Browsing by Author "Chi, J. Y."

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Anisotropy light extraction with high polarization ratio from photonic crystal fight-emitting diodes
(2008)
Lai, Chun-Feng
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Kuo, Hao-Chung
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Lu, Tien-Chang
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Wang, Shing-Chang
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Chao, C. H.
The azimuthal anisotropy of GaN photonic crystal light-emitting diode is investigated using an annular structure. The extracted light distribution has P/S ratio of 5.5 for fight propagating in Gamma X direction and 2.1 for Gamma M direction. @2007 Optical Society of America
Anisotropy of light extraction from two-dimensional photonic crystal light-emitting diodes
(2007-09-17)
Lai, Chun-Feng
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Kuo, H. C.
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Chao, C. H.
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Hsueh, H. T.
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Wang, J.-F. T.
Anisotropic light extraction of photonic crystal (PhC) light-emitting diodes in the azimuthal direction has been investigated with an annular structure of triangular PhC lattice. The optical images of the photoluminescence light extraction are obtained with laser excitation. For increasing lattice constant, sixfold symmetric patterns with varying numbers of petals in multiples of six are observed and analyzed. A map of the anisotropy for various lattice constants and numerical apertures is constructed. Several features of light propagations associated with the PhC are observed including the focusing and collimating behaviors.(c) 2007 American Institute of Physics.
Azimuthal anisotropy of light extraction from photonic crystal light-emitting diodes
(2008)
Lai, Chun-Feng
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Kuo, H. C.
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Chao, C. H.
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Hsueh, H. T.
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Wang, J. -F. T.
Photonic crystal (PhC) light-emitting diodes (LEDs) exhibiting anisotropic light extraction have been investigated experimentally and theoretically. It is found that the anisotropic light extraction strongly depends on the lattice constant and orientation. Optical images of the anisotropy in the azimuthal direction are obtained using annular structure with triangular lattice. 6-fold symmetric light extraction patterns with varying number of petals are observed. More petals in multiple of 6 appear in the observed image with lattice constant increasing. This anisotropic behavior suggests a new means to optimize the PhC design of GaN LED for light extraction.
Azimuthal anisotropy of light extraction from photonic crystal light-emitting diodes
(2007)
Hsuch, H. T.
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Wang, J. -F. T.
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Chao, C. H.
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Yeh, W. Y.
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Chi, J. Y.
Photonic crystal light-emitting diodes exhibiting anisotropic light extraction efficiency have been investigated experimentally and theoretically. Images of the anisotropy in the azimuthal direction are obtained using annular structures with triangular lattice. Depending on the lattice constants, 6-fold symmetric patterns with varying number of petals are obtained.
Demonstration of slow light via population oscillation in quantum dot VCSEL
(2007)
Xuan, R.
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Chi, J. Y.
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Peng, P. C.
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Yang, H. P.
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Chao, C. L.
Experimental data for slow light delay in a quantum dot VCSEL are analyzed with a Fabry-Perot analysis. The analysis can fit the observed wavelength dependence of the delay. It can also explain that the maximum delay occur at a wavelength detuned from the resonant frequency.
Effect of antimony incorporation on the density, shape, and luminescence of InAs quantum dots
(2008-07-15)
Chen, J. F.
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Chiang, C. H.
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Wu, Y. H.
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Chang, L.
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Chi, J. Y.
This work investigates the surfactant effect on exposed and buried InAs quantum dots (QDs) by incorporating Sb into the QD layers with various Sb beam equivalent pressures (BEPs). Secondary ion mass spectroscopy shows the presence of Sb in the exposed and buried QD layers with the Sb intensity in the exposed layer substantially exceeding that in the buried layer. Incorporating Sb can reduce the density of the exposed QDs by more than two orders of magnitude. However, a high Sb BEP yields a surface morphology with a regular periodic structure of ellipsoid terraces. A good room-temperature photoluminescence (PL) at similar to 1600 nm from the exposed QDs is observed, suggesting that the Sb incorporation probably improves the emission efficiency by reducing the surface recombination velocity at the surface of the exposed QDs. Increasing Sb BEP causes a blueshift of the emission from the exposed QDs due to a reduction in the dot height as suggested by atomic force microscopy. Increasing Sb BEP can also blueshift the similar to 1300 nm emission from the buried QDs by decreasing the dot height. However, a high Sb BEP yields a quantum well-like PL feature formed by the clustering of the buried QDs into an undulated planar layer. These results indicate a marked Sb surfactant effect that can be used to control the density, shape, and luminescence of the exposed and buried QDs. (C) 2008 American Institute of Physics.
Evidence for the electron trap state associated with N-rich clusters in InGaAsN/GaAs quantum wells
(2007-06-13)
Chen, J. F.
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Hsieh, P. C.
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Hsiao, R. S.
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Wang, J. S.
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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.
Modeling of slow light in vertical cavity surface emission lasers
(2007)
Chou, C. -S.
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Lee, R. -K.
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Peng, P. C.
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Kuo, H. C.
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Lin, G.
We develop a model for the slow light in the Vertical Cavity Surface Emission Lasers (VCSELs), with the combinations of cavity and the population pulsation effects. The dependences of pumping power, injection current and wavelength detuning for the group delays are demonstrated theoretically and experimentally. Up to 65 ps group delays and up to 10 GHz modulation frequency can be achieved in the room temperature at the wavelength of 1.3 mu m. Based on the experimental parameters of quantum dot VCSEL structures, we show that the resonance effect of laser cavity plays a significant role to enhance the group delays.
Novel chirped multilayer quantum-dot lasers
(2008-01-01)
Lin, G.
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Chang, C. Y.
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Tseng, W. C.
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Lee, C. P.
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Lin, K. F.
Chirped multilayer (N=10) QD lasers with 2-, 3- and 5-layer of longer-, medium-, and shorter-wavelength QD stacks, respectively, were grown in this work. Low threshold current density and high saturated modal gain were achieved in this specially designed QD structure. Empirical gain-current analysis was performed on this chirped multilayer QD structure for the first time. It was consistent with our spectral observations and provided valuable information on carrier recombination in chirped multilayer QD structure. Two novel spectral characteristics were discovered also for the first time. First, simultaneous two-wavelength lasing around threshold was observed under particular gain-loss condition at this specific multilayer structure of QD stacking numbers. Second, at cryogenic temperature, simultaneous two-wavelength lasing emissions switched from longer-wavelength lasing first to shorter-wavelength lasing first with increasing current injection. Non-uniform carrier distribution among chirped multilayer QD structure is evident at low temperature below 200 K from our analysis.
Novel chirped multilayer quantum-dot lasers - art. no. 69970R
(2008)
Lin, G.
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Chang, C. Y.
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Tseng, W. C.
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Lee, C. P.
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Lin, K. F.
Chirped multilayer (N=10) QD lasers with 2-, 3- and 5-layer of longer-, medium-, and shorter-wavelength QD stacks, respectively, were grown in this work. Low threshold current density and high saturated modal gain were achieved in this specially designed QD structure. Empirical gain-current analysis was performed on this chirped multilayer QD structure for the first time. It was consistent with our spectral observations and provided valuable information on carrier recombination in chirped multilayer QD structure. Two novel spectral characteristics were discovered also for the first time. First, simultaneous two-wavelength lasing around threshold was observed under particular gain-loss condition at this specific multilayer structure of QD stacking numbers. Second, at cryogenic temperature, simultaneous two-wavelength lasing emissions switched from longer-wavelength lasing first to shorter-wavelength lasing first with increasing current injection. Non-uniform carrier distribution among chirped multilayer QD structure is evident at low temperature below 200 K from our analysis.
Optical property improvement of InAs/GaAs quantum dots grown by hydrogen-plasma-assisted molecular beam epitaxy
(2011-05-01)
Katkov, A. V.
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Wang, C. C.
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Chi, J. Y.
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Cheng, C.
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Gutakovskii, A. K.
An order-of-magnitude increase of photoluminescence (PL) efficiency at room temperature has been observed in the GaAs/InAs quantum dots (QDs)-in-a-well structure grown with in situ irradiation of atomic hydrogen supplied by a radio-frequency hydrogen-plasma source. The enhancement in PL intensity rapidly increases with the hydrogen flow rate and is stable with a variation of excitation power in the radio-frequency plasma source. Extensive thermal annealing of grown samples up to 634 degrees C did not show any significant degradation of photoluminescence intensity compared with the reference sample. The reduction of nonradiative recombination centers in the as-grown sample causes the greatly enhanced luminescence property. In addition to PL enhancement the authors observed that the H-assisted growth of InAs QDs has suppressed bimodal distribution of QD shape. In contrast to the hydrogen-plasma-assisted growth, irradiation by hydrogen in molecular form has a detrimental effect on the optical properties of similar structures. The high thermal stability of improved optical properties suggests that the formation of the defects which are responsible for nonradiative recombination channels is suppressed during H-assisted epitaxy although in situ defect passivation by atomic hydrogen cannot be completely ruled out. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3570870]
Polarization Switching in 1.3-mu m Quantum Dot Vertical Cavity Surface Emitting Lasers
(2009)
Wu, F. M.
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Lan, R. L.
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Peng, P. C.
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Huang, C. C.
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Peng, R. Y.
This work for the first time, experimentally demonstrates the polarization switching in 1.3 mu m quantum dot VCSEL. The polarization switching in quantum dot VCSEL is achieved by adjusting the optical injection power. (C)2009 Optical Society of America
Relaxation-induced lattice misfits and their effects on the emission properties of InAs quantum dots
(2007-09-05)
Chen, J. F.
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Wang, Y. Z.
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Chiang, C. H.
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Hsiao, R. S.
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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.
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Hsu, I. C.
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Lai, F. I.
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Lin, G.
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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.
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Hsiao, R. S.
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Huang, W. D.
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Wu, Y. H.
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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.
Strain relaxation in InAs self-assembled quantum dots induced by a high N incorporation
(2008-11-15)
Chen, J. F.
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Yang, C. H.
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Wu, Y. H.
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Chang, L.
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Chi, J. Y.
The effect of a high N incorporation in self-assembled InAs quantum dots (QDs) is investigated by analyzing the electronic and structural properties around QD region. Capacitance-voltage profiling and admittance spectroscopy shows that N incorporation into the InAs QD layer leads to drastic carrier depletion in the QD layer and neighboring GaAs layers due to the formation of a deep defect state at 0.34-0.41 eV. The signature of this defect state is similar to those defects observed in strain relaxed QDs or InGaAs/GaAs quantum wells when the InAs deposition thickness exceeds a critical thickness. Accordingly, the N incorporation might result in strain relaxation either by increasing localized strain or by inducing composition inhomogeneities, which provide nucleation sources for strain relaxation. The argument of strain relaxation is supported by transmission electron microscopy that reveals lattice misfits at the QD layer and neighboring GaAs layers.
Tunable optical group delay in quantum dot vertical-cavity surface-emitting laser at 10 GHz
(2006-08-31)
Peng, P. C.
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Lin, C. T.
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Kuo, H. C.
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Lin, G.
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Tsai, W. K.
This investigation experimentally demonstrates tunable optical group delay in a 1.3 mu m quantum dot vertical-cavity surface-emitting laser (QD VCSEL). The QD VCSEL is fabricated on a GaAs substrate. Tunable delays are achieved by varying the bias currents, and the maximum delay of 42 ps at 10 GHz has been demonstrated at room temperature.
Tunable slow light device using quantum dot semiconductor laser
(2006-12-25)
Peng, P. C.
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Lin, C. T.
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Kuo, H. C.
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Tsai, W. K.
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Liu, J. N.
This investigation experimentally demonstrates a tunable slow light device using a quantum dot (QD) semiconductor laser. The QD semiconductor laser at 1.3 mu m fabricated on a GaAs substrate is grown by molecular beam epitaxy. Tunable slow light can be achieved by adjusting the bias current and wavelength detuning. The slow light device operated under probe signal from 5 to 10 GHz is presented. Moreover, we also demonstrate that the tunable slow light device can be used in a subcarrier multiplexed system. (C) 2006 Optical Society of America.
Wavelength switching based on quantum-dot vertical-cavity surface-emitting laser
(2012-09-01)
Peng, P. C.
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Wang, H. Y.
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Lan, R. L.
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Lu, H. H.
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Lin, G. R.
This study investigates, for the first time, static and dynamic wavelength switching characteristics of the 1.3 mu m quantum-dot vertical-cavity surface-emitting laser (QD VCSEL). The free-running QD VCSEL with lambda 1 and lambda 2 state innately is injected by a laser source with lambda 1 state. When the injection power exceeds the threshold power, the dominant state of the QD VCSEL changes from lambda 2 to lambda 1 state. Results of this study demonstrate that the wavelength switching based on a 1.3 mu m QD VCSEL has a simpler and more cost-effective configuration than those of previous systems.
Wire-like characteristics in stacked InAs/GaAs quantum dot superlattices for optoelectronic devices
(2007-09-01)
Chen, T. T.
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Chen, Y. F.
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Wang, J. S.
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Huang, Y. S.
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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.