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Articles 1 - 23 of 23
Full-Text Articles in Physics
Ga-Doped Zno Films Grown On Gan Templates By Plasma-Assisted Molecular-Beam Epitaxy, H. J. Ko, Yanfang Chen, S. K. Hong, H. Wenisch, T. Yao, David C. Look
Ga-Doped Zno Films Grown On Gan Templates By Plasma-Assisted Molecular-Beam Epitaxy, H. J. Ko, Yanfang Chen, S. K. Hong, H. Wenisch, T. Yao, David C. Look
Physics Faculty Publications
We have investigated the structural and optical properties of Ga-doped ZnO films grown on GaN templates by plasma-assisted molecular-beam epitaxy. The carrier concentration in Ga-doped ZnO films can be controlled from 1.33×1018/cm3 to 1.13×1020/cm3. Despite high Ga incorporation, the linewidth of (0002) ω-rocking curves of Ga-doped ZnO films still lies in the range from 5 to 15 arc min. Photoluminescence (PL) spectra of Ga-doped ZnO films show dominant near-bandedge emission with negligibly weak deep-level emission, independent of carrier concentration. The PL spectrum exhibits a new emission line at 3.358 eV, which corresponds to …
Combined Effects Of Screening And Band Gap Renormalization On The Energy Of Optical Transitions In Zno And Gan, D. C. Reynolds, David C. Look, B. Jogai
Combined Effects Of Screening And Band Gap Renormalization On The Energy Of Optical Transitions In Zno And Gan, D. C. Reynolds, David C. Look, B. Jogai
Physics Faculty Publications
The energy positions of the optical transitions in both GaN and ZnO were investigated when the samples were excited simultaneously with a HeCd laser and an Ar+ ion laser. The increased number of free electrons excited by the Ar+ ion laser will effectively screen both the free exciton and bound exciton transitions, resulting in a blueshift. The increased number of free electrons also produces many-body effects, which lead to a reduction of the band gap energy and thus a redshift. The resultant of screening and renormalization results in a redshift of the optical transitions in ZnO but a …
Paramagnetic Meissner Effect In Nb Disks, Petru S. Fodor, Lowell E. Wenger
Paramagnetic Meissner Effect In Nb Disks, Petru S. Fodor, Lowell E. Wenger
Physics Faculty Publications
Further details of the zero-field-cooled-magnetization and field-cooled-magnetization results on Nb disks exhibiting the paramagnetic Meissner effect (PME) are described. These studies indicate that two well-defined temperatures can be associated with features in the magnetization results. The higher characteristic temperature Tu is correlated with appearance of the paramagnetic moment and is strongly dependent upon the process used in forming the disk-shaped geometry of these Nb samples. The lower temperature Tp is associated with the “intrinsic coupling” of the interior Nb platelets. These latest results are shown to be consistent with the flux compression model for the appearance of the PME.
Electron Beam And Optical Depth Profiling Of Quasibulk Gan, L. Chernyak, A. Osinsky, G. Nootz, A. Schulte, J. Jasinski, M. Benamara, Z. Liliental-Weber, David C. Look, Richard J. Molnar
Electron Beam And Optical Depth Profiling Of Quasibulk Gan, L. Chernyak, A. Osinsky, G. Nootz, A. Schulte, J. Jasinski, M. Benamara, Z. Liliental-Weber, David C. Look, Richard J. Molnar
Physics Faculty Publications
Electron beam and optical depth profiling of thick (5.5–64 μm) quasibulk n-type GaN samples, grown by hydride vapor-phase epitaxy, were carried out using electron beam induced current (EBIC), microphotoluminescence (PL), and transmission electron microscopy (TEM). The minority carrier diffusion length, L, was found to increase linearly from 0.25 μm, at a distance of about 5 μm from the GaN/sapphire interface, to 0.63 μm at the GaN surface, for a 36-μm-thick sample. The increase in L was accompanied by a corresponding increase in PL band-to-band radiative transition intensity as a function of distance from the GaN/sapphire interface. We attribute …
Identification Of The Gamma(5) And Gamma(6) Free Excitons In Gan, D. C. Reynolds, David C. Look, B. Jogai, A. W. Saxler, Seong-Ju S. Park, J. Y. Hahn
Identification Of The Gamma(5) And Gamma(6) Free Excitons In Gan, D. C. Reynolds, David C. Look, B. Jogai, A. W. Saxler, Seong-Ju S. Park, J. Y. Hahn
Physics Faculty Publications
The Γ5 and Γ6 free excitons have been identified in GaN from emission measurements. Another emission peak is also observed which we believe to be the longitudinal free exciton. These measurements along with electrical measurements, which show the sample to have very high peak mobility, attest to the high quality of the sample.
Exterior Caustics Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder: Semiclassical Scattering Theory Analysis, James A. Lock, Charles L. Adler, Edward A. Hovenac
Exterior Caustics Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder: Semiclassical Scattering Theory Analysis, James A. Lock, Charles L. Adler, Edward A. Hovenac
Physics Faculty Publications
Rie use the semiclassical limit of electromagnetic wave scattering theory to determine the properties of the exterior caustics of a diagonally incident plane wave scattered by an infinitely long homogeneous dielectric circular cylinder in both the near zone and the far zone. The transmission caustic has an exterior/interior cusp transition as the tilt angle of the incident beam is increased, and each of the rainbow caustics has a far-zone rainbow/exterior cusp transition and an exterior/interior cusp transition as the incident beam tilt angle is increased. We experimentally observe and analyze both transitions of the first-order rainbow. We also compare the …
Supernumerary Spacing Of Rainbows Produced By An Elliptical-Cross-Section Cylinder. I. Theory, James A. Lock
Supernumerary Spacing Of Rainbows Produced By An Elliptical-Cross-Section Cylinder. I. Theory, James A. Lock
Physics Faculty Publications
A sequence of rainbows is produced in light scattering by a particle of high symmetry in the short-wavelength Limit, and a supernumerary interference pattern occurs to one side of each rainbow. Using both a ray-tracing procedure and the Debye-series decomposition of first-order perturbation wave theory, I examine the spacing of the supernumerary maxima and minima as a function of the cylinder rotation angle when an elliptical-cross-section cylinder is normally illuminated by a plane wave. I find that the supernumerary spacing depends sensitively on the cylinder-cross-section shape, and the spacing varies sinusoidally as a function of the cylinder rotation angle for …
Photoluminescence Measurements From The Two Polar Faces Of Zno, R. E. Sherriff, D. C. Reynolds, David C. Look, B. Jogai, J. E. Hoelscher, T. C. Collins, G. Cantwell, W. C. Harsch
Photoluminescence Measurements From The Two Polar Faces Of Zno, R. E. Sherriff, D. C. Reynolds, David C. Look, B. Jogai, J. E. Hoelscher, T. C. Collins, G. Cantwell, W. C. Harsch
Physics Faculty Publications
The crystal structure of ZnO is wurtzite and the stacking sequence of atomic layers along the “c” axis is not symmetric. As a result, a ZnO crystal surface that is normal to the c axis exposes one of two distinct polar faces, with (0001̄) being considered the O face and (0001) the Zn face. Photoluminescence (PL) measurements on the two faces reveal a striking difference. Two transitions are observed in PL that are dominant from the O face and barely observed in PL from the Zn face. These lines are identified as phonon replicas of a particular D …
Two-Level Atom In An Optical Parametric Oscillator: Spectra Of Transmitted And Fluorescent Fields In The Weak Driving Field Limit, James P. Clemens, Perry R. Rice, Pranaw Kumar Rungta, Robert J. Brecha
Two-Level Atom In An Optical Parametric Oscillator: Spectra Of Transmitted And Fluorescent Fields In The Weak Driving Field Limit, James P. Clemens, Perry R. Rice, Pranaw Kumar Rungta, Robert J. Brecha
Physics Faculty Publications
We consider the interaction of a two-level atom inside an optical parametric oscillator. In the weak-driving-field limit, we essentially have an atom-cavity system driven by the occasional pair of correlated photons, or weakly squeezed light. We find that we may have holes, or dips, in the spectrum of the fluorescent and transmitted light. This occurs even in the strong-coupling limit when we find holes in the vacuum-Rabi doublet. Also, spectra with a subnatural linewidth may occur. These effects disappear for larger driving fields, unlike the spectral narrowing obtained in resonance fluorescence in a squeezed vacuum; here it is important that …
Properties Of Semi‐Insulating Gaas:Fe Grown By Hydride Vapor Phase Epitaxy, E. Rodríguez Messmer, D. Söderström, P. Hult, S. Marcinkevicius, S. Lourdudoss, David C. Look
Properties Of Semi‐Insulating Gaas:Fe Grown By Hydride Vapor Phase Epitaxy, E. Rodríguez Messmer, D. Söderström, P. Hult, S. Marcinkevicius, S. Lourdudoss, David C. Look
Physics Faculty Publications
In this paper we analyze GaAs grown by hydride vapor phase epitaxy (HVPE) and doped with four different iron concentrations between and . From temperature dependent current‐voltage measurements we observed the highest resistivity in the lowest doped sample. We also quantified the activation energy. These results together with those of time resolved photoluminescence measurements indicate that in the sample with the lowest Fe concentration, EL2 may be dominant. From the analysis of the time resolved photoluminescence measurements, the intrinsic EL2 concentration and the electron and hole capture cross sections of Fe in GaAs were estimated. © 2000 The Electrochemical Society. …
Strain Variation With Sample Thickness In Gan Grown By Hydride Vapor Phase Epitaxy, D. C. Reynolds, David C. Look, B. Jogai, J. E. Hoelscher, R. E. Sherriff, Richard J. Molnar
Strain Variation With Sample Thickness In Gan Grown By Hydride Vapor Phase Epitaxy, D. C. Reynolds, David C. Look, B. Jogai, J. E. Hoelscher, R. E. Sherriff, Richard J. Molnar
Physics Faculty Publications
High quality GaN crystals can be grown on sapphire by hydride vapor phase epitaxy. The thermal expansion mismatch between sapphire and GaN produces strain in the GaN crystal as it is cooled from the growth temperature to room temperature. The strain is evidenced by shifts in the photoluminescence and reflectance line positions. By analyzing the surface strain as the crystal thickness is increased, the thickness required to obtain zero surface strain can be estimated. This structure might provide a lattice matched and thermally matched substrate for further epitaxial growth of GaN.
Time-Resolved Photoluminescence Lifetime Measurements Of The Gamma(5) And Gamma(6) Free Excitons In Zno, D. C. Reynolds, David C. Look, B. Jogai, J. E. Hoelscher, R. E. Sherriff, M. T. Harris, M. J. Callahan
Time-Resolved Photoluminescence Lifetime Measurements Of The Gamma(5) And Gamma(6) Free Excitons In Zno, D. C. Reynolds, David C. Look, B. Jogai, J. E. Hoelscher, R. E. Sherriff, M. T. Harris, M. J. Callahan
Physics Faculty Publications
Time-resolved photoluminescence spectroscopy at 2 K was used to measure the radiative recombination lifetime of the allowed (Γ5) and forbidden (Γ6) free excitons in ZnO. The measurements were made on a sample containing internal strain, which altered the sample symmetry, and resulted in relaxed selection rules, allowing the Γ6 exciton to be observed. A radiative recombination lifetime of 259 ps was measured for the Γ5 exciton and 245 ps for the Γ6 exciton. The decay of the free excitons was of single-exponential form, and the decay times were obtained using a least-squares fit …
Electrical Properties Of Boron-Doped P-Sigec Grown On N(-)-Si Substrate, M. Ahoujja, Y. K. Yeo, R. L. Hengehold, G. S. Pomrenke, David C. Look, J. Huffman
Electrical Properties Of Boron-Doped P-Sigec Grown On N(-)-Si Substrate, M. Ahoujja, Y. K. Yeo, R. L. Hengehold, G. S. Pomrenke, David C. Look, J. Huffman
Physics Faculty Publications
Electrical properties of fully strained boron-doped Si0.90−yGe0.10Cy/n−–Si grown by low pressure chemical vapor deposition have been investigated as a function of carbon content (0.2%–1.5%), using the variable temperature (25–650 K) Hall-effect technique. The results of Hall-effect measurements show that the Si substrate and the SiGeC/Si interfacial layer affect significantly the electrical properties of the SiGeC epitaxial layer. Thus, a three-layer conducting model has been used to extract the carrier concentration and mobility of the SiGeC layer alone. At room temperature, the hole carrier concentration decreases from 6.8×1017 to 2.4×10 …
Molecular-Dynamics Study Of Phase Transitions In Alkali Thiocyanates, M. M. Ossowski, John R. Hardy, Robert W. Smith
Molecular-Dynamics Study Of Phase Transitions In Alkali Thiocyanates, M. M. Ossowski, John R. Hardy, Robert W. Smith
Physics Faculty Publications
An account is presented of our studies of the order-disorder phase transitions in KSCN, RbSCN, and CsSCN. These are based on parameter-free interionic potentials based on the Gordon-Kim modified electron gas formalism extended to molecular ions. We performed static structural relaxations and supercell molecular dynamics and predicted with reasonable accuracy the temperatures for the onset of the transitions. In particular, we address the question of how the SCN2 ions disorder to yield subsequent structural transformations. We found high-temperature phases of average Fm3¯m symmetry for both KSCN and RbSCN. We argue that in reality the full appearance of these phases is …
Comment On “Direct Observation Of Stretched-Exponential Relaxation In Low-Temperature Lennard-Jones Systems Using The Cage Correlation Function”, Ulrich Zürcher, T. Keyes
Comment On “Direct Observation Of Stretched-Exponential Relaxation In Low-Temperature Lennard-Jones Systems Using The Cage Correlation Function”, Ulrich Zürcher, T. Keyes
Physics Faculty Publications
A Comment on the Letter by Eran Rabani, J. Daniel Gezelter, and D. J. Berne, Phys. Rev. Lett. 82, 3649 (1999). The authors of the Letter offer a Reply.
Dissociation Of Al2o3(0001) Substrates And The Roles Of Silicon And Oxygen In N-Type Gan Thin Solid Films Grown By Gas-Source Molecular Beam Epitaxy, J. E. Van Nostrand, J. Solomon, A. Saxler, Q. H. Xie, D. C. Reynolds, David C. Look
Dissociation Of Al2o3(0001) Substrates And The Roles Of Silicon And Oxygen In N-Type Gan Thin Solid Films Grown By Gas-Source Molecular Beam Epitaxy, J. E. Van Nostrand, J. Solomon, A. Saxler, Q. H. Xie, D. C. Reynolds, David C. Look
Physics Faculty Publications
Unintentionally doped and silicon doped GaN films prepared by molecular beam epitaxy using ammonia are investigated. Hall, secondary ion mass spectroscopy (SIMS), photoluminescence, and x-ray data are utilized for analysis of sources of autodoping of GaN epitaxial films in an effort to identify whether the n-type background electron concentration is of impurity origin or native defect origin. We identify and quantify an anomalous relationship between the Si doping concentration and free carrier concentration and mobility using temperature dependent Hall measurements on a series of 2.0-μm-thick GaN(0001) films grown on sapphire with various Si doping concentrations. SIMS is used to …
Zno Diode Fabricated By Excimer-Laser Doping, Toru Aoki, Yoshinori Hatanaka, David C. Look
Zno Diode Fabricated By Excimer-Laser Doping, Toru Aoki, Yoshinori Hatanaka, David C. Look
Physics Faculty Publications
A ZnO diode was fabricated by using a laser-doping technique to form a p-type ZnO layer on an n-type ZnO substrate. A zinc-phosphide compound, used as a phosphorous source, was deposited on the ZnO wafer and subjected to excimer-laser pulses. The current–voltage characteristics showed a diode characteristic between the phosphorous-doped p-layer and the n-type substrate. Moreover, light emission, with a band-edge component, was observed by forward current injection at 110 K.
On The Main Irradiation-Induced Defect In Gan, L. Polenta, Z-Q. Fang, David C. Look
On The Main Irradiation-Induced Defect In Gan, L. Polenta, Z-Q. Fang, David C. Look
Physics Faculty Publications
We show that the usual Arrhenius analysis of the main electron-irradiation-induced defect trap in n-type GaN, observed by deep-level transient spectroscopy (DLTS), is not sufficiently accurate. Instead, an exact fitting of the DLTS spectrum for this trap reveals two components, each of which has a thermal energy near 60 meV, not the apparent 140–200 meV, as given in other DLTS studies. This result resolves the discrepancy between Hall-effect and DLTS determinations of the thermal energy of this defect center.
Causal Implications Of Viscous Damping In Compressible Fluid Flows, P. M. Jordan, Martin R. Meyer, Ashok Puri
Causal Implications Of Viscous Damping In Compressible Fluid Flows, P. M. Jordan, Martin R. Meyer, Ashok Puri
Physics Faculty Publications
Classically, a compressible, isothermal, viscous fluid is regarded as a mathematical continuum and its motion is governed by the linearized continuity, Navier-Stokes, and state equations. Unfortunately, solutions of this system are of a diffusive nature and hence do not satisfy causality. However, in the case of a half-space of fluid set to motion by a harmonically vibrating plate the classical equation of motion can, under suitable conditions, be approximated by the damped wave equation. Since this equation is hyperbolic, the resulting solutions satisfy causal requirements. In this work the Laplace transform and other analytical and numerical tools are used to …
Quantitative Analysis Of Ultra-Fine Goethite In Rust Layer On Steel Using Mossbauer And X-Ray Diffraction Spectroscopy, Masato Yamashita, Toshihei Misawa, H. E. Townsend, D. C. Cook
Quantitative Analysis Of Ultra-Fine Goethite In Rust Layer On Steel Using Mossbauer And X-Ray Diffraction Spectroscopy, Masato Yamashita, Toshihei Misawa, H. E. Townsend, D. C. Cook
Physics Faculty Publications
We have proposed determination procedure of the relative amounts of rust constituents of steel. Mossbauer spectroscopy provides the relative amounts of crystalline rust constituents including ultra-fine crystals. A quantitative analysis of ultra-fine crystals is possible with the resolution of several percent by comparing the Mossbauer results with the relative amounts of rust constituents determined by X-ray diffraction spectroscopy.
Renormalons As Dilation Modes In The Functional Space, A. Babansky, I. Balitsky
Renormalons As Dilation Modes In The Functional Space, A. Babansky, I. Balitsky
Physics Faculty Publications
There are two possible sources of the factorial large-order behavior of a typical perturbative series. First, the number of different Feynman diagrams may be large; second, there may be abnormally large diagrams known as renormalons. It is well known that the large combinatorial number of diagrams is described by instanton-type solutions of the classical equations. We demonstrate that, from the functional-integral viewpoint, the renormalons do not correspond to a particular configuration but manifest themselves as dilatation modes in the functional space.
High Energy Effective Action From Scattering Of Shock Waves In Qcd, Ian Balitsky
High Energy Effective Action From Scattering Of Shock Waves In Qcd, Ian Balitsky
Physics Faculty Publications
The author demonstrates that the amplitude for high-energy scattering can be factorized as a convolution of the contributions due to fast and slow fields. The fast and slow fields interact by means of Wilson-line operators -- infinite gauge factors ordered along the straight line. The resulting factorization formula gives a starting point for a new approach to the effective action for high-energy scattering in QCD.
Deeply Virtual Compton Scattering At Small X, Ian Balitsky, Elena Kuchina
Deeply Virtual Compton Scattering At Small X, Ian Balitsky, Elena Kuchina
Physics Faculty Publications
We calculate the cross section of deeply virtual Compton scattering at large energies and intermediate momentum transfers.