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Full-Text Articles in Physics

Fabrication And Characterization Of N-Zno/P-Algan Heterojunction Light-Emitting Diodes On 6h-Sic Substrates, Y. I. Alivov, E. V. Kalinina, A. E. Cherenkov, David C. Look, B. M. Ataev, A. K. Omaev, M. V. Chukichev, D. M. Bagnall Dec 2003

Fabrication And Characterization Of N-Zno/P-Algan Heterojunction Light-Emitting Diodes On 6h-Sic Substrates, Y. 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.


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 Dec 2003

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 ...


Evidence Of The Zn Vacancy Acting As The Dominant Acceptor In N-Type Zno, F. Tuomisto, V. Ranki, K. Saarinen, David C. Look Nov 2003

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.


On The Nitrogen Vacancy In Gan, David C. Look, Gary C. Farlow, P. J. Drevinsky, D. F. Bliss, J. R. Sizelove Oct 2003

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 ...


Observation Of 430 Nm Electroluminescence From Zno/Gan Heterojunction Light-Emitting Diodes, Y. I. Alivov, J. E. Van Nostrand, David C. Look, M. V. Chukichev, B. M. Ataev Oct 2003

Observation Of 430 Nm Electroluminescence From Zno/Gan Heterojunction Light-Emitting Diodes, Y. 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 ...


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 Oct 2003

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 ...


Frequency Scanned Interferometer Demonstration System, Tim Blass, Jason A. Deibel, Sven Nyberg, Keith Riles, Haijun Yang Jul 2003

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 Jun 2003

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 15 ppm [ Krasnopolsky and Feldman, 2001a , 2001b], the O ...


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 May 2003

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 Mar 2003

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 ...


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 Jan 2003

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 ...