H. K. Choi

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (105)162.67 Total impact

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    ABSTRACT: By improving the thermal uniformity and stability of our graphite-strip-heater oven, we have been able to significantly improve the overall quality of ZMR Si films. We have observed unbranched subboundaries and new types of defects that are less extended than the usual sub-boundaries. The overall wafer flatness has been improved so that total warp is less than 4 μm for 3-inch wafers. We have also utilized the ZMR technique for producing thin Ge-on-insulator films. How to Cite This Article Link to This Abstract Blog This Article Copy and paste this link Highlight all http://dx.doi.org/10.1557/PROC-35-613 Citation is provided in standard text and BibTeX formats below. Highlight all BibTeX Format @inproceedings{OPL:8145164,author = {Chen,C. K. and Gels,M. W. and Choi,H. K. and Tsaur,B-Y. and Fan,John C. C.},title = {Recent Advances in Si And Ge Zone-Melting Recrystallization},booktitle = {Symposium A – Energy Beam-Solid Interactions and Transient Thermal Processing/1984},series = {MRS Proceedings},volume = {35},year = {1984},doi = {10.1557/PROC-35-613},URL = {http://journals.cambridge.org/article_S1946427400405129},} Click here for full citation export options. Blog This Article Blog This Article : Highlight all Recent Advances in Si And Ge Zone-Melting Recrystallization C. K. Chen,M. W. Gels,H. K. Choi,B-Y. Tsaur and John C. C. Fan (1984). MRS Proceedings , Volume 35 , 1984, 613 http://journals.cambridge.org/action/displayAbstract?aid=8145164 The code will display like this Recent Advances in Si And Ge Zone-Melting Recrystallization C. K. Chen, M. W. Gels, H. K. Choi, B-Y. Tsaur and John C. C. Fan 1984 MRS Proceedings, ,Volume35, 1984, 613 http://journals.cambridge.org/abstract_S1946427400405129 C. K. Chen, M. W. Gels, H. K. Choi, B-Y. Tsaur and John C. C. Fan (1984). Recent Advances in Si And Ge Zone-Melting Recrystallization. MRS Proceedings, 35, 613 doi:10.1557/PROC-35-613. 0Comments
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • H. K. Choi · G. W. Turner · B-Y. Tsaur
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    ABSTRACT: The status of monolithic GaAs/Si (MGS) integration is reviewed and its future prospects are discussed. The MGS material now available is satisfactory for majority-carrier devices, but improvement in quality is needed for minority-carrier devices. By using a suitable sequence of processing steps, fabrication of GaAs MESFETs and Si MOSFETs on the same wafer and monolithic integration of GaAs/AlGaAs double-heterostructure LEDs and Si MOSFETs have been achieved. The GaAs and Si FETs show characteristics comparable to those for devices fabricated on separate GaAs and Si substrates. The LEDs have been modulated up to 27 Mb/s by applying a pattern of voltage pulses to the MOSFET gate. Two promising applications of MGS integration are optical interconnects between Si VLSI chips and monolithic microwave integrated circuits. Much better performance should be obtained by operating MGS ICs at liquid nitrogen temperature.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Mid-infrared optically pumped semiconductor lasers (OPSLs) are presently being investigated for a variety of commercial and military applications. Active regions in such optically pumped lasers must meet the dual requirements of high gain and low loss at mid-IR wavelengths, combined with sufficient absorption of the optical pump at shorter wavelengths for efficient power conversion. In this paper we report the successful growth, fabrication, and characterization of high-performance OPSLs that employ novel active regions consisting of combinations of GalnAsSb integrated-absorber layers with type-II GaInSb/InAs quantum well regions. With 1.85-µm optical pumping at 85 K, OPSLs with such active regions have exhibited a peak output power of 2.1 W at 3.9 pm, improved beam quality, power conversion efficiency of ∼8%, and characteristic temperatures of ∼47 K.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: High‐performance GaInAsSb/AlGaAsSb/GaSb thermophotovoltaic (TPV) devices with quantum efficiency and fill factor near theoretical limits and open‐circuit voltage within about 15% of the limit are reported. This paper discusses detailed studies of GaInAsSb epitaxial growth, the microstructure, and minority carrier lifetime that have led to these results. For further improvements in TPV cell performance, device structures with either a distributed Bragg reflector or a back‐surface reflector are described.
    No preview · Article · Jan 2003
  • C.A. Wang · H.K. Choi · G.W. Charache
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    ABSTRACT: The growth and characterisation of GaInAsSb alloys, lattice-matched to GaSb substrates, are reported, with a particular focus on these alloys for thermophotovoltaic (TPV) devices. Using a unique combination of organometallic precursors, high-quality metastable GaInAsSb epitaxial layers with energy gaps as low as 0.5 eV have been grown by organometallic vapour-phase epitaxy. The GaInAsSb material quality is significantly improved for growth at a lower growth temperature of 525°C compared with 575°C, and at a higher growth rate of 5 μm/h compared with 1.2 μm/h. 4 K photoluminescence full width at half maximum values are as low as 4.3 meV for 0.59 eV GaInAsSb and 9.5 meV for 0.5 eV GaInAsSb. The importance of the surface step structure and growth kinetics on these metastable alloys is discussed. Uncoated TPV devices incorporating metastable GaInAsSb, with energy gaps in the range 0.495-0.549 eV, and a GaSb window layer exhibit an external quantum efficiency (QE) of nearly 60%, which corresponds to an internal QE of 90%. The open-circuit voltage is 313 mV for the 0.549 eV device, and decreases to 239 mV for the 0.495 eV device
    No preview · Article · Jul 2000 · IEE Proceedings - Optoelectronics
  • Source
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    ABSTRACT: Recent progress in tapered high-brightness lasers emitting in the near infrared region from 1.3 to 2.0 tm is reviewed. Improved power and beam quality are obtained for tapered lasers operating near 1.55 jtm using Gaussian distributed lateral carrier injection profiles. Results for high-brightness 9-element arrays of tapered lasers emitting near 2.0 im are included. Also included is a discussion of the use of mass-transported microlenses for collimating the output of the astigmatic tapered devices and coupling them into optical fibers.
    Preview · Article · Apr 2000 · Proceedings of SPIE - The International Society for Optical Engineering
  • V Daneu · A Sanchez · T.Y. Fan · H K Choi · G W Turner · C C Cook
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    ABSTRACT: The outputs from an 11-element, linear diode laser array with broad stripes have been beam combined into a single beam with a beam quality of ~20x diffraction limited in the plane of the junction. This beam combining was achieved by use of a common external cavity containing a grating, which simultaneously forces each array element to operate at a different, but controlled, wavelength and forces the beams from all the elements to overlap and propagate in the same direction. The power in the combined beam was 50% of the output from the bare laser array.
    No preview · Article · Apr 2000 · Optics Letters
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    ABSTRACT: Summary form only given. We believe we report the first demonstration of high-power GaInSb-InAs type-II QW lasers incorporating GaInAsSb absorber layers. To ensure good carrier transport from the absorber layers to the active wells, the absorber layers were inserted between each active well region
    No preview · Conference Paper · Feb 2000
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    ABSTRACT: We report on a 4 μm, optically-pumped, Sb-based laser design which allows for the optimization of the active gain region for high temperature operation while preserving high-efficiency and good beam quality. For optically pumped Sb-based lasers operating at 4 μm, the highest efficiency under long-pulse conditions (>25 μs) was reported for an InAsSb-AlAsSb double-heterostructure (DH) laser pumped by 1.9 μm diode lasers
    No preview · Conference Paper · Feb 2000
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    ABSTRACT: Linear arrays of GaInAsSb-AlGaAsSb tapered MQW lasers emitting at 2.05 /spl mu/m have been fabricated and operated with 1-ms current pulses. Peak power over 3 W was obtained for nine-element arrays at 18.5 A. Up to 1.7-W peak power, within a 65-mrad full-angle cone, was measured in the far field using anamorphic collimating lens arrays, fabricated by mass transport in GaP.
    No preview · Article · Nov 1999 · IEEE Photonics Technology Letters
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    ABSTRACT: We report high-performance lattice-matched GaInAsSb/GaSb thermophotovoltaic (TPV) devices with a 0.5 eV band gap. The TPV structures were grown on GaSb substrates by organometallic vapor phase epitaxy at a lower temperature (525 °C compared to 550 °C) to improve the quality of the metastable GaInAsSb alloy. The 0.5 eV TPV devices exhibit external quantum efficiency as high as 60%, which corresponds to an internal quantum efficiency of 90%, assuming 35% reflection losses. This efficiency is comparable to the value measured for 0.53 eV devices. The ratio of the open circuit voltage to band-gap energy ratio decreases from 0.57 for 0.53 eV devices to 0.48 for 0.5 eV devices. © 1999 American Institute of Physics.
    No preview · Article · Aug 1999 · Applied Physics Letters
  • C. A. Wang · H. K. Choi · D. C. Oakley · G. W. Charache
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    ABSTRACT: This paper reports the growth, materials characterization, and device performance of lattice-matched GaInAsSb/GaSb thermophotovoltaic (TPV) devices with cutoff wavelength extended from 2.3 to 2.5 μm. GaInAsSb epilayers were grown lattice matched to GaSb substrates by organometallic vapor phase epitaxy using all organometallic precursors including triethylgallium, trimethylindium, tertiarybutylarsine, and trimethylantimony with diethyltellurium and dimethylzinc as the n- and p-type dopants, respectively. The growth temperature was 525 °C. Although these alloys are metastable, a mirror-like surface morphology and room-temperature photoluminescence (PL) are obtained for alloys with PL peak emission at room temperature as long as 2.5 μm. Lattice-matched GaInAsSb/GaSb TPV devices exhibit internal quantum efficiency as high as 90% for devices with a cutoff wavelength of 2.5 μm. The open circuit voltage for extended wavelength devices is 239 mV at 3.6 A/cm2. © 1999 American Institute of Physics.
    No preview · Article · Mar 1999
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    ABSTRACT: The hotside operating temperatures for many projected thermophotovoltaic (TPV) conversion system applications are approximately 1000 °C, which sets an upper limit on the TPV diode band gap of 0.6 eV from efficiency and power density considerations. This band gap requirement has necessitated the development of new diode material systems never previously considered for energy generation. To date, InGaAsSb quaternary diodes grown lattice matched on GaSb substrates have achieved the highest performance. In this article we relate observed diode performance to electro-optical properties such as minority carrier lifetime, diffusion length, and mobility and provide initial links to microstructural properties. This analysis has bounded potential diode performance improvements. For the 0.53 eV InGaAsSb diodes used in this analysis (active layer doping is 2×1017 cm−3) the dark current density measured is 2×10−5 A/cm2 versus a potential Auger and/or a radiative limit of 2×10−6 A/cm2 (no photon recycling), and an absolute thermodynamic limit of 1.4×10−7 A/cm2. These dark current limits are equivalent to open circuit voltage gains of 60 (20%) and 140 mV (45%), respectively. © 1999 American Institute of Physics.
    No preview · Article · Feb 1999 · Journal of Applied Physics
  • C.A. Wang · H.K. Choi · D.C. Oakley · G.W. Charache
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    ABSTRACT: Studies on the materials development of Ga1−xInxAsySb1−y alloys for thermophotovoltaic (TPV) devices are reported. Ga1−xInxAsySb1−y epilayers were grown lattice-matched to GaSb substrates by organometallic vapor-phase epitaxy (OMVPE) using all organometallic precursors including triethylgallium, trimethylindium, tertiarybutylarsine, and trimethylantimony with diethyltellurium and dimethylzinc as the n- and p-type dopants, respectively. The epilayer characteristics of these alloys depend on growth temperature, In and As content, V/III ratio, and substrate misorientation. A mirror-like surface morphology and room-temperature photoluminescence (PL) are obtained for GaInAsSb layers with peak emission in the wavelength range between 2 and 2.5 μm. The material properties of the metastable alloys improve for growth temperature decreasing from 575°C to 525°C and with decreasing In and As content, as based on epilayer surface morphology, X-ray diffraction, and low-temperature PL spectra. In general, GaInAsSb layers grown on (1 0 0)GaSb substrates with a 6° toward (1 1 1)B misorientation exhibit overall better material quality than layers grown on the more standard substrate (1 0 0) 2° toward (1 1 0). Consistent growth of high-performance lattice-matched GaInAsSb TPV devices is also demonstrated.
    No preview · Article · Dec 1998 · Journal of Crystal Growth
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    ABSTRACT: GaInAsSb alloys are of great interest for lattice-matched thermophotovoltaic (TPV) devices because of the high performance attainable at 2.2 {micro}m. Extension of the TPV device cutoff wavelength to beyond 2.2 {micro}m is especially desirable since the emissive power of the source is significant at these longer wavelengths. However, the GaInAsSb quaternary alloy system exhibits a miscibility gap in the wavelength range of interest, and no devices with cutoff wavelengths longer than 2.3 {micro}m have been demonstrated. This paper reports the successful growth of GaInAsSb alloys which exhibit room temperature photoluminescence (PL) at wavelengths as long as 2.5 {micro}m. TPV devices with cutoff wavelengths out to 2.5 {micro}m exhibit external quantum efficiencies of 57%. These values are comparable to those measured for 2.2 {micro}m devices.
    No preview · Article · Oct 1998
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    ABSTRACT: Thermophotovoltaic generation of electricity is attracting renewed attention due to recent advances in low bandgap (0.5–0.7 eV) III-V semiconductors. The use of these devices in a number of applications has been reviewed in a number of publications.1–4 Two potential low-bandgap diode materials are InxGa1−xAsySb1−y and InxGa1−xAs. The performance of these devices are comparable (quantum efficiency, open circuit voltage, fill factor) despite the latter’s long-term development for optoelectronics. For an 1100°C blackbody, nominally 0.55 eV devices at 25°C exhibit average photon-weighted internal quantum efficiencies of 70–80%, open circuit voltage factors of 60–65%, and fill factors of 65–70%. Equally important as the energy conversion device is the spectral control filter that effectively transmits above bandgap radiation into the diode and reflects the below bandgap radiation back to the radiator. Recent developments in spectral control technology, including InGaAs plasma filters and nonabsorbing interference filters are presented. Current tandem filters exhibit spectral utilization factors of ∼65% for an 1100°C blackbody.
    No preview · Article · Sep 1998 · Journal of Electronic Materials
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    ABSTRACT: Tapered lasers fabricated from a GaInAsSb-AlGaAsSb single-quantum-well structure are reported. The laser structure, grown by molecular beam epitaxy, has broad-stripe pulsed threshold current densities as low as 50 A/cm/sup 2/ at room temperature. Tapered lasers have exhibited diffraction-limited continuous-wave output power up to 600 mW.
    No preview · Article · Aug 1998 · IEEE Photonics Technology Letters
  • G. W. Turner · H. K. Choi · M. J. Manfra
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    ABSTRACT: Strained single-quantum-well, broadened-waveguide GaInAsSb/AlGaAsSb diode lasers have exhibited room-temperature threshold current densities as low as 50 A/cm(2), one of the lowest values reported for diode lasers at room temperature, These lasers, grown by molecular beam epitaxy, have emission wavelengths of similar to 2.05 mu m, characteristic temperature of 65 K, internal quantum efficiency of 95%, and internal loss coefficient of 7 cm(-1). Single-ended cw power of 1 W is obtained for a 100-mu m aperture. (C) 1998 American Institute of Physics.
    No preview · Article · Feb 1998 · Applied Physics Letters
  • C. A. Wang · H. K. Choi · D. C. Oakley · G. W. Charache
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    ABSTRACT: The effect of substrate misorientation on the growth of GaInAsSb was studied for epilayers grown lattice-matched to GaSb substrates by low-pressure organometallic vapor phase epitaxy. The substrates were (100) misoriented 2 or 6° toward (110), (111)A, or (111)B. The surface is mirror-like and featureless for layers grown with a 6° toward (111)B misorientation, while, a slight texture was observed for layers grown on all other misorientations. The optical quality of layers, as determined by the full width at half-maximum of photoluminescence spectra measured at 4K, is significantly better for layers grown on substrates with a 6° toward (111)B misorientation. The incorporation of Zn as a p-type dopant in GaInAsSb is about 1.5 times more efficient on substrates with 6° toward (111)B misorientation compared to 2° toward (110) misorientation. The external quantum efficiency of thermophotovoltaic devices is not, however, significantly affected by substrate misorientation.
    No preview · Article · Jan 1998 · MRS Online Proceeding Library
  • C. A. Wang · H. K. Choi · D. C. Oakley · G. W. Charache
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    ABSTRACT: Studies on the materials development of Ga1−xInxAsySb1−y alloys for thermophotovoltaic (TPV) devices are reported. Ga1−xInxAsySb1−y epilayers were grown lattice-matched to GaSb substrates by organometallic vapor-phase epitaxy (OMVPE) using all organometallic precursors including triethylgallium, trimethylindium, tertiarybutylarsine, and trimethylantimony with diethyltellurium and dimethylzinc as the n- and p-type dopants, respectively. The epilayer characteristics of these alloys depend on growth temperature, In and As content, V/III ratio, and substrate misorientation. A mirror-like surface morphology and room-temperature photoluminescence (PL) are obtained for GaInAsSb layers with peak emission in the wavelength range between 2 and 2.5μm. The material properties of the metastable alloys improve for growth temperature decreasing from 575°C to 525°C and with decreasing In and As content, as based on epilayer surface morphology, X-ray diffraction, and low-temperature PL spectra. In general, GaInAsSb layers grown on (100)GaSb substrates with a 6° toward (111)B misorientation exhibit overall better material quality than layers grown on the more standard substrate (100) 2° toward (110). Consistent growth of high-performance lattice-matched GaInAsSb TPV devices is also demonstrated.
    No preview · Article · Jan 1998