Browsing by Author "Lee, C. P."

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2-3 mu m mid infrared light sources using InGaAs/GaAsSb "W" type quantum wells on InP substrates
(2010-11-15)
Pan, C. H.
;
Lin, S. D.
;
Lee, C. P.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We have investigated the InGaAs/GaAsSb/InAlGaAs/InAlAs type-II "W" quantum wells (QWs) grown on InP substrates by molecular beam epitaxy. The photoluminescence (PL) emission wavelength longer than 2.56 mu m at room temperature (RT) is demonstrated for the first time in this material system. The PL emission peaks of our designed samples can cover a wide range from 2 to 2.5 mu m at cryogenic temperature. The samples show good optical quality that the reduction in integrated PL intensity is only around one order of magnitude from 35 K to RT. We found that the integrated PL intensity decreased as the emission wavelength increased, which is due to the reduction in the electron-hole wave function overlap. This is consistent with the calculated result. In the power dependent PL measurements, the emission peak of "W" type QWs show blue shifts with the excitation power (P-ex) but does not follow the P-ex(1/3) rule as predicted by type-II band bending model. The localized states filling effect gives reasonable explanations for the observed phenomena. (C) 2010 American Institute of Physics. [doi:10.1063/1.3506427]
2-3 mu m mid infrared light sources using InGaAs/GaAsSb "W" type quantum wells on InP substrates
(2010-11-15)
Pan, C. H.
;
Lin, S. D.
;
Lee, C. P.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We have investigated the InGaAs/GaAsSb/InAlGaAs/InAlAs type-II "W" quantum wells (QWs) grown on InP substrates by molecular beam epitaxy. The photoluminescence (PL) emission wavelength longer than 2.56 mu m at room temperature (RT) is demonstrated for the first time in this material system. The PL emission peaks of our designed samples can cover a wide range from 2 to 2.5 mu m at cryogenic temperature. The samples show good optical quality that the reduction in integrated PL intensity is only around one order of magnitude from 35 K to RT. We found that the integrated PL intensity decreased as the emission wavelength increased, which is due to the reduction in the electron-hole wave function overlap. This is consistent with the calculated result. In the power dependent PL measurements, the emission peak of "W" type QWs show blue shifts with the excitation power (P(ex)) but does not follow the P(ex)(1/3) rule as predicted by type-II band bending model. The localized states filling effect gives reasonable explanations for the observed phenomena. (C) 2010 American Institute of Physics. [doi:10.1063/1.3506427]
28V high-linearity and rugged InGaP/GaAs power HBT
(2006)
Wang, Nanlei Larry
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Ma, Wenlong
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Xu, Sarah
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Camargo, Edmar
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Sun, Xiaopeng
This paper reports on the improvement of a previously developed InGaP/GaAs HBT for 24-28V linear power operation. The improvements achieved were: application of dynamic bias circuit which improves the ACLR under WCDMA modulation; modification of device technology improving ruggedness to sustain 10:1 VSWR at 30V collector bias under P1dB driving conditions and over 6 dB of gain compression; maintenance of lifetime and reliability simultaneously. Building blocks of HBT were strung together for higher power and good scaling of performance was achieved supporting the validity of the layout approach and the thermal design. Devices delivering P-1dB = 8W under CW conditions provided ACLR = -50 dBc at 8.5 dB back-off and 16% efficiency for WCDMA signal (PAR=8.7 dB) at 2.14 GHz. Lifetime test over 3000 hours was repeated for 28V bias and 0.05mA/um(2) current density at 315 degree C junction temperature. Therefore, the InGaP/GaAs HBT technology is mature now for the high linearity power amplification.
A phenomenological model for the reliability of GaAs based heterojunction bipolar transistors
(2008-05-01)
Lee, C. P.
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Chau, F.
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Lin, B.
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Kretschmar, M.
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Ma, W.
We present a phenomenological model for the lifetime prediction of GaAs based heterojunction bipolar transistors (HBTs). Both thermal activation process and recombination enhanced defect generation process were considered phenomenologically. At high stress temperatures, the lifetime of the transistor is determined by the thermal activation process and is independent of the stress current. But at low stress temperatures, the device's lifetime is controlled by the recombination enhanced defect generation process and is dependent on the stress current. The model has been used to fit experimental data, and very reasonable agreement was obtained. The model is valid for all stress temperatures and stress currents. It provides a good guideline for projecting HBTs lifetimes using accelerated stress test. (C) 2008 American Institute of Physics.
Carrier Dynamics in InAs/GaAs Quantum Rings
(2009)
Lin, C. H.
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Ling, H. S.
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Sun, K. W.
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Lee, C. P.
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Lin, S. D.
We have investigated the temperature dependence of the carrier relaxation dynamics in InAs/GaAs self-assembled quantum rings by using the time-resolved photoluminescence technique with a time resolution of similar to 250 ps. The carrier relaxation in the QRs not only shows strong dependence on the lattice temperature, it is also significant slower than the carrier relaxation in the quantum dots at temperature above 150 K.
Characteristics of In(Ga)As quantum ring infrared photodetectors
(2009-02-01)
Ling, H. S.
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Wang, S. Y.
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Lee, C. P.
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Lo, M. C.
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電子工程學系及電子研究所
Characteristics of In(Ga)As quantum ring infrared photodetectors (QRIPs) were investigated under normal incidence configuration. Compared with quantum dot infrared photodetectors (QDIPs), QRIPs showed wider photocurrent spectra, more stable responsivity with temperature change, and lower dark current activation energy. The wide detection band comes from the transitions from the quantum ring (QR) ground states to different excited states. The shallow confinement states generate higher dark current and enhance the carrier flow between the QRs within the same QR layer. This carrier flow averages out the repulsive potential and makes QRIPs behave similarly to the quantum well infrared photodetectors instead of QDIPs. With an Al(0.27)Ga(0.73)As current blocking layer, the performance of QRIPs was greatly enhanced.
Composite metal substrate for thin film AlGaInP LED applications
(2019-04-15)
Horng, R. H.
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Sinha, Shreekant
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Lee, C. P.
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Feng, H. A.
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Chung, C. Y.
The fabrication and feasibility assessment of n-side up, thin-epilayer, AlGaInPbased vertical light-emitting-diodes (LEDs; emitting area: 1 mm x 1 mm) with a copperinvar-copper-composite metal (CIC) substrate was obtained by wafer bonding and epilayer transferring technologies. The structure of CIC substrate is a top Cu layer of 20 mu m, a middle Invar layer of 64 mu m, and a bottom Cu layer of 20 mu m. The invar layer consists of Fe and Ni at a ratio of 70% to 30%. The coefficient of thermal expansion for CIC is about 6.1 x 10(-6) /K, which is similar to that of the GaAs substrate (5.7 x 10(-6)/K) and AlGaInP epilayers. Due to the high thermal conductivity (160 W/m-K) of 10(4)-mu m-thick CIC, the high performances of the packaged LEDs are obtained. They present a low red shift phenomenon (from 623 to 642 nm for 100 mA to 1 A) and a high output power 212 mW at 800 mA. The CIC substrate can be extended to fabricate high-efficiency thin film LEDs with conventional vertical electrodes. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Compositional grading in GaAsSb grown on GaAs substrates
(2014-09-15)
Lin, Y. M.
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Chen, C. H.
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Wu, J. S.
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Lee, C. P.
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電子工程學系及電子研究所
The composition profile and lattice strain of GaAsSb grown on GaAs substrates by molecular beam epitaxy have been investigated using the Rutherford backscattering spectrometry (RBS) and X-ray reciprocal space mapping. Through RBS, we found that the Sb content in the layer increases from the interface to the top surface. The X-ray reciprocal space mapping shows that the GaAsSb lattice also gradually relaxes as the layer becomes thicker. The behavior of composition grading and gradual lattice relaxation is quite different from those of III-V ternary compounds with two group Ill atoms. (C) 2014 Elsevier B.V. All rights reserved.
Compositional grading in GaAsSb grown on GaAs substrates
(2014-09-15)
Lin, Y. M.
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Chen, C. H.
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Wu, J. S.
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Lee, C. P.
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電子工程學系及電子研究所
The composition profile and lattice strain of GaAsSb grown on GaAs substrates by molecular beam epitaxy have been investigated using the Rutherford backscattering spectrometry (RBS) and X-ray reciprocal space mapping. Through RBS, we found that the Sb content in the layer increases from the interface to the top surface. The X-ray reciprocal space mapping shows that the GaAsSb lattice also gradually relaxes as the layer becomes thicker. The behavior of composition grading and gradual lattice relaxation is quite different from those of III-V ternary compounds with two group Ill atoms. (C) 2014 Elsevier B.V. All rights reserved.
Confinement-enhanced dots-in-a-well QDIPs with operating temperature over 200 K
(2009-11-01)
Ling, H. S.
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Wang, S. Y.
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Lee, C. P.
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Lo, M. C.
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電子工程學系及電子研究所
LWIR InAs/Al(0.3)Ga(0.7)As/In(0.15)Ga(0.85)As confinement-enhanced DWELL (CE-DWELL) QDIPs with operation temperatures higher than 200 K are reported. A thin Al(0.3)Ga(0.7)As barrier layer was inserted above the InAs QDs to improve the confinement of QD states in the In(0.15)Ga(0.85)As DWELL structure and the device performance. The better confinement of the electronic states increases the oscillator strength of the infrared absorption. The higher excited state energy also improves the escape probability of the photoelectrons. Compared with the conventional DWELL QDIPs, the quantum efficiency increases for more than 20 times and the detectivity is an order of magnitude higher at 77 K. With better device parameters of CE-DWELL, it is possible to achieve high quantum efficiency, high operating temperature and long wavelength detection at the same time. (C) 2009 Elsevier B.V. All rights reserved.
Design and modeling of InP-based InGaAs/GaAsSb type-II "W" type quantum wells for mid-Infrared laser applications
(2013-01-28)
Pan, C. H.
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Lee, C. P.
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
We have theoretically studied the InP based InGaAs/GaAsSb /InAlAs type-II "W" quantum wells (QWs) using the eight band k.p theory. The trade-off between the emission wavelength and the magnitude of the transition matrix element was investigated with various structural parameters of the "W" QWs. For the same emission wavelength, the devices with thinner InGaAs/GaAsSb layers and a higher Sb content in GaAsSb could provide higher transition strength. The gain spectra and their peak values at various carrier densities were calculated. We have also found that a more balanced electron and hole masses in the type-II "W" QWs can benefit the material gain. In our designed cases, we have seen that the reduced hole effective mass due to a higher Sb content can partially compensate the gain loss caused by the reduced transition matrix element. Based on the optimized design, a material gain above 10(3) cm(-1) is readily achievable for a single properly designed "W" quantum well. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789634]
Detection wavelength and device performance tuning of InAs QDIPs with thin AlGaAs layers
(2009-11-01)
Wang, S. Y.
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Ling, H. S.
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Lo, M. C.
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Lee, C. P.
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電子工程學系及電子研究所
QDIPs with thin inserted AlGaAs layers adjacent to the QDs were investigated for the tailoring of detection wavelength and device performance. Simple InAs/GaAs QDIPs and DWELL QDIPs with different insertion layer structure were studied. The thin AlGaAs layer is shown to effectively modify the electron wavefunction and associated confined state energies which lead to the change of the detection wavelength and the polarization dependent quantum efficiency. Furthermore. the dark current and gain also change with different device structures. The insertion of AlGaAs layers provides an additional freedom of tuning the electronics states involved in the infrared detection and also enables the improvement of the absorption and device performance. (C) 2009 Elsevier B.V. All rights reserved.
Edge magnetoplasma excitations in quantum wire arrays
(2008-03-01)
Hsieh, W. H.
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Suen, Y. W.
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Lee, B. C.
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Li, L. C.
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Lee, C. P.
We report the low-temperature microwave properties of edge magneto-plasma excitations in quantum-wire arrays, fabricated from a two-dimensional electron gas in a GaAs/AlGaAs heterostructure and embedded in the slots of a 50-Omega meandering coplanar waveguide. The plot of frequency versus Landau level filling factors with strong absorption gives a series of barn-shaped curves with tops being centered in the quantum Hall effect plateaus and following a straight line through the origin. Away from the plateau center, the absorption dip becomes weaker and disappears near the plateau-plateau transition regime, qualitatively following the magneto hydrodynamic model. At frequencies above this barn-shaped part, however, we also observed unexpected resonant dips. (c) 2007 Published by Elsevier B.V.
Effect of double heterojunctions on the plasmon-phonon coupling in a GaAs/Al(0.24)Ga(0.76)As quantum well
(2008-12-01)
Lee, H. C.
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Sun, K. W.
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Lee, C. P.
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應用化學系
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電子工程學系及電子研究所
Quasi-two-dimensional (Q2D) Coulomb interactions between plasmons and phonons in a GaAs quantum well are studied numerically. Based on the dielectric continuum model, the plasmon-confined phonon coupling and plasmon-symmetric (+/-) interface phonon coupling are considered. By using renormalized phonon propagators, six branches involving plasmon-like and phonon-like modes are obtained and used to study the effect on the hot-carrier average energy-loss rate (AELR). Plasmon-like modes are demonstrated to enhance the AELR around the sheet carrier density of 10(11) cm(-2) due to a significant contribution of the plasmon-symmetric (+) interface phonon coupled mode. The importance of interface phonon modes on the plasmon-phonon coupling (PPC) is also indicated. If the interface phonon is not considered, the AELR enhancement due to the PPC will not appear. In addition, the carrier temperature is found to be important for the AELR enhancement. As the carrier temperature is as low as possible, the AELR enhances more remarkably because the effect of reabsorption of plasmon-like modes for hot carriers (hot-plasmon effect) can be greatly suppressed.
Effect of interfacial layer on the crystal structure of InAs/AlAs0.16Sb0.84/AlSb quantum wells
(2014-04-28)
Lin, Y. M.
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Chen, C. H.
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Lee, C. P.
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電子工程學系及電子研究所
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奈米科技中心
Ion channeling technique using MeV C2+ ions and high resolution X-ray diffraction were used to study the crystal quality of an InAs/AlSb-based quantum wells. We found that the InAs quality has a strong dependence on the type of the interface used. With the addition of the InSb-like interface, the crystal quality of the InAs channel was greatly improved. The InAs lattice was fully strained and aligned with the lattice of the buffer layer without any lattice relaxation. On the other hand, if the interface was of the AlAs type, the lattice of the InAs quantum well was relaxed and the crystal quality was poor. This explains why a superior InAs quantum well with high electron mobility and good surface morphology can be achieved with the use of the InSb interface. (C) 2014 AIP Publishing LLC.
Effect of the electromagnetic environment on the dynamics of charge and phase particles in one-dimensional arrays of small Josephson junctions
(2011-11-01)
Ho, I. L.
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Kuo, W.
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Lin, S. D.
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Lee, C. P.
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Liang, C. T.
The effect of the electromagnetic environment on the dynamics of quasi-particles, Cooper pairs and phase particles in one-dimensional arrays of small Josephson junctions is investigated experimentally and theoretically. It is found that the environment enhances the phase ordering and thus suppresses quasi-particle tunneling at high temperature and localization of Cooper pairs at low temperature. The dynamics is studied in the context of phase-charge duality, and the experimental results are quantitatively analyzed in both charge-ordered and phase-ordered regimes. Based on these analyses, a low-temperature phase diagram as well as a finite-temperature crossover phase diagram are constructed and compared to the experimental diagrams. Copyright (C) EPLA, 2011
Efficiency of quantum dot solar cell enhanced by improving quantum dots performance
(2015-02-01)
Weng, H. L.
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Ueng, H. Y.
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Lee, C. P.
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
We propose an innovative description to provide a quantitative basis to enhance the conversion efficiency of InAs/GaAs quantum dot solar cells (QDSC). A theoretical approach and numerical simulation are used to improve the performance of the quantum dots and analyze the relevance to enhance the conversion efficiency. The absorption coefficient of QDs is determined in terms of dot material, dot size, size dispersion, and shape, which are used to obtain a better match between the absorption spectrum of QDs with the portion of the solar spectrum. Either increasing the surface density for raising the photocurrent or enlarging the dot size for matching well the solar spectrum is a trade-off issue. The influence of surface density, spacer thickness, and number of dot layers on the open-circuit voltage and efficiency is discussed in detail. Moreover, volume fraction can be taken as a balance reference for the counteracting effect between J(SC) and V-OC.
Electrical characteristics of Ni Ohmic contact on n-type GeSn
(2014-06-16)
Li, H.
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Cheng, H. H.
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Lee, L. C.
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Lee, C. P.
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Su, L. H.
We report an investigation of the electrical and material characteristics of Ni on an n-type GeSn film under thermal annealing. The current-voltage traces measured with the transmission line method are linear for a wide range of annealing temperatures. The specific contact resistivity was found to decrease with increasing annealing temperature, followed by an increase as the annealing temperature further increased, with a minimum value at an annealing temperature of 350 degrees C. The material characteristics at the interface layer were measured by energy-dispersive spectrometer, showing that an atomic ratio of (Ni)/(GeSn) = 1:1 yields the lowest specific contact resistivity. (C) 2014 AIP Publishing LLC.
Electron delocalization of tensily strained GaAs quantum dots in GaSb matrix
(2010-12-15)
Lin, T. C.
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Wu, Y. H.
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Li, L. C.
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Sung, Y. T.
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Lin, S. D.
The magneto-optical response of type-II tensily strained GaAs self-assembled quantum dots in GaSb was investigated in magnetic fields up to 14 T. By depositing different GaAs amount, the dot sizes and the corresponding emission energies were varied. We analyzed the carrier wave function extent of different dots using the diamagnetic shift results. It was found that, with the increase in the energy (the reduction in the dot size), the diamagnetic coefficient first rises quickly and then saturates at around 21 mu eV/T(2). Based on a simple calculation model, this unusual tendency is attributed to the electrons gradually spilling out of the quantum dot to the wetting layer as the dots get smaller. This delocalization effect is enhanced in this material system due to the tensile strain relaxation within the dots, which raises the conduction band edge over that in the wetting layer. (c) 2010 American Institute of Physics. [doi: 10.1063/1.3520669]
Energy dependent carrier relaxation in self-assembled InAs/GaAs quantum dots
(2008)
Ling, H. S.
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Lee, C. P.
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Wang, S. Y.
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Lo, M. C.
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電子工程學系及電子研究所
We performed the selective excitation photoluminescence (SEPL) spectroscopy studies on InAs/GaAs self-assembled quantum dots (QDs). Under different excitation energies, different groups of QDs are selected and emit light. The excited carriers relax to the ground state through different mechanisms when excited at different energies. Three distinct regions with different mechanisms in carrier excitations and relaxation are identified in the emission spectra. These three regions can be categorized, from high energy to low energy, as continuum absorption, electronic state excitation, and multi-phonon resonance. The QDs special joint density-of-state tail extending from the wetting layer peak facilitates the carrier relaxation and was suggested to explain these spectral results. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.