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Articles 1 - 11 of 11
Full-Text Articles in Physical Sciences and Mathematics
Comparisons Of Electron Fluxes Measured In The Crustal Fields At Mars By The Mgs Magnetometer/Electron Reflectometer Instrument With A B Field-Dependent Transport Code, Michael W. Liemohn, David L. Mitchell, Andrew F. Nagy, Jane L. Fox, Tamara W. Reimer, Yingjuan J. Ma
Comparisons Of Electron Fluxes Measured In The Crustal Fields At Mars By The Mgs Magnetometer/Electron Reflectometer Instrument With A B Field-Dependent Transport Code, Michael W. Liemohn, David L. Mitchell, Andrew F. Nagy, Jane L. Fox, Tamara W. Reimer, Yingjuan J. Ma
Physics Faculty Publications
We compare Mars Global Surveyor (MGS) magnetometer/electron reflectometer data with results from a B field–dependent kinetic transport code for ‘‘superthermal’’ electrons. The photoelectrons created on crustal field loops, when they are on the dayside, allow for the exploration of the magnetic topology and the upper atmospheric density structure. A case study of a typical orbit of the MGS satellite through the strong crustal field region in the southern hemisphere of Mars is examined. The results indicate that the low solar wind dynamic pressure during the selected orbit allowed for the expansion of the crustal field line to relatively high altitudes. …
Fabrication And Characterization Of N-Zno/P-Algan Heterojunction Light-Emitting Diodes On 6h-Sic Substrates, Ya I. Alivov, E. V. Kalinina, A. E. Cherenkov, David C. Look, B. M. Ataev, A. K. Omaev, M. V. Chukichev, D. M. Bagnall
Fabrication And Characterization Of N-Zno/P-Algan Heterojunction Light-Emitting Diodes On 6h-Sic Substrates, Ya I. Alivov, E. V. Kalinina, A. E. Cherenkov, David C. Look, B. M. Ataev, A. K. Omaev, M. V. Chukichev, D. M. Bagnall
Physics Faculty Publications
We report on the fabrication of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates. Hydride vapor phase epitaxy was used to grow p-type AlGaN, while chemical vapor deposition was used to produce the n-type ZnO layers. Diode-like, rectifying I-V characteristics, with threshold voltage ~3.2 V and low reverse leakage current ~10-7 A, are observed at room temperature. Intense ultraviolet emission with a peak wavelength near 389 nm is observed when the diode is forward biased; this emission is found to be stable at temperatures up to 500 K and shown to originate from recombination within the ZnO.
Evidence Of The Zn Vacancy Acting As The Dominant Acceptor In N-Type Zno, F. Tuomisto, V. Ranki, K. Saarinen, David C. Look
Evidence Of The Zn Vacancy Acting As The Dominant Acceptor In N-Type Zno, F. Tuomisto, V. Ranki, K. Saarinen, David C. Look
Physics Faculty Publications
We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (Eel=2 MeV, fluence 6×1017 cm-2) ZnO samples. The Zn vacancies are identified at concentrations of [VZn]≃2×1015 cm-3 in the as-grown material and [VZn]≃2×1016 cm-3 in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.
Observation Of 430 Nm Electroluminescence From Zno/Gan Heterojunction Light-Emitting Diodes, Ya I. Alivov, J. E. Van Nostrand, David C. Look, M. V. Chukichev, B. M. Ataev
Observation Of 430 Nm Electroluminescence From Zno/Gan Heterojunction Light-Emitting Diodes, Ya I. Alivov, J. E. Van Nostrand, David C. Look, M. V. Chukichev, B. M. Ataev
Physics Faculty Publications
In this work, we report on the growth, fabrication, and device characterization of wide-band-gap heterojunction light-emitting diodes based on the n-ZnO/p-GaN material system. The layer structure is achieved by first growing a Mg-doped GaN film of thickness 1 μm on Al2O3(0001) by molecular-beam epitaxy, then by growing Ga-doped ZnO film of thickness 1 μm by chemical vapor deposition on the p-GaN layer. Room-temperature electroluminescence in the blue-violet region with peak wavelength 430 nm is observed from this structure under forward bias. Light–current characteristics of these light-emitting diodes are reported, and a superlinear …
Remote Hydrogen Plasma Processing Of Zno Single Crystal Surfaces, Yuri M. Strzhemechny, John Nemergut, Phillip E. Smith, Junjik Bae, David C. Look, Leonard J. Brillson
Remote Hydrogen Plasma Processing Of Zno Single Crystal Surfaces, Yuri M. Strzhemechny, John Nemergut, Phillip E. Smith, Junjik Bae, David C. Look, Leonard J. Brillson
Physics Faculty Publications
We have studied the effects of remote hydrogen plasma treatment on the defect characteristics in single crystal ZnO. Temperature-dependent (9–300 K) and excitation intensity-dependent photoluminescence spectra reveal that H-plasma exposure of ZnO effectively suppresses the free-exciton transition and redistributes intensities in the bound-exciton line set and two-electron satellites with their phonon replicas. The resultant spectra after hydrogenation exhibit a relative increase in intensity of the I4 (3.363 eV) peak, thought to be related to a neutral donor bound exciton, and a peak feature at 3.366 eV with a distinctly small thermal activation energy. Hydrogenation also produces a violet 100 …
On The Nitrogen Vacancy In Gan, David C. Look, Gary C. Farlow, P. J. Drevinsky, D. F. Bliss, J. R. Sizelove
On The Nitrogen Vacancy In Gan, David C. Look, Gary C. Farlow, P. J. Drevinsky, D. F. Bliss, J. R. Sizelove
Physics Faculty Publications
The dominant electrically active defect produced by 0.42 MeV electron irradiation in GaN is a 70 meV donor. Since only N-sublattice displacements can be produced at this energy, and since theory predicts that the N interstitial is a deep acceptor in n-type GaN, we argue that the 70 meV donor is most likely the isolated N vacancy. The background shallow donors, in the 24–26 meV range, actually decrease in concentration, probably due to interactions with mobile N interstitials that are produced by the irradiation. Thus, the recent assignment of a photoluminescence (PL) line as an exciton bound to a …
Frequency Scanned Interferometer Demonstration System, Tim Blass, Jason A. Deibel, Sven Nyberg, Keith Riles, Haijun Yang
Frequency Scanned Interferometer Demonstration System, Tim Blass, Jason A. Deibel, Sven Nyberg, Keith Riles, Haijun Yang
Physics Faculty Publications
No abstract provided.
Effect Of H-2 On The Martian Ionosphere: Implications For Atmospheric Evolution, Jane L. Fox
Effect Of H-2 On The Martian Ionosphere: Implications For Atmospheric Evolution, Jane L. Fox
Physics Faculty Publications
Because H2 reacts efficiently with O+, CO2 +, CO+, and N2 +, the molecular hydrogen abundance assumed in models of the Martian ionosphere greatly affects the high altitude density profiles of these ions. We have found that models of the low solar activity Martian ionosphere exhibit much smaller O+ densities than the measured values if the adopted H2 abundance is of the order of 40 ppm, the value proposed in a 1998 model of the Martian atmosphere. For a model based on the recently measured H2 abundance of …
Ga Vacancies As Dominant Intrinsic Acceptors In Gan Grown By Hydride Vapor Phase Epitaxy, J. Oila, J. Kivioja, V. Ranki, K. Saarinen, David C. Look, Richard J. Molnar, S. S. Park, S. K. Lee, J. Y. Han
Ga Vacancies As Dominant Intrinsic Acceptors In Gan Grown By Hydride Vapor Phase Epitaxy, J. Oila, J. Kivioja, V. Ranki, K. Saarinen, David C. Look, Richard J. Molnar, S. S. Park, S. K. Lee, J. Y. Han
Physics Faculty Publications
Positron annihilation measurements show that negative Ga vacancies are the dominant acceptors in n-type gallium nitride grown by hydride vapor phase epitaxy. The concentration of Ga vacancies decreases, from more than 1019 to below 1016 cm−3, as the distance from the interface region increases from 1 to 300 μm. These concentrations are the same as the total acceptor densities determined in Hall experiments. The depth profile of O is similar to that of VGa, suggesting that the Ga vacancies are complexed with the oxygen impurities.
Plasma-Etching-Enhanced Deep Centers In N-Gan Grown By Metalorganic Chemical-Vapor Deposition, Z-Q. Fang, David C. Look, X. L. Wang, J. Han, F. A. Khan, I. Adesida
Plasma-Etching-Enhanced Deep Centers In N-Gan Grown By Metalorganic Chemical-Vapor Deposition, Z-Q. Fang, David C. Look, X. L. Wang, J. Han, F. A. Khan, I. Adesida
Physics Faculty Publications
By using deep-level transient spectroscopy (DLTS), deep centers have been characterized in unintentionally doped n-GaN samples grown by metalorganic chemical-vapor deposition and subjected to inductively coupled plasma reactive ion etching. At least six DLTS traps exist in the control sample: A1 (∼0.90 eV), Ax (∼0.72 eV), B (0.61 eV), C1 (0.44 eV), D (0.25 eV), and E1 (0.17 eV), with B dominant. Then, as the etching bias-voltage increases from −50 to −150 V, trap D increases strongly and becomes dominant, while traps A1, C (0.34 eV), and E1 increase at a slower …
Hydrogen Incorporation And Diffusivity In Plasma-Exposed Bulk Zno, K. Ip, M. E. Overberg, Y. W. Heo, D. P. Norton, S. J. Pearton, C. E. Stutz, B. Luo, F. Ren, David C. Look, J. M. Zavada
Hydrogen Incorporation And Diffusivity In Plasma-Exposed Bulk Zno, K. Ip, M. E. Overberg, Y. W. Heo, D. P. Norton, S. J. Pearton, C. E. Stutz, B. Luo, F. Ren, David C. Look, J. M. Zavada
Physics Faculty Publications
Hydrogen incorporation depths of >25 μm were obtained in bulk, single-crystal ZnO during exposure to 2H plasmas for 0.5 h at 300 °C, producing an estimated diffusivity of ∼ 8×10−10 cm2/V⋅s at this temperature. The activation energy for diffusion was 0.17±0.12 eV, indicating an interstitial mechanism. Subsequent annealing at 500–600 °C was sufficient to evolve all of the hydrogen out of the ZnO, at least to the sensitivity of secondary ion mass spectrometry (<5×1015 cm−3). The thermal stability of hydrogen retention is slightly greater when the hydrogen is incorporated by direct implantation …