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217 results on '"Wampler, W. R."'

2. Carrier capture and emission by substitutional carbon impurities in GaN vertical diodes.

Author

Wampler, W. R., Armstrong, A. M., and Vizkelethy, G.

Subjects
*CARBON emissions, *ELECTRON beams, *IONIZING radiation, *CHEMICAL vapor deposition, *DIODES, *ELECTRON sources
Abstract

A model was developed for the operation of a GaN pn junction vertical diode which includes rate equations for carrier capture and thermally activated emission by substitutional carbon impurities and carrier generation by ionizing radiation. The model was used to simulate the effect of ionizing radiation on the charge state of carbon. These simulations predict that with no applied bias, carbon is negatively charged in the n-doped layer, thereby compensating n-doping as experimentally observed in diodes grown by metal-organic chemical vapor deposition. With reverse bias, carbon remains negative in the depletion region, i.e., compensation persists in the absence of ionization but is neutralized by exposure to ionizing radiation. This increases charge density in the depletion region, decreases the depletion width, and increases the capacitance. The predicted increase in capacitance was experimentally observed using a pulsed 70 keV electron beam as the source of ionization. In additional confirming experiments, the carbon charge-state conversion was accomplished by photoionization using sub-bandgap light or by the capture of holes under forward bias. [ABSTRACT FROM AUTHOR]

Published
2022
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4. Net versus gross erosion of silicon carbide in DIII-D divertor

Author

Rudakov, D L, primary, Wampler, W R, additional, Abrams, T, additional, Ding, R, additional, Boedo, J A, additional, Bringuier, S, additional, Bykov, I, additional, Chrobak, C P, additional, Elder, J D, additional, Guo, H Y, additional, Lasnier, C J, additional, Mathison, E, additional, McLean, A G, additional, Sinclair, G, additional, Stangeby, P C, additional, Thomas, D M, additional, Unterberg, E A, additional, Wang, H, additional, and Watkins, J G, additional

Published
2020
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9. Field dependent emission rates in radiation damaged GaAs.

Author

Fleming, R. M., Myers, S. M., Wampler, W. R., Lang, D. V., Seager, C. H., and Campbell, J. M.

Subjects
TEMPERATURE, ELECTRIC fields, ELECTRONS, DOPED semiconductors, DIODES
Abstract

We have measured the temperature and field dependence of emission rates from five traps in electron damaged GaAs. Four of the traps have previously been identified as radiation defects. One of the traps, seen in higher doped diodes, has not been previously identified. We have fit the data to a multiphonon emission theory that allows recombination in GaAs to be characterized over a broad range of temperature and electric field. These results demonstrate an efficient method to calculate field-dependent emission rates in GaAs. [ABSTRACT FROM AUTHOR]

Published
2014
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14. Utilization of outer-midplane collector probes with isotopically enriched tungsten tracer particles for impurity transport studies in the scrape-off layer of DIII-D (invited)

Author

Donovan, D. C., primary, Unterberg, E. A., additional, Stangeby, P. C., additional, Zamperini, S., additional, Auxier, J. D., additional, Rudakov, D. L., additional, Wampler, W. R., additional, Zach, M., additional, Abrams, T., additional, Duran, J. D., additional, Elder, J. D., additional, and Neff, A. L., additional

Published
2018
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15. Model of defect reactions and the influence of clustering in pulse-neutron-irradiated Si.

Author

Myers, S. M., Cooper, P. J., and Wampler, W. R.

Subjects
CLUSTERING of particles, SILICON, NEUTRON irradiation, JUNCTION transistors, DIFFUSION, MATHEMATICAL continuum, POINT defects
Abstract

Transient reactions among irradiation defects, dopants, impurities, and carriers in pulse-neutron-irradiated Si were modeled taking into account the clustering of the primal defects in recoil cascades. Continuum equations describing the diffusion, field drift, and reactions of relevant species were numerically solved for a submicrometer spherical volume, within which the starting radial distributions of defects could be varied in accord with the degree of clustering. The radial profiles corresponding to neutron irradiation were chosen through pair-correlation-function analysis of vacancy and interstitial distributions obtained from the binary-collision code MARLOWE, using a spectrum of primary recoil energies computed for a fast-burst fission reactor. Model predictions of transient behavior were compared with a variety of experimental results from irradiated bulk Si, solar cells, and bipolar-junction transistors. The influence of defect clustering during neutron bombardment was further distinguished through contrast with electron irradiation, where the primal point defects are more uniformly dispersed. [ABSTRACT FROM AUTHOR]

Published
2008
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16. Lattice location of hydrogen in Mg doped GaN.

Author

Wampler, W. R., Myers, S. M., Wright, A. F., Barbour, J. C., Seager, C. H., and Han, J.

Subjects
*GALLIUM nitride, *DOPED semiconductors, *HYDROGEN content of metals
Abstract

We have used ion channeling to examine the lattice configuration of hydrogen in Mg doped wurtzite GaN grown by metal organic chemical vapor deposition. Hydrogen is introduced by exposure to hydrogen gas or electron cyclotron resonance plasmas and by ion implantation. A density functional approach including lattice relaxation was used to calculate total energies for various locations and charge states of hydrogen in the wurtzite Mg doped GaN lattice. Results of channeling measurements are compared with channeling simulations for hydrogen at lattice locations predicted by the density functional theory. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001
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17. Diffusion, release, and uptake of hydrogen in magnesium-doped gallium nitride: Theory and experiment.

Author

Myers, S. M., Wright, A. F., Petersen, G. A., Wampler, W. R., Seager, C. H., Crawford, M. H., and Han, J.

Subjects
HYDROGEN, GALLIUM nitride, DOPED semiconductors, DEUTERIUM, PERMEABILITY
Abstract

The diffusion and release of H and its uptake from the gas phase are modeled for Mg-doped, wurtzite GaN using formation energies and vibration frequencies from the density-function theory. Comparison is made with rates of deuterium release and uptake measured by nuclear-reaction analysis of deuterium concentration. Good agreement is found when account is taken of a surface permeation barrier. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001
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18. Equilibrium state of hydrogen in gallium nitride: Theory and experiment.

Author

Myers, S. M., Wright, A. F., Petersen, G. A., Seager, C. H., Wampler, W. R., Crawford, M. H., and Han Sandia, J.

Subjects
HYDROGEN, DENSITY functionals
Abstract

Calculates the formation energies and vibration frequencies of hydrogen in wurtzite GaN from density-functional theory. Prediction of equilibrium state occupancies and solid solubilities at elevated temperatures for p-type, intrinsic and n-type material; Measurement of the solubility of deuterium in p-type; Factors accounting for the equilibrium, elevated-temperature behavior of hydrogen.

Published
2000
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22. Tungsten erosion by unipolar arcing in DIII-D

Author

Bykov, I, primary, Chrobak, C P, additional, Abrams, T, additional, Rudakov, D L, additional, Unterberg, E A, additional, Wampler, W R, additional, Hollmann, E M, additional, Moyer, R A, additional, Boedo, J A, additional, Stahl, B, additional, Hinson, E T, additional, Yu, J H, additional, Lasnier, C J, additional, Makowski, M, additional, and McLean, A G, additional

Published
2017
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24. Influence of ambient on hydrogen release from p-type gallium nitride

Author

Myers, S. M., Vaandrager, B. L., Wampler, W. R., and Seager, C. H.

Subjects
Cyclotron resonance -- Research, Hydrogen -- Research, Hydrogen -- Electric properties, Gallium nitrate -- Research, Gallium nitrate -- Electric properties, Physics
Abstract

Mechanisms of H release from Mg-doped, p-type GaN is investigated in vacuum, in N2 and O2 gases, and in electron-cyclotron-resonance N2 plasmas. The results are quantitatively consistent with a theoretical model wherein the bulk solution is in equilibrium with surface states from which desorption occurs by processes that are both first and second order in surface coverage.

Published
2004

25. Surface-limited release of deuterium from tantalum.

Author

Wampler, W. R.

Subjects
*NUCLEAR reactions, *DEUTERIUM, *TANTALUM, *METALS, *SEMICONDUCTORS
Abstract

Focuses on a study which examined the release of deuterium (D) from solution in tantalum (Ta). Use of nuclear reaction analysis in the measurement; Details on the rate-controlling process for D release; Recombination coefficients for palladlium and Ta.

Published
1991
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26. Hydrogen permeation into iron.

Author

Wampler, W. R.

Subjects
*DEUTERIUM, *PERMEABILITY, *IRON, *ION bombardment
Abstract

Presents a study which measured the permeation of deuterium from the gas phase into solution in iron using a method based on ion beam analysis. Experimental method; Results; Discussion; Conclusions.

Published
1989
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27. Mechanism of surface-limited release of hydrogen from oxidized metals.

Author

Richards, P. M., Myers, S. M., Wampler, W. R., and Follstaedt, D. M.

Subjects
RECOMBINATION in semiconductors, DEUTERIUM, HELIUM, IRON
Abstract

Presents a study that analyzed the time dependence of surface recombination and release of deuterium from helium-bubble traps in iron with both clean and oxidized surfaces. Description of the second-order kinetics in both cases; Function of the oxides.

Published
1989
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28. Energy and density measurements of sloshing ions in tandem-mirror-experiment upgrade using solid-state probe techniques.

Author

Hsu, W. L., Bastasz, R., Wampler, W. R., Rensink, M. E., Allen, S. L., Grubb, D. P., and Simonen, T. C.

Subjects
IONS, MAGNETICS, MAGNETIC flux
Abstract

Presents a study that measured the energy and flux of charge-exchange neutrals from the sloshing ions in the endplug of tandem-mirror-experiment upgrade. Features of a tandem-mirror-experiment upgrade endplug; Methodology; Calculation of the sloshing ion distribution.

Published
1985
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30. Performance and Breakdown Characteristics of Irradiated Vertical Power GaN P-i-N Diodes

Author

King, M. P., primary, Armstrong, A. M., additional, Dickerson, J. R., additional, Vizkelethy, G., additional, Fleming, R. M., additional, Campbell, J., additional, Wampler, W. R., additional, Kizilyalli, I. C., additional, Bour, D. P., additional, Aktas, O., additional, Nie, H., additional, Disney, D., additional, Wierer, J., additional, Allerman, A. A., additional, Moseley, M. W., additional, Leonard, F., additional, Talin, A. A., additional, and Kaplar, R. J., additional

Published
2015
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32. Net versus gross erosion of high-Zmaterials in the divertor of DIII-D

Author

Rudakov, D L, primary, Stangeby, P C, additional, Wampler, W R, additional, Brooks, J N, additional, Brooks, N H, additional, Elder, J D, additional, Hassanein, A, additional, Leonard, A W, additional, McLean, A G, additional, Moyer, R A, additional, Sizyuk, T, additional, Watkins, J G, additional, and Wong, C P C, additional

Published
2014
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35. Plasma Surface Interaction (PSI) studies at DIII-D

Author

Wong, C. P. C., primary, Rudakov, D. L., additional, Brooks, J. N., additional, Brooks, N. H., additional, Buchenauer, D. A., additional, Chen, B., additional, Chrobak, C., additional, Doerner, R., additional, Elder, J. D., additional, Hassanein, A., additional, Hollmann, E. M., additional, Lasnier, C., additional, Leonard, T., additional, Litnovsky, A., additional, McLean, A. G., additional, Sizyuk, T., additional, Stangeby, P. C., additional, Tao, R., additional, Wall, D., additional, Wampler, W. R., additional, Watkins, J., additional, Wright, G., additional, Wright, M., additional, Luo, G. N., additional, and Zhong, G., additional

Published
2013
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36. C-13 transport studies in L-mode divertor plasmas on DIII-D

Author

Allen, S. L., Wampler, W. R., McLean, A. G., Whyte, D. G., West, W. P., Stangeby, P. C., Brooks, N. H., Rudakov, D. L., Phillips, V., Rubel, Marek J., Matthews, G. F., Nagy, A., Ellis, R., Bozek, A. S., Allen, S. L., Wampler, W. R., McLean, A. G., Whyte, D. G., West, W. P., Stangeby, P. C., Brooks, N. H., Rudakov, D. L., Phillips, V., Rubel, Marek J., Matthews, G. F., Nagy, A., Ellis, R., and Bozek, A. S.

Abstract

(CH4)-C-13 was injected with a toroidally-symmetric gas system into 22 identical lower-single-null L-mode discharges on DIII-D. The injection level was adjusted so that it did not significantly perturb the core or divertor plasmas, with a duration of similar to 3 s on each shot, for a total of similar to 300 T L of injected particles. The plasma shape remained very constant; the divertor strike points were controlled to similar to 1 cm at the divertor plate. At the beginning of the subsequent machine vent, 29 carbon tiles were removed for nuclear reaction analysis of C-13 content to determine regions of carbon deposition. It was found that only the tiles inboard of the inner strike point had appreciable 1 3 C above background. Visible spectroscopy measurements of the carbon injection and comparisons with modeling are consistent with carbon transport by means of scrape-off layer flow., QC 20100525 QC 20111012. 16th International Conference on Plasma Surface Interactions in Controlled Fusion Devices. Portland, ME. MAY 24-28, 2004

Published
2005
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38. Overview of the recent DiMES and MiMES experiments in DIII-D

Author

Rudakov, D L, primary, Wong, C P C, additional, Litnovsky, A, additional, Wampler, W R, additional, Boedo, J A, additional, Brooks, N H, additional, Fenstermacher, M E, additional, Groth, M, additional, Hollmann, E M, additional, Jacob, W, additional, Krasheninnikov, S I, additional, Krieger, K, additional, Lasnier, C J, additional, Leonard, A W, additional, McLean, A G, additional, Marot, M, additional, Moyer, R A, additional, Petrie, T W, additional, Philipps, V, additional, Smirnov, R D, additional, Stangeby, P C, additional, Watkins, J G, additional, West, W P, additional, and Yu, J H, additional

Published
2009
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41. The effect of lithium surface coatings on plasma performance in the National Spherical Torus Experiment

Author

Kugel, H. W., primary, Bell, M. G., additional, Ahn, J.-W., additional, Allain, J. P., additional, Bell, R., additional, Boedo, J., additional, Bush, C., additional, Gates, D., additional, Gray, T., additional, Kaye, S., additional, Kaita, R., additional, LeBlanc, B., additional, Maingi, R., additional, Majeski, R., additional, Mansfield, D., additional, Menard, J., additional, Mueller, D., additional, Ono, M., additional, Paul, S., additional, Raman, R., additional, Roquemore, A. L., additional, Ross, P. W., additional, Sabbagh, S., additional, Schneider, H., additional, Skinner, C. H., additional, Soukhanovskii, V., additional, Stevenson, T., additional, Timberlake, J., additional, Wampler, W. R., additional, and Zakharov, L., additional

Published
2008
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42. Scrape-off layer transport and deposition studies in DIII-D

Author

Groth, M., primary, Allen, S. L., additional, Boedo, J. A., additional, Brooks, N. H., additional, Elder, J. D., additional, Fenstermacher, M. E., additional, Groebner, R. J., additional, Lasnier, C. J., additional, McLean, A. G., additional, Leonard, A. W., additional, Lisgo, S., additional, Porter, G. D., additional, Rensink, M. E., additional, Rognlien, T. D., additional, Rudakov, D. L., additional, Stangeby, P. C., additional, Wampler, W. R., additional, Watkins, J. G., additional, West, W. P., additional, and Whyte, D. G., additional

Published
2007
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43. DiMES studies of temperature dependence of carbon erosion and re-deposition in the lower divertor of DIII-D under detachment

Author

Rudakov, D L, primary, Jacob, W, additional, Krieger, K, additional, Litnovsky, A, additional, Philipps, V, additional, West, W P, additional, Wong, C P C, additional, Allen, S L, additional, Bastasz, R J, additional, Boedo, J A, additional, Brooks, N H, additional, Boivin, R L, additional, Temmerman, G De, additional, Fenstermacher, M E, additional, Groth, M, additional, Hollmann, E M, additional, Lasnier, C J, additional, McLean, A G, additional, Moyer, R A, additional, Stangeby, P C, additional, Wampler, W R, additional, Watkins, J G, additional, Wienhold, P, additional, and Whaley, J, additional

Published
2007
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44. First tests of molybdenum mirrors for ITER diagnostics in DIII-D divertor

Author

Rudakov, D. L., primary, Boedo, J. A., additional, Moyer, R. A., additional, Litnovsky, A., additional, Philipps, V., additional, Wienhold, P., additional, Allen, S. L., additional, Fenstermacher, M. E., additional, Groth, M., additional, Lasnier, C. J., additional, Boivin, R. L., additional, Brooks, N. H., additional, Leonard, A. W., additional, West, W. P., additional, Wong, C. P. C., additional, McLean, A. G., additional, Stangeby, P. C., additional, De Temmerman, G., additional, Wampler, W. R., additional, and Watkins, J. G., additional

Published
2006
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46. Progress towards high-performance, steady-state spherical torus

Author

Ono, M, primary, Bell, M G, additional, Bell, R E, additional, Bigelow, T, additional, Bitter, M, additional, Blanchard, W, additional, Boedo, J, additional, Bourdelle, C, additional, Bush, C, additional, Choe, W, additional, Chrzanowski, J, additional, Darrow, D S, additional, Diem, S J, additional, Doerner, R, additional, Efthimion, P C, additional, Ferron, J R, additional, Fonck, R J, additional, Fredrickson, E D, additional, Garstka, G D, additional, Gates, D A, additional, Gray, T, additional, Grisham, L R, additional, Heidbrink, W, additional, Hill, K W, additional, Hoffman, D, additional, Jarboe, T R, additional, Johnson, D W, additional, Kaita, R, additional, Kaye, S M, additional, Kessel, C, additional, Kim, J H, additional, Kissick, M W, additional, Kubota, S, additional, Kugel, H W, additional, LeBlanc, B P, additional, Lee, K, additional, Lee, S G, additional, Lewicki, B T, additional, Luckhardt, S, additional, Maingi, R, additional, Majeski, R, additional, Manickam, J, additional, Maqueda, R, additional, Mau, T K, additional, Mazzucato, E, additional, Medley, S S, additional, Menard, J, additional, Mueller, D, additional, Nelson, B A, additional, Neumeyer, C, additional, Nishino, N, additional, Ostrander, C N, additional, Pacella, D, additional, Paoletti, F, additional, Park, H K, additional, Park, W, additional, Paul, S F, additional, Peng, Y-K M, additional, Phillips, C K, additional, Pinsker, R, additional, Probert, P H, additional, Ramakrishnan, S, additional, Raman, R, additional, Redi, M, additional, Roquemore, A L, additional, Rosenberg, A, additional, Ryan, P M, additional, Sabbagh, S A, additional, Schaffer, M, additional, Schooff, R J, additional, Seraydarian, R, additional, Skinner, C H, additional, Sontag, A C, additional, Soukhanovskii, V, additional, Spaleta, J, additional, Stevenson, T, additional, Stutman, D, additional, Swain, D W, additional, Synakowski, E, additional, Takase, Y, additional, Tang, X, additional, Taylor, G, additional, Timberlake, J, additional, Tritz, K L, additional, Unterberg, E A, additional, Halle, A Von, additional, Wilgen, J, additional, Williams, M, additional, Wilson, J R, additional, Xu, X, additional, Zweben, S J, additional, Akers, R, additional, Barry, R E, additional, Beiersdorfer, P, additional, Bialek, J M, additional, Blagojevic, B, additional, Bonoli, P T, additional, Carter, M D, additional, Davis, W, additional, Deng, B, additional, Dudek, L, additional, Egedal, J, additional, Ellis, R, additional, Finkenthal, M, additional, Foley, J, additional, Fredd, E, additional, Glasser, A, additional, Gibney, T, additional, Gilmore, M, additional, Goldston, R J, additional, Hatcher, R E, additional, Hawryluk, R J, additional, Houlberg, W, additional, Harvey, R, additional, Jardin, S C, additional, Hosea, J C, additional, Ji, H, additional, Kalish, M, additional, Lowrance, J, additional, Lao, L L, additional, Levinton, F M, additional, Luhmann, N C, additional, Marsala, R, additional, Mastravito, D, additional, Menon, M M, additional, Mitarai, O, additional, Nagata, M, additional, Oliaro, G, additional, Parsells, R, additional, Peebles, T, additional, Peneflor, B, additional, Piglowski, D, additional, Porter, G D, additional, Ram, A K, additional, Rensink, M, additional, Rewoldt, G, additional, Robinson, J, additional, Roney, P, additional, Shaing, K, additional, Shiraiwa, S, additional, Sichta, P, additional, Stotler, D, additional, Stratton, B C, additional, Vero, R, additional, Wampler, W R, additional, and Wurden, G A, additional

Published
2003
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