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Full-Text Articles in Physics

Interaction Of A Group Of Dislocations Within The Framework Of The Continuum Frenkel-Kontorova Model, Naum I. Gershenzon Nov 1994

Interaction Of A Group Of Dislocations Within The Framework Of The Continuum Frenkel-Kontorova Model, Naum I. Gershenzon

Physics Faculty Publications

The Frenkel-Kontorova (FK) model of edge dislocation is analyzed. Solutions of the continuum limit of the FK model [the sine-Gordon (SG) equation] are obtained in a form convenient for investigation of dynamics of a large number of interacting dislocations. We consider, based on these solutions, some nonstationary processes: dislocation generation, diffusion of dislocations, and crack-dislocation interaction. Simple relations connecting the velocity of plastic deformation, density and velocity of dislocations, and the force of interaction between dislocations are obtained. The nucleation of dislocations at a moving crack tip is described.


Magnetoluminescence Studies In Gaas-Alxga1-Xas Single Heterojunctions - Observation Of Parity-Forbidden Landau-Level Transitions, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz, R. Jones, K. K. Bajaj Oct 1994

Magnetoluminescence Studies In Gaas-Alxga1-Xas Single Heterojunctions - Observation Of Parity-Forbidden Landau-Level Transitions, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz, R. Jones, K. K. Bajaj

Physics Faculty Publications

We have observed a number of allowed and parity-forbidden Landau-level transitions in a modulation-doped GaAs-AlxGa1-xAs single heterojunction structure using photoluminescence-excitation spectroscopy at 2 K. The GaAs layer in this structure is 5000 Å thick. From the allowed Landau-level transitions we determine the reduced mass of the electron-hole pair to be 0.07me. Using a heavy-hole mass of 0.45me, we determine the average value of the electron effective mass to be 0.084me. From the parity-forbidden transitions where the hole Landau level is the same but the electron Landau levels are different, we ...


Nondestructive Mapping Of Carrier Concentration And Dislocation Density In N(+)-Type Gaas, David C. Look, D. C. Walters, M. G. Mier, J. R. Sizelove Oct 1994

Nondestructive Mapping Of Carrier Concentration And Dislocation Density In N(+)-Type Gaas, David C. Look, D. C. Walters, M. G. Mier, J. R. Sizelove

Physics Faculty Publications

Transmission mappings (500 μm×500 μm resolution) at wavelengths of 0.9–1.5 μm on 3 in., n+‐GaAs wafers (n≂1–2×1018 cm-3) correlate well with carrier concentration n, measured by the Hall effect, and dislocation density, as confirmed by KOH etch‐pit patterns. The absorption for λ≳1.0 μm (below band edge) varies directly with n via free‐carrier interconduction‐band transitions, while the absorption for λ≲0.95 μm (near band edge) varies inversely with n because of band‐filling effects. Both phenomena are highly useful for n+‐GaAs wafer characterization.


Diamagnetic Shifts Of Excitons Associated With Symmetrical And Antisymmetric Wave Functions In Coupled Inxga1-Xas-Gaas Quantum Wells, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz Oct 1994

Diamagnetic Shifts Of Excitons Associated With Symmetrical And Antisymmetric Wave Functions In Coupled Inxga1-Xas-Gaas Quantum Wells, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz

Physics Faculty Publications

Magneto‐optical data obtained from photoluminescence and photoluminescence excitation measurements performed in the presence of applied magnetic fields were used to determine the diamagnetic shifts of free excitons. The samples studied were coupled InxGa1−xAs–GaAs quantum wells. In all cases the excitons associated with antisymmetric wave functions were found to have larger diamagnetic shifts than the excitons associated with symmetric wave functions. This suggests that the excitons associated with antisymmetric wave functions have a smaller binding energy than excitons associated with symmetric wave functions. These properties are consistent with the fact that excitons associated with ...


Radiative Recombination At The Alxga1-Xas-Gaas Heterostructure Interface By 2-Dimensional Excitons, D. C. Reynolds, David C. Look, B. Jogai, Phil W. Yu, K. Evans, C. E. Stutz, L. Radomsky Sep 1994

Radiative Recombination At The Alxga1-Xas-Gaas Heterostructure Interface By 2-Dimensional Excitons, D. C. Reynolds, David C. Look, B. Jogai, Phil W. Yu, K. Evans, C. E. Stutz, L. Radomsky

Physics Faculty Publications

Radiative recombination from the AlxGa1-xAs-GaAs heterostructure interface was investigated using photoluminescence and photoluminescence-excitation spectroscopy in modulation-doped and undoped samples. This emission is identified as H-band A, resulting from an indirect excitonlike transition in real space. The exciton is made up of a two-dimensional electron in the interface notch and a valence-band hole in the neutral region, having a binding energy of 1.8 meV. The H-band A exciton is directly excited by a free exciton making a vertical transition in real space. H-band A may be a distortion of the vertical direct free exciton in real ...


Deep Traps In Molecular-Beam-Epitaxial Gaas Grown At Low Temperatures, David C. Look, Z-Q. Fang, H. Yamamoto, J. R. Sizelove, M. G. Mier, C. E. Stutz Jul 1994

Deep Traps In Molecular-Beam-Epitaxial Gaas Grown At Low Temperatures, David C. Look, Z-Q. Fang, H. Yamamoto, J. R. Sizelove, M. G. Mier, C. E. Stutz

Physics Faculty Publications

Deep‐level transient spectroscopy has been performed on Si‐doped GaAs layers grown by molecular‐beam epitaxy at substrate temperatures of 400–450 °C. The λ effect is taken into account and overlapping peaks are analyzed numerically. An 0.65 eV electron trap of concentration 2×1016 cm−3 is believed to be related to the AsGa‐associated 0.65 eV Hall‐effect center, and also to the trap EB4 found in electron‐irradiated GaAs.


Magneto-Hall Characterization Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Structures, David C. Look, B. Jogai, C. E. Stutz, R. E. Sherriff, G. C. Desalvo, T. J. Rogers, J. M. Ballingall Jul 1994

Magneto-Hall Characterization Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Structures, David C. Look, B. Jogai, C. E. Stutz, R. E. Sherriff, G. C. Desalvo, T. J. Rogers, J. M. Ballingall

Physics Faculty Publications

Conventional Hall‐effect determination of the two‐dimensional electron gas (2DEG) concentration n2D in pseudomorphic high electron mobility transistor structures is invalid because of interference from the highly doped GaAs cap. Furthermore, the usual methods of dealing with this cap‐interference problem, namely, (1) etching off the cap totally, (2) etching the cap until the mobility reaches a maximum, or (3) growing a separate structure with a thin, depleted cap, in general, give n2D values that are too low. However, we show here that magnetic‐field‐dependent Hall (M‐Hall) measurements can separately determine the carrier concentrations and ...


Observation Of A Metastable Defect Transition In Gaas, David C. Look, Z-Q. Fang, J. R. Sizelove Jun 1994

Observation Of A Metastable Defect Transition In Gaas, David C. Look, Z-Q. Fang, J. R. Sizelove

Physics Faculty Publications

We show that the well-known 0.15-eV donor in bulk GaAs quenches under IR-light illumination and that the quenched (metastable) state has an electronic transition energy about 0.14 eV deeper than the ground state and can be observed by temperature-dependent-resistivity and Hall-effect measurements. The quenched state thermally recovers by an Auger-like process at a rate of r=2.3×10-12 nvn exp(-0.18/kT). Many of the properties exhibited by this donor are similar to those predicted theoretically for the complex defect AsGa-VAs.


Electrochemical Capacitance-Voltage Analysis Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Material, C. E. Stutz, B. Jogai, David C. Look, J. M. Ballingall, T. J. Rogers May 1994

Electrochemical Capacitance-Voltage Analysis Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Material, C. E. Stutz, B. Jogai, David C. Look, J. M. Ballingall, T. J. Rogers

Physics Faculty Publications

This work shows how electrochemical capacitance‐voltage (ECV) measurements can be used to evaluate delta‐doped pseudomorphic high electron mobility transistor material. These ECV measurements are compared with magnetic‐field‐dependent Hall effect (M‐Hall) measurements and a self‐consistent Poisson/kp calculation of the band structure and electron concentration. The ECV technique can clearly delineate the cap layer, the delta‐doped layer, and the InxGa1−xAs channel layer, whereas the M‐Hall method characterizes only the cap and InxGa1−xAs channel layers. The amount of electron charge ...


Low-Temperature Growth Of High Resistivity Gaas By Photoassisted Metalorganic Chemical Vapor Deposition, J. C. Roberts, K. S. Boutros, S. M. Bedair, David C. Look May 1994

Low-Temperature Growth Of High Resistivity Gaas By Photoassisted Metalorganic Chemical Vapor Deposition, J. C. Roberts, K. S. Boutros, S. M. Bedair, David C. Look

Physics Faculty Publications

We report the photoassisted low‐temperature (LT) metalorganic chemical vapor deposition (MOCVD) of high resistivity GaAs. The undoped as‐grown GaAs exhibits a resistivity of ∼106 Ω cm, which is the highest reported for undoped material grown in the MOCVD environment. Photoassisted growth of doped and undoped device quality GaAs has been achieved at a substrate temperature of 400 °C in a modified atmospheric pressure MOCVD reactor. By using silane as a dopant gas, the LT photoassisted doped films have high levels of doping and electron mobilities comparable to those achieved by MOCVD for growth temperatures, Tg≳600 ...


Observation Of Free And Bound Excitons Associated With The 2-Dimensional Electron-Gas In Modulation-Doped Heterostructures, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz Apr 1994

Observation Of Free And Bound Excitons Associated With The 2-Dimensional Electron-Gas In Modulation-Doped Heterostructures, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz

Physics Faculty Publications

Overlapping bulk and two-dimensional excitons have been observed in modulation-doped heterostructures. Their differing behavior in a magnetic field allows them to be studied separately. Both free and bound excitons, associated with the two-dimensional electron gas, have been observed in the photoluminescence spectra of these structures. These excitons show a reduced binding energy due to screening and are found in a region of the structure where band-gap renormalization occurs due to many-body interactions. The two-dimensional excitons are identified from measurements conducted in applied magnetic fields.


Rate Coefficient For The Reaction N + No, Jane L. Fox Jan 1994

Rate Coefficient For The Reaction N + No, Jane L. Fox

Physics Faculty Publications

Evidence has been advanced that the rate coefficient for the reaction N + NO → N2; + O has a small positive temperature dependence at the high temperatures (900-1500 K) that prevail in the terrestrial middle and upper thermosphere by Siskind and Rusch (1992), and at the low temperatures (100-200 K) of the Martian lower thermosphere by Fox (1993). Assuming that the rate coefficient recommended by the Jet Propulsion Laboratory evaluation (DeMore et al., 1992) is accurate at 300 K, we derive here the low temperature value of the activation energy for this reaction and thus the rate coefficient that best fits ...


Hopping Conduction In Molecular Beam Epitaxial Gaas Grown At Very Low Temperatures, David C. Look, Z-Q. Fang, J. W. Look, J. R. Sizelove Jan 1994

Hopping Conduction In Molecular Beam Epitaxial Gaas Grown At Very Low Temperatures, David C. Look, Z-Q. Fang, J. W. Look, J. R. Sizelove

Physics Faculty Publications

Conductivity and Hall effect measurements have been performed on 2 μm thick molecular beam epitaxial layers grown at very low substrate temperatures, 200 to 400°C. For growth temperatures below 300°C, the conduction is dominated by hopping between arsenic antisite defects of concentrations up to 1020 cm−3. Below measurement temperatures of about 130 K, the hopping conduction can be quenched by strong IR light illumination, because the antisite then becomes metastable. The antisite has a thermal activation energy of , and thus is not identical to the famous EL2. Both nearest‐neighbor and variable‐range hopping mechanisms are ...