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  • 1
    Electronic Resource
    Electronic Resource
    Electron transverse energy distribution in GaAs negative electron affinity cathodes: Calculations compared to experiments (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1809-1815 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transverse momentum of photoelectrons released from a negative electron affinity GaAs cathode is small compared with other thermonic or field emission electron sources. A low photoelectron transverse momentum in vacuum promises highly focused, low-energy beams useful for numerous applications. A simplified theory for electron emission from GaAs predicts much lower electron transverse momentum than those previously measured experimentally. To address this theory–experiment mismatch, Monte Carlo based calculations were compared with experimental data. We checked the possibility of there being electron scattering in the Cs,O layer; however, none of the scattering checked (isotropically distributed, cosine distributed, and Rutherford scattering) properly fit the experimental results. The assumption of conservation of the parallel component of the crystal momentum k during the emission is mainly believed to be responsible for the calculation-theory disagreement. The best simulation-experiment fit was obtained through a relaxation of the conditions imposed on the transverse momentum inside and outside of the semiconductor when an ideal interface is considered. We obtained the best results by assuming that the effective mass of the electron inside GaAs is equal to the effective mass of the electron in vacuum. Two independent experiments confirmed that in both cases, this same-mass approximation gives the best fit. The physical meaning of this is not clear, but it seems to be related to the amorphous nature of the Cs,O layer. We conclude that the way to get lower electron transverse energy spread cathodes is to study alternative activation methods and new materials with smaller effective electron masses. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362992
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  • 2
    Electronic Resource
    Electronic Resource
    Physics of high-intensity nanosecond electron source: Charge limit phenomenon in GaAs photocathodes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7318-7323 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaAs negative electron affinity cathodes are used as high-intensity, short-time electron source at the Stanford Linear Accelerator Center. When the cathodes are illuminated with high-intensity laser pulses draw peak currents that are extremely high, typically of tens of Amperes. Because of the high currents, some nonlinear effects are present. Very noticeable is the so-called charge limit (CL) effect, which consists of a limit on the total charge in each pulse; that is, the total bunch charge stops increasing as the light pulse intensity increases. The CL effect is directly related to a photovoltage built up in the surface as a consequence of the photoelectrons coming from the bulk. We discuss possible ways to minimize the formation of the surface photovoltage. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361448
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanism for nearly ohmic behavior in annealed Au/n-GaAs Schottky diodes (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 711-715 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The origin of the ohmic behavior observed after annealing Au/n-GaAs {110} Schottky diodes was investigated by electron-beam-induced current (EBIC) measurements of diode plan views and cross sections, combined with standard scanning electron microscopy and transmission electron microscopy techniques. The large leakage currents responsible for this behavior arise at the periphery of the deposited gold films, where elongated gold crystallites which lie on the GaAs surface are observed after heat treatment. These crystallites are typically 2–5 μm long, 500–2000 A(ring) wide, and are crystallographically oriented along the GaAs [110] direction. EBIC imaging demonstrated that a space-charge region was present under the peripheral area showing the gold crystallites. Comparison of current collection as measured with EBIC between annealed and unannealed diodes shows a large reduction in current collection under and around the periphery of the annealed diodes. These data allow attribution of the ohmic behavior to a recombination current. Experiments done with overlapping Au evaporations show that recombination on the bare GaAs surface between the observed crystallites surrounding each annealed diode is the main component of this recombination current, and thus of the large leakage current.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343543
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  • 4
    Electronic Resource
    Electronic Resource
    Engineered Schottky barrier diodes for the modification and control of Schottky barrier heights (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 5159-5169 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique for fabricating controlled Schottky barrier heights to GaAs over the entire band gap is demonstrated. Thin, highly doped semiconductor layers at the metal-semiconductor interface allowed the reproducible control of the effective barrier height on n-type GaAs from near zero (i.e., ohmic behavior at 300 K) to 1.33 eV (the band gap equals 1.43 eV at 300 K) with diode ideality factors 1.02≤n≤1.21. Molecular-beam epitaxy was used to grow GaAs epitaxial layers with in situ deposited Al metal layers, resulting in diodes with nearly ideal electrical and structural characteristics. Electrical characterization by current-voltage (I-V) and capacitance-voltage (C-V) techniques, models for these I-V and C-V characteristics, and structural characterization by high resolution transmission electron microscopy lattice images are presented. Implications of this work for models of Schottky barrier formation are discussed, as well as some applications for these "engineered Schottky barrier diodes.''
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338290
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  • 5
    Electronic Resource
    Electronic Resource
    Comparative study of Fermi energy pinning and adatom bond character: Antimony versus the column 3 elements (Al, Ga, In) on GaAs (110) and GaSb (110) (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 5089-5092 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New results which probe the nature of a defect mechanism responsible for pinning the Fermi energy within the band gap on the (110) surfaces of the 3-5 compounds are presented. From these results it is concluded that to first order the Fermi energy pinning position is independent of the fundamental difference between the Sb-GaAs chemical bond and the column 3 metal-GaAs bond. Furthermore, based on the defect mechanism for the Schottky barrier formation proposed by Spicer and Lindau, the present data can be most easily understood if the defect is more complex than a single surface lattice vacancy. Previously, investigations of column 3 metals on both n- and p-type GaAs, by photoemission electron spectroscopy, revealed a systematic difference in surface Fermi energy stabilization in the gap, with p-type samples pinning 0.25 eV below n-type samples. In the present work, it is shown that antimony, a column 5 element, yields essentially the same Schottky barrier height as the column 3 metals when adsorbed on GaAs (110). A strong similarity in the barrier height is also noted when Sb adsorption is compared to Ga adsorption on GaSb (110). The observed tendency for n-type GaSb to pin closer to the valence-band maximum than GaAs is consistent both with the Spicer/Lindau defect mechanism and with the "anion rule'' of McCaldin, McGill, and Mead. These results are important for the theory of Schottky barrier formation and for Schottky barrier device fabrication.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335293
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  • 6
    Electronic Resource
    Electronic Resource
    Annealing of intimate Au-GaAs Schottky barriers: Thick and ultrathin metal films (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 1247-1251 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using valence-band and core-level photoemission spectroscopy (PES) and electrical device measurements, the effects of annealing on Au:n-type (110) GaAs Schottky diodes fabricated in ultrahigh vacuum have been studied. Similiar trends in the annealing-induced changes in the barrier height of Au:n-type GaAs were found for 0.2 and 15 monolayer coverages as determined by PES and for thick film coverages (1000 A(ring)) as determined by current-voltage (I-V) and capacitance-voltage (C-V) measurement techniques. In each case, the barrier height was found to be stable for temperatures between 30 and 200 °C and between 300 and 500 °C; while a gradual decrease in the barrier height was found for annealing temperatures of 200–300 °C. These changes are correlated with the formation of a Au-Ga rich layer at the interface during anneals at 200 to 300 °C. Leakage currents were found to dominate the I-V characteristics in the devices which were annealed above the Au-Ga eutectic temperature. These peripheral leakage currents were eliminated by mesa-etching the devices. This allowed more reliable barrier height determinations using device measurements for higher annealing temperatures than has been previously reported for the Au-GaAs system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.334521
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  • 7
    Electronic Resource
    Electronic Resource
    Interaction of overlayers of Al and Rb with single-crystalline surfaces of Bi2Sr2CaCu2O8 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2667-2670 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoemission results from Al and Rb interfaces with single crystals of Bi2Sr2CaCu2O8 high-temperature superconductors are reported. The Al and Rb adsorbates are found to react quite differently with the Bi2Sr2CaCu2O8 substrate. While adatoms of Rb significantly affect only the Bi and O atoms in the top atomic layer, the Al adsorbate profoundly disrupts the bonding character of the whole Bi2Sr2CaCu2O8 material. For Al, the Bi and Cu states are strongly reduced, and the Sr and O states show evidence of oxidized components. In addition, Al causes a strong out-diffusion of oxygen from the bulk. The differences in the reactivity of Al and Rb are discussed in terms of the different mobility of the two atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345480
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  • 8
    Electronic Resource
    Electronic Resource
    Aging of Schottky diodes formed on air-exposed and atomically clean GaAs surfaces: An electrical study (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 2006-2010 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this report we show that the application of a large voltage and current stress can significantly change the barrier height of a given metal (Ag,Al,Au,Pd,Cr)/GaAs(110) contact. These changes of barrier height depend on the metal used, the method of fabrication of the diode (air exposed or UHV cleaved), and the intensity and direction of the potential and current during the electrical aging. In particular, the air-exposed Ag diodes exhibit the largest change in the barrier height (∼85 meV) upon aging, while the UHV-cleaved Ag diodes do not exhibit a significant change. In the case of Au, both UHV-cleaved and air-exposed diodes show a small change (∼20 meV). The barrier heights of Pd, Al, and Cr air-exposed diodes do not exhibit an appreciable change upon aging (i.e., 〈10 meV). The changes in barrier height are found to have a very consistent and characteristic logarithmic dependence upon time. Once the electrical aging is stopped, the barrier height is found to recover to near the unaged value. The long time constant of the aging process, the ability of the barrier height to recover after aging, the long time constant of the recovery process, and the acceleration of the recovery process by illumination suggest that the changes in the barrier height which occur upon electrical aging are due to the creation and/or annihilation of deep level traps near the interface. We also report a systematic study of a comparison of barrier height determinations for Ag, Al, Au, Cr, and Pd diodes formed on air-exposed and UHV-cleaved GaAs(110) surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341178
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  • 9
    Electronic Resource
    Electronic Resource
    Electronic structure of the gold/Bi2Sr2CaCu2O8 and gold/EuBa2Cu3O7−δ interfaces as studied by photoemission spectroscopy (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 307-309 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution photoemission has been used to probe the electronic structure of the gold/Bi2Sr2CaCu2O8 and gold/EuBa2Cu3O7−δ interface formed by a low-temperature (20 K) gold evaporation on cleaved high quality single crystals. We find that the metallicity of the EuBa2Cu3O7−δ substrate in the near surface region (∼5 A(ring)) is essentially destroyed by the gold deposition, while the near surface region of Bi2Sr2CaCu2O8 remains metallic. This has potentially wide ranging consequences for the applicability of the different types of superconductors in real devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104219
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  • 10
    Electronic Resource
    Electronic Resource
    Vacuum ultraviolet photoelectron spectroscopy of (NH4)2S-treated GaAs (100) surfaces (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 861-863 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface chemistry and band bending of the ammonium sulfide-treated GaAs (100) surface has been studied using surface-sensitive synchrotron radiation photoemission spectroscopy. We find that the treatment leaves the GaAs surface terminated with roughly a monolayer of sulfur bonded to both As and Ga atoms. An n-type barrier height of 0.8 eV is measured. The thermal stability of the various chemical components is studied and various issues of the passivating mechanism are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101780
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