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  • 1995-1999  (8)
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  • 1
    Electronic Resource
    Electronic Resource
    Photoreflectance study of Si delta-doped low-temperature GaAs grown by molecular beam epitaxy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2124-2127 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoreflectance spectroscopy has been used to study the surface electric field of Si delta-doped GaAs grown by molecular beam epitaxy at a low substrate temperature (230 °C). Franz–Keldysh oscillations in the reflectance spectra are observed for samples annealed above 700 °C for 10 min. The deduced surface electric field increases with annealing temperatures and with a decrease in spacer thickness between surface and the delta-doped plane. The evolution of photoreflectance spectra can be explained by the activation of Si donors and Fermi level pinned at surface due to the redistribution of As precipitates. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358788
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  • 2
    Electronic Resource
    Electronic Resource
    The Fermi level of annealed low-temperature GaAs on Si-δ-doped GaAs grown by molecular beam epitaxy (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 486-490 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoreflectance has been used to study the Fermi level of annealed low-temperature GaAs in sample structures composed of low-temperature GaAs on top of Si-δ-doped GaAs. The diffusion of As precipitates across the interface between low-temperature GaAs and normal GaAs is observed by cross-sectional imaging via transmission electron microscopy. We have calculated the Fermi-level pinning in low-temperature GaAs by including the Si-δ-doped carrier concentration correction due to the accumulation of As precipitates. The Fermi level is found to decrease from 0.7 to 0.5 eV below the conduction band when the annealing temperature is increased from 600 °C to 900 °C. This may be explained with the buried Schottky barrier model. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366719
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  • 3
    Electronic Resource
    Electronic Resource
    A study of the Franz–Keldysh oscillations in electromodulation reflectance of Si-delta-doped GaAs by a fast Fourier transformation (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7873-7878 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The line shapes of electromodulation spectra exhibit extended Franz–Keldysh oscillations and interference beats in the presence of a uniform built-in electric field. For this work, we used photoreflectance and contactless electroreflectance to study the Franz–Keldysh oscillations in Si-delta-doped GaAs. The fast Fourier transformation taken to the photoreflectance and contactless electroreflectance spectra, produced more complicated results than were observed in previous studies, when the effect of the modulation field is nonnegligible. This indicates that the interference beats are not only due to different effective heavy-hole and light-hole mass but also to the modulation field. We propose that the Franz–Keldysh oscillations generally contain four frequencies, which correspond to the heavy-hole and light-hole splitting. A comparison between the experiments and some numerical simulations attest to the validity of our proposal. This line shape analysis could then be applied to estimate the strength of a modulation field in contactless electroreflectance and photoreflectance. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367964
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  • 4
    Electronic Resource
    Electronic Resource
    Pumping-beam-induced photovoltaic effect on the photoreflectance of a δ-doped GaAs film (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6980-6983 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoreflectance (PR) spectroscopy of a δ-doped GaAs film has been measured at 300 K. Results reveal many Franz–Keldysh oscillations (FKOs) above the band-gap energy, which will enable the electric-field strength to be determined from the periods of FKOs. Since the photovoltaic effect cannot be neglected in PR measurements when using light as both the pumping and probing beams, it is generally assumed that the modulation field δF is much smaller than the built-in field F so that the periods of the FKOs will not be affected by the pumping beam. However, the induced photovoltage can be over 2/3 of Fermi level at low temperatures and cannot be neglected even at room temperature. Hence, the finite value of δF needs to be taken into consideration. The effect of δF on the shapes of PR is discussed, and it is shown that the FKOs of PR oscillate at a frequency corresponding to F−δF/2. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363771
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  • 5
    Electronic Resource
    Electronic Resource
    Fast Fourier transformation of piezoreflectance in δ-doped GaAs (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 1074-1080 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Franz–Keldysh oscillations in Si-δ-doped GaAs have been studied by the application of fast Fourier transformations to the piezoreflectance spectra. In such studies, we find that the Franz–Keldysh oscillations of the piezoreflectance and its associated Fourier transformation can be described by a model calculation which considers the energy gap modulation in a uniform electric field. Owing to the character of nonelectromodulation, the Franz–Keldysh oscillation lineshape in the piezoreflectance has no modulation electric field distortion such as that which occurs in the photoreflectance and electroreflectance experiments. We demonstrate that the piezoreflectance accuracy is better than the photoreflectance or electroreflectance for the measurement of a uniform built-in electric field. The fast Fourier transformation of piezoreflectance spectra exhibits two separate heavy- and light-hole frequencies at temperatures from 20 to 425 K. Using these separated peaks, the ratio between the heavy- and light-hole effective reduced mass, the surface Fermi level, and the broadening parameters of the Franz–Keldysh oscillations are measured and discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368106
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  • 6
    Electronic Resource
    Electronic Resource
    Electromodulation reflectance of low temperature grown GaAs (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 2603-2606 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied low temperature grown GaAs by electromodulation reflectance spectroscopy for growth temperatures between 200 and 320 °C. The reflectance spectra can be observed only when the concentration of the arsenic antisite defect is lower than 3.4×1019 cm−3. The absence of the signal for a rich defect sample is related to the short carrier lifetime and surface depletion width. The transition energies of E0 and E1 are found to increase with the decrease of the growth temperatures. The increase of the transition energies is attributed to lattice mismatch and deviation of the stoichiometry. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366073
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  • 7
    Electronic Resource
    Electronic Resource
    Microstructural characterization of interfacial reaction products between alumina and braze alloy (1995)
    Springer
    Journal of materials science 30 (1995), S. 1679-1688 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The Al2O3/STS304, Al2O3/Cu and Al2O3/Al2O3 joints were brazed in vacuum with three types of Cu-Ag-Ti brazing filler metals at 1193 K for 1.2 ks. The effects of adherend metals on the microstructure and microchemistry of reaction products formed at the Al2O3/filler metal interface have been investigated. The reaction products of A2O3/STS304 joints showed a layered structure consisting of TiO (monoclinic, a 0=0.585 nm, b 0=0.934 nm, c 0=0.414 nm), Cu2Ti4O (cubic, a 0=1.149 nm) and Fe2Ti4O (cubic, a 0=1.1297 nm). The TiO compound is a nonstoichiometric titanium monoxide with composition range of TiO0.9 to TiO1.1. Cu2Ti4O and Fe2Ti4O compounds can be considered as (Cu, Fe)2Ti4O because both of them have nearly the same crystal structure and lattice constants. The reaction products of Al2O3/Cu and Al2O3/Al2O3 joints also showed a layered structure consisting of TiO and Cu2Ti4O. The TiO compound was formed by redox reaction between Al2O3 and segregated titanium, whereas Cu2Ti4O and Fe2Ti4O compounds formed by solid-state reaction between TiO and copper from the brazing alloy and iron from the adherend metals, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00351596
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  • 8
    Electronic Resource
    Electronic Resource
    On-line state estimation of biomass based on acid production in Zymomonas mobilis cultures (1998)
    Springer
    Bioprocess engineering 18 (1998), S. 329-333 
    Details
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The concentrations of biomass, substrate and product are very important state variables of almost every bioprocess and generally unable to be measured directly in␣situ due to the lack of reliable sensors. In this paper, an adaptive observer of the biomass concentration is proposed for an anaerobic fermentation process where only the measurement of the acid product is available on-line. The observer was tested to be effective by several experiments under various operating conditions. In this experimental system, an auto-sampling device was connected between the bioreactor for the fermentation of Zymomonas mobilis and a HPLC so that the concentrations of glucose and ethanol could be directly measured through such implementation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008992
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