George G. Bryant
Air Force Research Laboratory
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Featured researches published by George G. Bryant.
Journal of Crystal Growth | 2003
Joseph L. Morton; Nancy Ma; D. Bliss; George G. Bryant
During the liquid-encapsulated Czochralski (LEC) process, a single compound semiconductor crystal such as indium phosphide or gallium antimonide is grown by the solidification of an initially molten semiconductor contained in a crucible. The motion of the electrically conducting molten semiconductor can be controlled with an externally applied magnetic field. This paper presents a model for the unsteady transport of a dopant during the LEC process with a steady axial magnetic field. The convective species transport during growth produces significant segregation in both the melt and the crystal. Dopant distributions in the crystal and in the melt at several different stages during growth are presented.
Journal of Fluids Engineering-transactions of The Asme | 1998
Nancy Ma; John S. Walker; D. Bliss; George G. Bryant
This paper treats the forced convection, which is produced by the rotation of the crystal about its vertical centerline during the liquid-encapsulated Czochralski or Kyropoulos growth of compound semiconductor crystals, with a uniform vertical magnetic field. The model assumes that the magnetic field strength is sufficiently large that convective heat transfer and all inertial effects except the centripetal acceleration are negligible. With the liquid encapsulant in the radial gap between the outside surface of the crystal and the vertical wall of the crucible, the forced convection is fundamentally different from that with a free surface between the crystal and crucible for the Czochralski growth of silicon crystals. Again unlike the case for silicon growth, the forced convection for the actual nonzero electrical conductivity of an indium-phosphide crystal is virtually identical to that for an electrically insulating crystal. The electromagnetic damping of the forced convection is stronger than that of the buoyant convection. In order to maintain a given balance between the forced and buoyant convections, the angular velocity of the crystal must be increased as the magnetic field strength is increased.
Journal of Fluids Engineering-transactions of The Asme | 2001
Joseph L. Morton; Nancy Ma; D. Bliss; George G. Bryant
During the magnetically-stabilized liquid-encapsulated Czochralski (MLEC) process, a single compound semiconductor crystal is grown by the solidification of an initially molten semiconductor (melt) contained in a crucible. The melt is doped with an element in order to vary the electrical and/or optical properties of the crystal. During growth, the so-called melt-depletion flow caused by the opposing relative velocities of the encapsulant-melt interface and the crystal-melt interface can be controlled with an externally applied magnetic field. The convective dopant transport during growth driven by this melt motion produces nonuniformities of the dopant concentration in both the melt and the crystal. We present a model for the unsteady transport of a dopant during the MLEC process with an axial magnetic field. Dopant distributions in the crystal and in the melt at several different stages during growth are presented
SPIE's 1995 Symposium on OE/Aerospace Sensing and Dual Use Photonics | 1995
George G. Bryant; D. Bliss; David R. Gabbe; Franz X. Zach; Gerry W. Iseler
Twin-free single crystals of iron doped indium phosphide (InP:Fe) have been grown with different concentrations of iron dopants and shallow donor impurities using several techniques: magnetic liquid encapsulated Kyropoulos (MLEK), liquid encapsulated Czochralski (LEC), and vertical gradient freeze (VGF). Iron in InP falls into one of two defect states, and thus can be used as an infrared photorefractive (PR) material for amplifying coherent optical signals. The crystals above were compared in PR experiments at room temperature to measure two-wave mixing gain. The two defect states where then measured by independent means to determine a relationship between PR gain and defect concentration. From an analysis of these data the PR gain can be optimized by growing crystals under conditions which result in InP:Fe with an optimum Fe3+ concentration, optimum Fe3+/Fe2+ ratio, uniform dopant distribution, and low defect density.
Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest (2009), paper AWA1 | 2009
Candace Lynch; Vladimir Tassev; George G. Bryant; Cal Yapp; David F. Bliss
Millimeter-thick crystals of orientation-patterned GaAs have been grown using low pressure Hydride Vapor Phase Epitaxy for use in the generation of mid-IR and THz radiation.
Journal of Crystal Growth | 2001
W.M. Higgins; Gerald W. Iseler; D. Bliss; George G. Bryant; Vladimir Tassev; I Jafri; R.M. Ware; Douglas J. Carlson
High purity, stoichiometric InP is being produced in crucible-shaped, 3-kg charges by the phosphorus injection method in a high-pressure magnetic liquid encapsulated Czochralski (MLEC) crystal growth system. Dedicated heaters in the phosphorus injector assembly are used to heat and controllably inject the phosphorus vapor into the liquid encapsulated indium melt. Glow discharge mass spectroscopy and van der Pauw measurements of the polycrystalline charges and the Czochralski wafers confirmed the low background levels of impurities.
Journal of Crystal Growth | 2000
N Ma; D. Bliss; George G. Bryant
Abstract The dopant transport during growth depends on both the diffusion and the convection of dopant during the entire period of time needed to grow a crystal. The application of even a moderate magnetic field is enough to damp the melt motion in order to eliminate oscillatory or turbulent melt motions which cause microsegregation or striations, and provide the electromagnetic control needed to minimize macrosegregation. For the moderate-strength magnetic fields used during liquid-encapsulated crystal growth processes, the dopant transport in the melt is dominated by convection, and the constant-concentration curves resemble the streamlines. The strong flow adjacent to the crystal–melt interface produces a lateral uniformity in the dopant concentration in the melt adjacent to the interface and consequently in the crystal.
Journal of Crystal Growth | 2002
Joseph L. Morton; Nancy Ma; D. Bliss; George G. Bryant
Journal of Crystal Growth | 2012
Vladimir Tassev; Michael Snure; Rita D. Peterson; R. Bedford; D. Bliss; George G. Bryant; M. Mann; W. Goodhue; S. Vangala; Krongtip Termkoa; Angie Lin; James S. Harris; M. M. Fejer; C. Yapp; S. Tetlak
International Journal of Heat and Fluid Flow | 2007
Mei Yang; Nancy Ma; D. Bliss; George G. Bryant