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  • 1
    Electronic Resource
    Electronic Resource
    Compositional analysis of molecular beam epitaxy grown InyGa1−yAs/GaAs/AlxGa1−xAs quantum wells by determination of film thickness (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3820-3826 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thickness of the individual layers of molecular beam epitaxy grown pseudomorphic InyGa1−yAs (0.1≤y≤0.35)/GaAs/Al0.3Ga0.7As quantum well structures has been determined by transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS) depth profiling, and reflection high energy electron diffraction (RHEED) with the aim of the compositional analysis of the ternary alloy films. Agreement between SIMS and TEM thickness data within 15% is found. Reliable RHEED data at y≥0.25, where the number of RHEED oscillations is drastically reduced by the three-dimensional growth of the InGaAs film, have been obtained by averaging repeated RHEED measurements. As compared with TEM, RHEED tends to lower values by 10% at maximum. The compositional data determined by the different methods including also photoluminescence (PL) agree within 20% in the technologically important region y≥0.2. At y=0.1, extreme accuracy requirements concerning the thickness determination limit the accuracy of SIMS and TEM to around 30%. Therefore PL and RHEED are superior at this concentration. An influence of the growth temperature on the In content at y=0.3 could be detected only by PL, demonstrating the excellent relative accuracy of PL.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352889
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of In on Si local vibrational modes in InxGa1−xAs (0≤x≤0.12) (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7797-7804 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local vibrational modes (LVM) of Si in substitutional sites have been observed by resonant Raman spectroscopy in highly doped (≥8×1018 cm−3) InxGa1−xAs layers, either relaxed or under strain, on [100] GaAs substrates. The peak frequency ωLVM of the Si on Ga site (SiGa) LVM in unstrained samples shifts to lower values with increasing In content. For x≤0.10 this shift is clearly higher than expected from a linear interpolation between the measured values in the binaries. The comparison between the SiGa peak frequency measured in both a full strained layer and a relaxed layer with similar composition provides a rough determination of the deformation potentials for the SiGaLVM in these layers: q/ω2LVM=−2.7±1 and p/ω2LVM=−2.5±1. As the In content becomes higher the width of the SiGa peak increases much more than that of the GaAs-like longitudinal optical-phonon peak, revealing the splitting due to the loss of local symmetry introduced by the In. New calibration factors for the Si-defect concentrations have been deduced, which allow estimation of the solubility limit for the Si incorporation in substitutional positions, which ranges from 2.3×1019 to 2.6×1019 cm−3 for the layers at the growth conditions used. The analysis of the integrated intensity of the LVM Raman peaks indicates that the degree of electrical compensation is clearly reduced for increasing In up to x≤0.05, due to both an increase of the solubility limit for Si in these layers and a saturation or slight reduction of the SiAs-related defect concentrations. This conclusion is also supported by Hall and plasmon measurements. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358521
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  • 3
    Electronic Resource
    Electronic Resource
    Intersubband transitions in partially interdiffused GaAs/AlGaAs multiple quantum-well structures (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2195-2199 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Continuous tuning over the entire 8–12 μm wavelength range is demonstrated for the intersubband absorption resonance in n-doped GaAs/AlxGa1−xAs multiple quantum-well structures following partial interdiffusion of the well and barrier layers via rapid thermal annealing. The data indicate that redshifting of the intersubband absorption resonance arises both from interdiffusion-induced modification of the confining potential and from a decrease in the depolarization shift. The latter effect is due in part to a decrease in the free-carrier concentration within the Si-doped quantum wells following rapid thermal annealing. Significant diffusion of the localized Si dopant is also observed over the range of annealing temperatures investigated here. Calculated values of the Al-Ga interdiffusion coefficient, as a function of anneal temperature, indicate that Si diffusion through the heterointerfaces contributes substantially to layer intermixing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350334
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  • 4
    Electronic Resource
    Electronic Resource
    Quantitative assessment of Be acceptors in GaAs by local vibrational mode spectroscopy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 971-974 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Be-doped epitaxial layers of GaAs grown by molecular beam epitaxy have been studied by local vibrational mode spectroscopy combining infrared absorption and Raman scattering. Calibration factors for both experimental techniques have been derived which enable quantitative assessments to be made of the concentrations of Be acceptors in GaAs. In Raman spectroscopy the detection limit is ≈ 3×1018 cm−3 for as-grown layers only 10 nm in thickness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347289
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  • 5
    Electronic Resource
    Electronic Resource
    Raman spectroscopic assessment of carbon-hydrogen pairs in carbon-doped GaAs layers (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2546-2548 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman scattering by local vibrational modes of carbon-hydrogen pairs is reported for heavily carbon-doped epitaxial GaAs layers. Scattering by the longitudinal carbon mode of these pairs at 452 cm−1 shows a strong resonant enhancement for incident photon energies approaching the E1 band-gap energy of GaAs ((approximately-equal-to)3 eV). A possible mechanism for this resonance behavior is discussed in terms of the displacement of the carbon atom from its normal arsenic lattice site accompanied by a lengthening and weakening of the carbon-gallium bonds when carbon-hydrogen pairs form. The present findings demonstrate that resonant Raman scattering is an attractive tool for the detection of carbon-hydrogen pair formation in thin carbon-doped epitaxial GaAs layers grown from source materials containing hydrogen. The detection limit is estimated to be in the low 1018 cm−3 range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106908
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  • 6
    Electronic Resource
    Electronic Resource
    Redistribution of epitaxial Si on (001) GaAs during overgrowth by GaAs (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2730-2732 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We examine the stability of pseudomorphic submonolayer Si films embedded in (001) GaAs by molecular-beam epitaxy. Secondary ion-mass spectrometry depth profiling reveals the presence of 1019 Si-atoms/cm3 in the first 40 nm of the GaAs cap layer. The systematic investigation of samples having different cap thickness by Hall effect measurements and local vibrational mode Raman spectroscopy allows us to identify the site distribution of Si atoms in the cap layer and yields insight into the migration mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105898
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of low energy laser on the growth and regeneration of capillaries (1990)
    Springer
    Lasers in medical science 5 (1990), S. 381-386 
    Details
    ISSN: 1435-604X
    Keywords: HeNe laser irradiation ; Biostimulation ; Wound healing ; Capillary regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Laser light of low energy is discussed to have an accelerating effect on wound healing. The aim of the present study was to proof whether HeNe laser irradiations have a positive effect on regeneration of capillaries. For this purpose aluminium chambers were implanted in the dorsal skin flap of Syrian hamsters. After coagulation of blood vessels by means of an argon laser the tissue was irradiated daily with the low energy light of a HeNe laser. Regeneration of capillaries was studied by means of intravital microscopy. The results of the study revealed a positive effect of low dose HeNe laser irradiation on the regeneration of capillaries at day 5 after the coagulation. The measurable part of the capillaries was about 27% higher for the irradiated animals compared to controls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02032595
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of conducting GaAs multilayers by infrared spectroscopy at oblique incidence (1990)
    Springer
    Applied physics 50 (1990), S. 7-12 
    Details
    ISSN: 1432-0630
    Keywords: 78.20 ; 78.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The electrical and geometric properties of GaAs multilayer structures are measured nondestructively by infrared reflectance spectroscopy (50–5000 cm−1). Using oblique incidence and both s- and p-polarizations of the probing beam, carrier concentration and thickness of the epitactic films as well as the carrier concentration of the GaAs substrate are determined. The main structures in the spectra are due to phonon reststrahlen bands, Fabry-Perot interferences and the zeros of the dielectric function leading to dips in the reflectance (Berreman Mode). The results compare favorably with a depth-resolved secondary ion mass spectrometric (SIMS) sample analysis. The range of applicability of the method is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323946
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  • 9
    Electronic Resource
    Electronic Resource
    Electric field effects on persistent spectral holes: Perylene in the polar polymer polyvinylbutyral (1990)
    Springer
    Applied physics 51 (1990), S. 336-341 
    Details
    ISSN: 1432-0649
    Keywords: 78.50.−w ; 61.40.−a
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigated the effects of an electric field on a spectral hole burned in the inhomogeneously broadened S 0–S 1 transition of perylene in different samples of the polar polymer polyvinylbutyral (PVB) and in cellulose nitrate. The spectral hole is broadened and reduced in depth by the electric field. It was checked experimentally for perylene in PVB that the hole area remains constant when an electric field is applied. We determined the effective matrix-induced electric dipole moment differences δμ* for perylene in different PVB samples and in cellulose nitrate. Within experimental accuracy the value of δμ* is approximately independent of the composition of PVB and its water content. For perylene in cellulose nitrate the value of δμ* is larger by a factor of 1.5 than in PVB. The results are discussed on the basis of a simple model for the electric field effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00348970
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  • 10
    Electronic Resource
    Electronic Resource
    Some costs of reproduction for male bushcrickets, Requena verticalis (Orthoptera : Tettigoniidae) allocating resources to mate attraction and nuptial feeding (1992)
    Springer
    Behavioral ecology and sociobiology 31 (1992), S. 57-62 
    Details
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cost of reproductive effort is known to result in a trade-off between current and future reproduction. Similarly, trade-offs in energy allocation may occur between components of reproductive effort, mating and parental effort, within a single reproductive episode. We investigated the energy allocated to mating effort (calling to attract females) and parental effort (donation of spermatophore nutrients at mating) by male bushcrickets, Requena verticalis, under two dietary regimes. Males provided with a low quality diet reduced the daily energy allocated to calling activity while maintaining their investment in spermatophores. Males provided with a high quality diet did not allocate more resources per day to their spermatophores but stored excess energy for future reproduction. Thus, on a per day basis, males appear to hold constant their investment in the spermatophore at the cost of reduced mating effort when resources are limited. Males on both diets, however, increased the size of their spermatophore donations when the interval between female encounters was increased. One explanation for this pattern could be a frequency-dependent optimization of spermatophore size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167816
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