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Full-Text Articles in Physics

Introduction And Recovery Of Ga And N Sublattice Defects In Electron-Irradiated Gan, F. Tuomisto, V. Ranki, David C. Look, Gary C. Farlow Oct 2007

Introduction And Recovery Of Ga And N Sublattice Defects In Electron-Irradiated Gan, F. Tuomisto, V. Ranki, David C. Look, Gary C. Farlow

Physics Faculty Publications

We have used positron annihilation spectroscopy to study the introduction and recovery of point defects introduced by 0.45 and 2 MeV electron irradiation at room temperature in n-type GaN. Isochronal annealings were performed up to 1220 K. We observe vacancy defects with specific lifetime of τV=190±15 ps that we tentatively identify as N vacancies or related complexes in the neutral charge state in the samples irradiated with 0.45 MeV electrons. The N vacancies are produced at a rate ΣN0.45≃0.25 cm−1. The irradiation with 2 MeV electrons produces negatively charged ...


Near-Terminator Venus Ionosphere: How Chapman-Esque?, Jane L. Fox Sep 2007

Near-Terminator Venus Ionosphere: How Chapman-Esque?, Jane L. Fox

Physics Faculty Publications

We have modeled the near-terminator ionosphere of Venus for solar zenith angles χ between 60 and 85° in 5° increments, and from 86 to 90° in 1° increments. The most important neutral densities of the background thermospheres have been adopted from the VTS3 model of Hedin et al. (1983), which is based on densities from the Pioneer Venus (PV) Orbiter Neutral Mass Spectrometer (e.g., Niemann et al., 1980) that are normalized to the PV Orbiter Atmospheric Drag data (e.g., Keating et al., 1980). We compare the ion density profiles to those of a Chapman layer and to those ...


Near-Terminator Venus Ionosphere: Evidence For A Dawn/Dusk Asymmetry In The Thermosphere, Jane L. Fox, W. T. Kasprzak Sep 2007

Near-Terminator Venus Ionosphere: Evidence For A Dawn/Dusk Asymmetry In The Thermosphere, Jane L. Fox, W. T. Kasprzak

Physics Faculty Publications

Recent models of the near-terminator ionosphere of Venus constructed using neutral density profiles from the VTS3 model of Hedin et al. (1983) have shown that altitudes of the electron density peaks are in agreement with those measured by Pioneer Venus (PV) Orbiter Radio Occultation (ORO) and other radio occultation profiles in the solar zenith angle (SZA) range 60 to 70°, where they are near 140 km (Fox, 2007). The model peaks in the 75–85° range, however, do not decrease in altitude to near 135 km, as do the PV ORO electron density peaks shown in the study of Cravens ...


Thermally Driven Defect Formation And Blocking Layers At Metal-Zno Interfaces, H. L. Mosbacker, C. Zgrabik, M. J. Hetzer, A. Swain, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson Aug 2007

Thermally Driven Defect Formation And Blocking Layers At Metal-Zno Interfaces, H. L. Mosbacker, C. Zgrabik, M. J. Hetzer, A. Swain, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson

Physics Faculty Publications

The authors used depth-resolved cathodoluminescence spectroscopy and current-voltage measurements to probe the temperature-dependent formation of native point defects and reaction layers at metal-ZnO interfaces and their effect on transport properties. These results identify characteristic defect emissions corresponding to metal-Zn alloy versus oxide formation. Au alloys with Zn above its eutectic temperature, while Ta forms oxide blocking layers that reduce current by orders of magnitude at intermediate temperatures. Defects generated at higher temperatures and/or with higher initial defect densities for all interfaces produce Ohmic contacts. These reactions and defect formation with annealing reveal a thermodynamic control of blocking versus Ohmic ...


Electron And Hole Traps In N-Doped Zno Grown On P-Type Si By Metalorganic Chemical Vapor Deposition, Z-Q. Fang, B. Claflin, David C. Look, Lei L. Kerr, Xiaonan Li Jul 2007

Electron And Hole Traps In N-Doped Zno Grown On P-Type Si By Metalorganic Chemical Vapor Deposition, Z-Q. Fang, B. Claflin, David C. Look, Lei L. Kerr, Xiaonan Li

Physics Faculty Publications

Electron and hole traps in N-doped ZnO were investigated using a structure of n+-ZnO:Al/i-ZnO/ZnO:N grown on a p-Si substrate by metalorganic chemical vapor deposition (for growth of the ZnO:N layer) and sputtering deposition (for growth of the i-ZnO and n+-ZnO:Al layers). Current-voltage and capacitance-voltage characteristics measured at temperatures from 200 to 400 K show that the structure is an abrupt n+p diode with very low leakage currents. By using deep level transient spectroscopy, two hole traps, H3 (0.35 eV) and H4 (0.48 eV), are found in ...


Role Of Subsurface Defects In Metal-Zno(0001) Schottky Barrier Formation, H. L. Mosbacker, S. El Hage, M. Gonzalez, S. A. Ringel, M. J. Hetzer, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson Jul 2007

Role Of Subsurface Defects In Metal-Zno(0001) Schottky Barrier Formation, H. L. Mosbacker, S. El Hage, M. Gonzalez, S. A. Ringel, M. J. Hetzer, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson

Physics Faculty Publications

The authors fabricated diodes of Au, Al, Ni, Pt, Pd, Mo, Ta, and Ir on single crystal ZnO(0001) surfaces from different vendors and measured their Schottky barriers, idealities, and reverse currents on as-received and remote oxygen (20% O2/80%He) plasma-treated surfaces. Using low temperature nanoscale depth-resolved cathodoluminescence spectroscopy (DRCLS) under the metal, the authors identified the presence of defect transitions at 2.1, 2.5, and 3.0 eV that change dramatically depending on the process steps and choice of metal. I-V measurements exhibited transitions from Ohmic to Schottky and lower idealities for Pt, Au, Ir, and ...


Electron Irradiation Induced Deep Centers In Hydrothermally Grown Zno, Z-Q. Fang, B. Claflin, David C. Look, Gary C. Farlow Apr 2007

Electron Irradiation Induced Deep Centers In Hydrothermally Grown Zno, Z-Q. Fang, B. Claflin, David C. Look, Gary C. Farlow

Physics Faculty Publications

An n-type hydrothermally grown ZnO sample becomes semi-insulating (ρ~108 Ω cm) after 1-MeV electron-irradiation. Deep traps produced by the irradiation were studied by thermally stimulated current spectroscopy. The dominant trap in the as-grown sample has an activation energy of 0.24 eV and is possibly related to LiZn acceptors. However, the electron irradiation introduces a new trap with an activation energy of 0.15 eV, and other traps of energy 0.30 and 0.80 eV, respectively. From a comparison of these results with positron annihilation experiments and density functional theory, we conclude that the 0 ...


Dominant Effect Of Near-Interface Native Point Defects On Zno Schottky Barriers, L. J. Brillson, H. L. Mosbacker, M. J. Hetzer, Y. Strzhemechny, David C. Look, G. Cantwell, J. Zhang, J. J. Song Mar 2007

Dominant Effect Of Near-Interface Native Point Defects On Zno Schottky Barriers, L. J. Brillson, H. L. Mosbacker, M. J. Hetzer, Y. Strzhemechny, David C. Look, G. Cantwell, J. Zhang, J. J. Song

Physics Faculty Publications

The authors used depth-resolved cathodoluminescence spectroscopy and current-voltage measurements to probe metal-ZnO diodes as a function of native defect concentration, oxygen plasma processing, and metallization. The results show that resident native defects in ZnO single crystals and native defects created by the metallization process dominate metal-ZnO Schottky barrier heights and ideality factors. Results for ZnO(0001) faces processed with room temperature remote oxygen plasmas to remove surface adsorbates and reduce subsurface native defects demonstrate the pivotal importance of crystal growth quality and metal-ZnO reactivity in forming near-interface states that control Schottky barrier properties.


The Effect Of Si Doping On The Electrical Properties Of B12as2 Thin Films On (0001) 6h-Sic Substrates, Zhou Xu, J. H. Edgar, David C. Look, S. Baumann, R. J. Bleiler, S. H. Wang, S. E. Mohney Mar 2007

The Effect Of Si Doping On The Electrical Properties Of B12as2 Thin Films On (0001) 6h-Sic Substrates, Zhou Xu, J. H. Edgar, David C. Look, S. Baumann, R. J. Bleiler, S. H. Wang, S. E. Mohney

Physics Faculty Publications

The ability to control the resistivity of the wide band gap semiconductor B12As2 by doping with silicon was verified. The electrical properties of nominally undoped and Si-doped rhombohedral B12As2 thin films on semi-insulating 6H-SiC (0001) substrates prepared by chemical vapor deposition were subjected to Hall effect measurements. Varying the Si concentration in the B12As2 thin films from 7×1018 to 7×1021 at./cm3 (as measured by secondary ion mass spectrometry) decreased the resistivities of the p-type B12As2 films from 2×10 ...


The Metal-Insulator Transition In Vo2 Studied Using Terahertz Apertureless Near-Field Microscopy, Hui Zhan, Victoria Astley, Michael Hvasta, Jason A. Deibel, Daniel M. Mittleman, Yong-Sik Lim Jan 2007

The Metal-Insulator Transition In Vo2 Studied Using Terahertz Apertureless Near-Field Microscopy, Hui Zhan, Victoria Astley, Michael Hvasta, Jason A. Deibel, Daniel M. Mittleman, Yong-Sik Lim

Physics Faculty Publications

We have studied the metal-insulator transition in a vanadium dioxide (VO2) thin film using terahertz apertureless near-field optical microscopy. We observe a variation of the terahertz amplitude due to the phase transition induced by an applied voltage across the sample. The change of the terahertz signal is related to the abrupt change of the conductivity of the VO2 film at the metal-insulator transition. The subwavelength spatial resolution of this near-field microscopy makes it possible to detect signatures of micron-scale metallic domains in inhomogeneous VO2 thin films.


Temperature Dependence Of Terahertz Emission From Inmnas, Hui Zhan, Jason A. Deibel, Jonathan Laib, Chanjuan Sun, Junichiro Kono, Daniel M. Mittleman, Hiro Munekata Jan 2007

Temperature Dependence Of Terahertz Emission From Inmnas, Hui Zhan, Jason A. Deibel, Jonathan Laib, Chanjuan Sun, Junichiro Kono, Daniel M. Mittleman, Hiro Munekata

Physics Faculty Publications

No abstract provided.


Students’ Use Of Symmetry With Gauss’S Law, Adrienne L. Traxler, Katrina E. Black, John R. Thompson Jan 2007

Students’ Use Of Symmetry With Gauss’S Law, Adrienne L. Traxler, Katrina E. Black, John R. Thompson

Physics Faculty Publications

To study introductory student difficulties with electrostatics, we compared student techniques when finding the electric field for spherically symmetric and non-spherically symmetric charged conductors. We used short interviews to design a free-response and multiple-choice-multiple-response survey that was administered to students in introductory calculus-based courses. We present the survey results and discuss them in light of Singh's results for Gauss's Law, Collins and Ferguson's epistemic forms and games, and Tuminaro's extension of games and frames.


Electron And Hole Traps In N-Doped Zno Grown On P-Type Si Substrate By Mocvd, Zhaoqiang Fang, Bruce B. Claflin, David C. Look, Lei L. Kerr, Xiaonan Li Jan 2007

Electron And Hole Traps In N-Doped Zno Grown On P-Type Si Substrate By Mocvd, Zhaoqiang Fang, Bruce B. Claflin, David C. Look, Lei L. Kerr, Xiaonan Li

Physics Faculty Publications

Electron and hole traps in N-doped ZnO were investigated using a structure of n+-ZnO:Al/i-ZnO/ZnO:N grown on a p-Si substrate by metalorganic chemical vapor deposition (for growth of the ZnO:N layer) and sputtering deposition (for growth of the i-ZnO and n+-ZnO:Al layers). Current-voltage and capacitance-voltage characteristics measured at temperatures from 200 to 400 K show that the structure is an abrupt n+p diode with very low leakage currents. By using deep level transient spectroscopy, two hole traps, H3 (0.35 eV) and H4 (0.48 eV), are found in ...