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Full-Text Articles in Physics
Unpinning Of Gaas Surface Fermi Level By 200 Degrees C Molecular Beam Epitaxial Layer, David C. Look, C. E. Stutz, K. R. Evans
Unpinning Of Gaas Surface Fermi Level By 200 Degrees C Molecular Beam Epitaxial Layer, David C. Look, C. E. Stutz, K. R. Evans
Physics Faculty Publications
Previous attempts to passivate the n‐type (100)GaAs surface have significantly reduced only the surface recombination centers, but not the surface acceptors which pin the Fermi level. Here we show that a 100 Å molecular beam epitaxial layer grown at 200 °C reduces the effective surface potential energy − eϕs from 0.70 to 0.17 eV, nearly eliminates light sensitivity, and permits nonalloyed ohmic contacts. After a 10 min, 450 °C anneal, − eϕs increases only to 0.22 eV.
Nonalloyed Ohmic Contacts On Low-Temperature Molecular-Beam Epitaxial Gaas: Influence Of Deep Donor Band, H. Yamamoto, Z-Q. Fang, David C. Look
Nonalloyed Ohmic Contacts On Low-Temperature Molecular-Beam Epitaxial Gaas: Influence Of Deep Donor Band, H. Yamamoto, Z-Q. Fang, David C. Look
Physics Faculty Publications
The Ohmic nature of the nonalloyed metal contact on molecular beam epitaxial GaAs grown at 200 °C was studied. The specific contact resistances at room temperature and 120 K were 1.5×10−3 and 7.0×10−1 Ω cm2, respectively. These values are anomalously low considering that the conduction‐band electron concentration in this material is less than 1011 cm−3 at room temperature. The experimental results indicate that the carrier transport at the metal/semiconductor interface is dominated by a dense (∼3×1019 cm−3) EL2‐like deep donor band, rather than the usual conduction band.
Anomalous Hall-Effect Results In Low-Temperature Molecular-Beam-Epitaxial Gaas - Hopping In A Dense El2-Like Band, David C. Look, D. C. Walters, M. O. Manasreh, J. R. Sizelove, C. E. Stutz, K. R. Evans
Anomalous Hall-Effect Results In Low-Temperature Molecular-Beam-Epitaxial Gaas - Hopping In A Dense El2-Like Band, David C. Look, D. C. Walters, M. O. Manasreh, J. R. Sizelove, C. E. Stutz, K. R. Evans
Physics Faculty Publications
Molecular-beam-epitaxial GaAs grown at very low temperatures (∼200 °C) exhibits anomalous Hall-effect properties. Here we show conclusively that the room-temperature conduction is due to activated (nearest-neighbor) hopping in a deep defect band of concentration 3×1019 cm-3, and energy Ec-0.75 eV, along with conduction due to free carriers thermally excited from this band. At low measurement temperatures, variable-range hopping [σ∝exp(-T0/T)1/4] prevails. The conduction-band mobility can be well explained by neutral-deep-donor scattering in parallel with lattice scattering.
Infrared-Absorption Of Deep Defects In Molecular-Beam-Epitaxial Gaas-Layers Grown At 200°C - Observation Of An El(2)-Like Defect, M. O. Manasreh, David C. Look, K. R. Evans
Infrared-Absorption Of Deep Defects In Molecular-Beam-Epitaxial Gaas-Layers Grown At 200°C - Observation Of An El(2)-Like Defect, M. O. Manasreh, David C. Look, K. R. Evans
Physics Faculty Publications
Infrared optical absorption and Hall-effect techniques were employed to study deep defects in As-rich molecular-beam-epitaxial GaAs layers grown at very low temperature (200°C). A large ir absorption band was observed between 0.55 eV and the band edge. This band is composed of photoquenchable and photounquenchable components. Photoquenching, thermal recovery from the metastable state, and ir absorption properties of the quenchable defect, of estimated concentration ~3x1018 cm-3, are identical to those of EL2. On the other hand, the unquenchable defect, of estimated concentration ~3x1019 cm-3, resembles the isolated AsGa, antisite observed in …
Surface And Interface Free-Carrier Depletion In Gaas Molecular Beam Epitaxial Layers: Demonstration Of High Interface Charge, David C. Look, C. E. Stutz, K. R. Evans
Surface And Interface Free-Carrier Depletion In Gaas Molecular Beam Epitaxial Layers: Demonstration Of High Interface Charge, David C. Look, C. E. Stutz, K. R. Evans
Physics Faculty Publications
Molecular beam epitaxial GaAs layers of electron concentration 1.69×1017 cm−3, and various thicknesses d=0.25, 0.50, 1.00, and 2.00 μm, have been grown on semi‐insulating GaAs substrates and characterized by the Hall effect and capacitance‐voltage (C‐V) techniques. A plot of sheet Hall concentration ns vs d gives accurate values of (ND−NA) and (ws+wi), the sum of the surface and interface free‐carrier depletion widths, respectively. The C‐V measurements verify the value of ND−NA …
Surface And Interface Free-Carrier Depletion In Gaas Molecular-Beam Epitaxial Layers: Demonstration Of High Interface Charge, David C. Look, C. E. Stutz, K. R. Evans
Surface And Interface Free-Carrier Depletion In Gaas Molecular-Beam Epitaxial Layers: Demonstration Of High Interface Charge, David C. Look, C. E. Stutz, K. R. Evans
Physics Faculty Publications
Molecular beam epitaxial GaAs layers of electron concentration 1.69×1017 cm−3, and various thicknesses d=0.25, 0.50, 1.00, and 2.00 μm, have been grown on semi‐insulating GaAs substrates and characterized by the Hall effect and capacitance‐voltage (C‐V) techniques. A plot of sheet Hall concentration ns vs d gives accurate values of (ND−NA) and (ws+wi), the sum of the surface and interface free‐carrier depletion widths, respectively. The C‐V measurements verify the value of ND−NA …
Theoretical Intensity-Dependent Response Of Nonlinear Periodic Structures, Paul A. Gohman, Gust Bambakidis, Robert J. Spry
Theoretical Intensity-Dependent Response Of Nonlinear Periodic Structures, Paul A. Gohman, Gust Bambakidis, Robert J. Spry
Physics Faculty Publications
We have modeled the response of a nonlinear periodic structure by means of the Abelés 2×2 matrix method. Our structure differs from the usual rejection‐band filter designs, in that we have chosen the filter elements to be index matched in the absence of radiation, providing a rejection band that both grows and shifts as a function of incident intensity. The intensity output function of the model not only directly demonstrates optical bistability, but also limiting, switching, self‐pulsing, and chaos.
In Situ Hall-Effect System For Real-Time Electron-Irradiation Studies, B. S. Ziebro, David C. Look, Joseph W. Hemsky, J. Rice
In Situ Hall-Effect System For Real-Time Electron-Irradiation Studies, B. S. Ziebro, David C. Look, Joseph W. Hemsky, J. Rice
Physics Faculty Publications
A unique system capable of taking in situ Hall‐effect measurements during electron irradiation has been developed. The key element is a small, powerful rare‐earth magnet. Measurements can be taken while the electron beam is on, resulting in a considerable time savings and eliminating problems associated with mounting and demounting the sample. High resolution electron concentration and mobility versus fluence data are quickly and easily obtained, making possible detailed defect production rate studies as functions of energy and flux.
Review Of Hall Effect And Magnetoresistance Measurements In Gaas Materials And Devices, David C. Look
Review Of Hall Effect And Magnetoresistance Measurements In Gaas Materials And Devices, David C. Look
Physics Faculty Publications
The use of magnetic fields in the electrical characterization of semiconductor materials is familiar to everyone in the form of Hall‐effect measurements. However, there is another magnetic‐field‐based phenomenon, magnetoresistance (MR), which is highly useful but not nearly so familiar to the majority of workers. One of the unique features of MR measurements is their applicability to common device structures, in particular, field‐effect transistors (FETs) and contact‐resistance patterns. We will show how channel mobility information can be extracted from the MR data in metal‐semiconductor FETs (MESFETs) and modulation‐doped heterostructure FETs (MODFETs), and also how the material under ohmic contacts can be …
Transition Probabilities And Franck-Condon Factors For The Second Negative Band System Of O2+, Jane L. Fox, Alexander Dalgarno
Transition Probabilities And Franck-Condon Factors For The Second Negative Band System Of O2+, Jane L. Fox, Alexander Dalgarno
Physics Faculty Publications
Transition probabilities for the second negative band system of O2+ are computed using the dipole transition moment presented by Wetmore et al. [1984]. Vibrational levels υ″ = 0 − 54 of the X²Πg ground state and υ′ = 0 − 33 of the excited A²Πu state are included. Franck-Condon factors for ionization-excitation of O2 (X³Σg−; υ = 0 − 25) to O2+(A²Πu;υ′ = 0 − 33) are also presented.
A Signature Of Auroral Precipitation In The Nightside Ionosphere Of Venus, Jane L. Fox, H. A. Taylor Jr.
A Signature Of Auroral Precipitation In The Nightside Ionosphere Of Venus, Jane L. Fox, H. A. Taylor Jr.
Physics Faculty Publications
We show here that the densities of mass-28 ions measured by the Pioneer Venus Orbiter ion mass spectrometer (OIMS) on the nightside of Venus are highly variable and show little correlation with the values of the O+ densities. We have determined the total production rates of mass-28 ions in the chemical equilibrium region and find that this production rate cannot be explained by known chemical production reactions. We propose that the “excess” production is due to precipitation of electrons into the nightside thermosphere.