Search Results - (Author, Cooperation:H. K. Choi)

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  1. 1
    Staff View
    Publication Date:
    2018-03-09
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    1098-0121
    Electronic ISSN:
    1095-3795
    Topics:
    Physics
    Keywords:
    Surface physics, nanoscale physics, low-dimensional systems
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Y. Okada ; D. Wu ; G. Trynka ; T. Raj ; C. Terao ; K. Ikari ; Y. Kochi ; K. Ohmura ; A. Suzuki ; S. Yoshida ; R. R. Graham ; A. Manoharan ; W. Ortmann ; T. Bhangale ; J. C. Denny ; R. J. Carroll ; A. E. Eyler ; J. D. Greenberg ; J. M. Kremer ; D. A. Pappas ; L. Jiang ; J. Yin ; L. Ye ; D. F. Su ; J. Yang ; G. Xie ; E. Keystone ; H. J. Westra ; T. Esko ; A. Metspalu ; X. Zhou ; N. Gupta ; D. Mirel ; E. A. Stahl ; D. Diogo ; J. Cui ; K. Liao ; M. H. Guo ; K. Myouzen ; T. Kawaguchi ; M. J. Coenen ; P. L. van Riel ; M. A. van de Laar ; H. J. Guchelaar ; T. W. Huizinga ; P. Dieude ; X. Mariette ; S. L. Bridges, Jr. ; A. Zhernakova ; R. E. Toes ; P. P. Tak ; C. Miceli-Richard ; S. Y. Bang ; H. S. Lee ; J. Martin ; M. A. Gonzalez-Gay ; L. Rodriguez-Rodriguez ; S. Rantapaa-Dahlqvist ; L. Arlestig ; H. K. Choi ; Y. Kamatani ; P. Galan ; M. Lathrop ; S. Eyre ; J. Bowes ; A. Barton ; N. de Vries ; L. W. Moreland ; L. A. Criswell ; E. W. Karlson ; A. Taniguchi ; R. Yamada ; M. Kubo ; J. S. Liu ; S. C. Bae ; J. Worthington ; L. Padyukov ; L. Klareskog ; P. K. Gregersen ; S. Raychaudhuri ; B. E. Stranger ; P. L. De Jager ; L. Franke ; P. M. Visscher ; M. A. Brown ; H. Yamanaka ; T. Mimori ; A. Takahashi ; H. Xu ; T. W. Behrens ; K. A. Siminovitch ; S. Momohara ; F. Matsuda ; K. Yamamoto ; R. M. Plenge
    Nature Publishing Group (NPG)
    Published 2014
    Staff View
    Publication Date:
    2014-01-07
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Alleles ; Animals ; Arthritis, Rheumatoid/*drug therapy/*genetics/metabolism/pathology ; Asian Continental Ancestry Group/genetics ; Case-Control Studies ; Computational Biology ; *Drug Discovery ; Drug Repositioning ; European Continental Ancestry Group/genetics ; Female ; Genetic Predisposition to Disease/*genetics ; Genome-Wide Association Study ; Hematologic Neoplasms/genetics/metabolism ; Humans ; Male ; Mice ; Mice, Knockout ; *Molecular Targeted Therapy ; Polymorphism, Single Nucleotide/genetics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  3. 3
    E. Weisz ; H. K. Choi ; I. Sivan ; M. Heiblum ; Y. Gefen ; D. Mahalu ; V. Umansky
    American Association for the Advancement of Science (AAAS)
    Published 2014
    Staff View
    Publication Date:
    2014-06-21
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  4. 4
    Staff View
    Publication Date:
    2018-02-08
    Publisher:
    Institute of Physics (IOP)
    Print ISSN:
    1757-8981
    Electronic ISSN:
    1757-899X
    Topics:
    Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by:
    http://www.iop.org/

    Latest Papers from Table of Contents or Articles in Press
  5. 5
    Staff View
    Publication Date:
    2018-02-08
    Publisher:
    Institute of Physics (IOP)
    Print ISSN:
    1757-8981
    Electronic ISSN:
    1757-899X
    Topics:
    Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by:
    http://www.iop.org/

    Latest Papers from Table of Contents or Articles in Press
  6. 6
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Coherent cw operation of a 10×10×2 grating-surface-emitting diode laser array in a ring configuration is demonstrated. At near twice the threshold current, the ring array exhibits a high degree of spatial coherence (an average of 86%) between emitting grating sections and a narrow linewidth of 28 MHz. The far field fringe visibility is 80% and 88% in the lateral and longitudinal directions, respectively.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.350363

    Articles: DFG German National Licenses
  7. 7
    Choi, H. K. ; Wang, C. A. ; Fan, John C. C.

    [S.l.] : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs diode lasers exhibiting continuous (cw) operation at room temperature have been grown on a Si substrate by organometallic vapor-phase epitaxy, without the use of molecular-beam epitaxy. To improve the quality of the laser structure, a defect-filtering layer was incorporated between this structure and a GaAs buffer layer about 1.5 μm thick grown on the substrate. Of four types of defect-filtering layers investigated, the most effective was one grown with thermal cycling, which made it possible to obtain pulsed threshold current densities as low as 350 A/cm2 for broad-stripe lasers with a cavity length of 500 μm. Ridge-waveguide lasers with this type of defect-filtering layer have exhibited cw threshold currents as low as 25 mA and a differential quantum efficiency of 55%.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.346583

    Articles: DFG German National Licenses
  8. 8
    Wang, C. A. ; Walpole, J. N. ; Missaggia, L. J. ; Donnelly, J. P. ; Choi, H. K.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Separate-confinement heterostructure diode lasers containing a strained Al0.18In0.20Ga0.62 As single quantum well active layer and Al0.25Ga0.75As confining layers have been fabricated from structures grown on GaAs substrates by low-pressure organometallic vapor phase epitaxy. The emission wavelength of these devices is 814 nm. Threshold current density is as low as 103 A cm−2 for cavity length L=1500 μm, and differential quantum efficiency as high as 90% for L=280 μm. The characteristic temperature T0 is 214 K between 10 and 40 °C, and 159 K between 40 and 80 °C. Preliminary tests of cw operation suggest that these lasers are more reliable than AlGaAs/AlGaAs lasers.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.104928

    Articles: DFG German National Licenses
  9. 9
    Choi, H. K. ; Eglash, S. J.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Gain-guided Ga0.84In0.16As0.14Sb0.86/Al0.75 Ga0.25As0.06Sb0.94 double-heterostructure lasers emitting at ∼2.2 μm have been operated cw at heat sink temperatures up to 30 °C. The maximum output powers obtained at 5 and 20 °C were 10.5 and 4.6 mW/facet, respectively. For pulsed operation of broad-stripe lasers 300 μm wide and 1000 μm long, the threshold current density was as low as 940 A/cm2, the lowest room-temperature value reported for diode lasers emitting beyond 2 μm.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.105544

    Articles: DFG German National Licenses
  10. 10
    Wang, C. A. ; Choi, H. K.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1997
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A GaInAsSb/AlGaAsSb multiple-quantum-well diode laser structure consisting of Al0.6Ga0.4As0.05Sb0.95 cladding layers, Al0.3Ga0.7As0.02Sb0.98 confining layers, and four 15-nm-thick Ga0.87In0.13As0.12Sb0.88 quantum wells with 20-nm-thick Al0.3Ga0.7As0.02Sb0.98 barrier layers was grown by organometallic vapor phase epitaxy. These lasers, emitting at 2.1 μm, have exhibited pulsed threshold current densities as low as 1.2 kA/cm2. © 1997 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.118227

    Articles: DFG German National Licenses
  11. 11
    Choi, H. K. ; Wang, C. A.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Graded-index separate-confinement heterostructure InGaAs/AlGaAs single quantum well diode lasers emitting at 1.02 μm have been fabricated from structures grown by organometallic vapor phase epitaxy. Under pulsed operation, threshold current densities as low as 65 A/cm2, the lowest reported for InGaAs/AsGaAs lasers, have been obtained for a cavity length L of 1500 μm. Differential quantum efficiencies as high as 90% have been obtained for L=300 μm. Output powers as high as 1.6 W per facet and power conversion efficiencies as high as 47% have been obtained for continuous operation of uncoated lasers with L=1000 μm.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.103678

    Articles: DFG German National Licenses
  12. 12
    Eglash, S. J. ; Choi, H. K.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Diode lasers emitting at 2.29 μm have been fabricated from lattice-matched double heterostructures having a GaInAsSb active layer and AlGaAsSb confining layers grown by molecular beam epitaxy on GaSb substrates. For pulsed room-temperature operation these devices have exhibited threshold current densities as low as 1.7 kA/cm2 and differential quantum efficiencies as high as 18% per facet, the highest room-temperature efficiency reported for any semiconductor diode laser emitting beyond 2 μm.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.103462

    Articles: DFG German National Licenses
  13. 13
    Le, H. Q. ; Choi, H. K. ; Wang, C. A.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The two-photon absorption (TPA) coefficient has been measured for a single-mode GaAs/AlGaAs quantum well laser at 0.86 μm, near the lasing wavelength of 0.83 μm. Picosecond laser pulses were employed to resolve the ultrafast TPA from long-lived carrier-dependent effects. The TPA coefficient was found to be 31±6 cm GW−1, which corresponds to a value of (5.7±1.2)×10−11 esu for the imaginary part of the third-order nonlinear susceptibility. At wavelengths near the quantum well exciton, no strong resonance enhancement of the two-photon transition was observed, and the coefficient appears to be characteristic of the AlGaAs cladding layers.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.103741

    Articles: DFG German National Licenses
  14. 14
    Choi, H. K. ; Lee, J. W. ; Salerno, J. P. ; Connors, M. K. ; Tsaur, B-Y. ; Fan, J. C. C.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Low-threshold double-heterostructure ridge-waveguide lasers have been fabricated in GaAs/AlGaAs layers grown on Si by organometallic vapor phase epitaxy. The pulsed threshold current of the best ridge-waveguide laser is 50 mA, with differential quantum efficiency of about 9% per facet. Broad-area lasers fabricated on the same wafer have pulsed threshold current densities as low as 300 A/cm2 .
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.99178

    Articles: DFG German National Licenses
  15. 15
    Choi, H. K. ; Turner, G. W. ; Liau, Z. L.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1994
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Double-heterostructure diode lasers emitting at ∼3.9 μm have exhibited pulsed operation at temperatures up to 170 K and cw operation up to 105 K, with single-ended cw output power of 30 mW at 70 K. The laser structure, grown on GaSb substrates by molecular-beam epitaxy, has an InAsSb active layer and AlAsSb cladding layers. The lowest pulsed threshold current density is 36 A/cm2 obtained at 60 K. The characteristic temperature is 20 K over the entire temperature range. © 1994 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.112779

    Articles: DFG German National Licenses
  16. 16
    Liau, Z. L. ; Choi, H. K.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1994
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A new strained-layer multiple-quantum-well (MQW) heterostructure comprising InAs1−xSbx wells and In1−yGayAs barrier layers is proposed for improved 4–5 μm lasers. Both well and barrier compositions are close to InAs and are potentially well suited for high-quality crystal growth of MQWs on either InAs or GaSb substrates. Simple modeling shows favorable valence-band alignment suitable for carrier confinement, free of the staggered band alignment problem generally found in the conventional designs. Perturbation calculation of the effect of the compressive strain in the wells also shows sufficient valence subband separation. This and the reduced hole mass are expected to considerably lower the threshold carrier density and Auger recombination.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.111341

    Articles: DFG German National Licenses
  17. 17
    Sun, C.-K. ; Choi, H. K. ; Wang, C. A. ; Fujimoto, J. G.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Carrier heating processes in InGaAs/AlGaAs strained-layer single-quantum well devices are studied by using a new femtosecond multiple-wavelength pump probe technique. Contributions from free-carrier absorption and stimulated transitions have been separated by using different combinations of pump and probe wavelengths above and below the band gap. Different cooling times were measured which reflect different thermalization mechanisms. Results show that free-carrier absorption is not always the dominant carrier heating process in III-V quantum well devices.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.108594

    Articles: DFG German National Licenses
  18. 18
    Choi, H. K. ; Eglash, S. J. ; Connors, M. K.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Ridge-waveguide lasers emitting at ∼2.1 μm have been fabricated from a GaInAsSb/AlGaAsSb quantum-well heterostructure grown on a GaSb substrate by molecular beam epitaxy. The cw threshold current is as low as 29 mA at room temperature, and the maximum cw output power is 28 mW. The lasers operate in a single longitudinal mode which can be continuously tuned without mode hopping over 1.2 nm by changing the heatsink temperature and over 0.8 nm by changing the current.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.110171

    Articles: DFG German National Licenses
  19. 19
    Choi, H. K. ; Eglash, S. J.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1992
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The first GaInAsSb/AlGaAsSb diode lasers with a quantum-well active region have been demonstrated. These devices, which were grown by molecular beam epitaxy, emit at ∼2.1 μm. For room-temperature pulsed operation of lasers 100 μm wide, threshold current density as low as 260 A/cm2 and differential quantum efficiency up to 70% have been obtained for cavity lengths of 2000 and 300 μm, respectively. One device 100 μm wide and 1000 μm long has operated pulsed at heatsink temperatures up to 150 °C, with a characteristic temperature of 113 K between 20 and 40 °C. For another device of the same dimensions, cw output power up to 190 mW/facet has been achieved at a heatsink temperature of 20 °C. These characteristics represent a dramatic improvement in performance over double-heterostructure GaInAsSb/AlGaAsSb diode lasers.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.107630

    Articles: DFG German National Licenses
  20. 20
    Choi, H. K. ; Wang, C. A. ; Karam, N. H.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Strained InGaAs/AlGaAs quantum well diode lasers have been fabricated on Si substrates for the first time. A GaAs buffer layer was grown on each Si wafer by temperature-cycled organometallic vapor phase epitaxy (OMVPE). The wafer was then transferred to a second reactor for OMVPE growth of a graded-index separate-confinement heterostructure single-quantum well laser structure. For lasers with a cavity length of 1000 μm, room-temperature pulsed threshold current densities as low as 174 and 195 A/cm2 have been obtained for active layer compositions of In0.02Ga0.98As and In0.05Ga0.95As, respectively. One laser with an In0.05Ga0.95As active layer operated cw for 56.5 h, a record lifetime for GaAs-based diode lasers on Si.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.105921

    Articles: DFG German National Licenses