InGaAs layers
(2010-01-15)
Shu, G. W.
;
Wang, J. S.
;
Shen, J. L.
;
Hsiao, R. S.
;
Chen, J. F.
Photoluminescence (PL), PL excitation (PLE), and time-resolved PL were used to study effects of InGaAs layers on the optical properties of InAs/GaAs quantum dots (QDs). A rich fine structure in the excited states of confined excitons (up to n = 4 quantum states) was observed, providing useful information to study the quantum states in the InAs/GaAs QDs. A significant redshift of the PL peak energy for the QDs covered by InGaAs layers was observed, attributing to the decrease of the QD strain and the lowing of the quantum confinement. (C) 2009 Elsevier B.V. All rights reserved.
Relaxation-induced lattice misfits and their effects on the emission properties of InAs quantum dots
(2007-09-05)
Chen, J. F.
;
Wang, Y. Z.
;
Chiang, C. H.
;
Hsiao, R. S.
;
Wu, Y. H.
Strain relaxation in InAs/InGaAs quantum dots (QDs) is shown to introduce misfits in the QD and neighboring GaAs bottom layer. A capacitance -voltage profiling shows an electron accumulation peak at the QD with a long emission time, followed by additional carrier depletion caused by the misfits in the GaAs bottom layer. The emission-time increase is explained by the suppression of tunneling for the QD excited states due to the additional carrier depletion. As a result, electrons are thermally activated from the QD states to the GaAs conduction band, consistent with observed emission energies of 0.160 and 0.068 eV which are comparable to the confinement energies of the QD electron ground and first-excited states, respectively, relative to the GaAs conduction band. This is in contrast to non-relaxed samples in which emission energy of 60 meV is observed, corresponding to the emission from the QD ground state to the first-excited state.
Single-mode InGaAs submonolayer quantum dot photonic crystal VCSELs
(2006-08-01)
Yang, H. P. D.
;
Hsu, I. C.
;
Lai, F. I.
;
Lin, G.
;
Hsiao, R. S.
An InGaAs submonolayer ( SML) quantum dot photonic crystal vertical-cavity surface-emitting laser ( QD PhC-VCSEL) for fibre-optic applications is demonstrated for the first time. The active region of the device contains three InGaAs SML QD layers. Each of the InGaAs SML QD layers is formed by alternate deposition of InAs (< 1 ML) and GaAs. Single-fundamental-mode CW output power of 3.8 mW at 28 mA has been achieved in the 990 nm range, with a threshold current of 0.9 mA. A side-mode suppression ratio ( SMSR) larger than 35 dB has been observed over the entire current operating range.
Strain relaxation and induced defects in InAsSb self-assembled quantum dots
(2006-06-05)
Chen, J. F.
;
Hsiao, R. S.
;
Huang, W. D.
;
Wu, Y. H.
;
Chang, L.
The onset of strain relaxation and induced defects in InAs0.94Sb0.06 quantum dots are investigated. We show that the relaxation causes partial carrier depletion in the dots and drastic carrier depletion in the top GaAs layer due to the introduction of two defect traps At 0.35 and 0.64 eV. This result is consistent with transmission electron microscopy data which show misfit dislocations on the edges of the dot upper boundary and threading dislocations in the top GaAs layer. The bottom GaAs layer is dislocation-free, and thus the strain relaxation may initially occur on the edges of the dots. (c) 2006 American Institute of Physics.
The photoluminescence decay time of self-assembled InAs quantum dots covered by InGaAs layers
(2006-12-14)
Shu, G. W.
;
Wang, C. K.
;
Wang, J. S.
;
Shen, J. L.
;
Hsiao, R. S.
The temperature dependence of the time-resolved photoluminescence (PL) of self-assembled InAs quantum dots (QDs) with InGaAs covering layers was investigated. The PL decay time increases with temperature from 50 to 170 K, and then decreases as the temperature increases further above 170 K. A model based on the phonon-assisted transition between the QD ground state and the continuum state is used to explain the temperature dependence of the PL decay time. This result suggests that the continuum states are important in the carrier capture in self-assembled InAs QDs.
Wire-like characteristics in stacked InAs/GaAs quantum dot superlattices for optoelectronic devices
(2007-09-01)
Chen, T. T.
;
Chen, Y. F.
;
Wang, J. S.
;
Huang, Y. S.
;
Hsiao, R. S.
The wire-like characteristics of stacked InAs/GaAs quantum dot (QDs) superlattices induced by the vertically electronic coupling effect were demonstrated by surface photovoltaic and photoluminescence measurements. It was found that the surface photovoltaic signal can be enhanced by up to more than 100 times due to the wire-like behavior along the growth direction. We also found that the emission from the cleaved edge surface is strongly anisotropic, which suggests a possibility of fine tuning the polarization by changing the spacer thickness. Additionally, the electroluminescence of stacked QDs near 1.3 mu m based on the wire-like characteristics has a much better performance than that of uncoupled QDs.