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  • 1
    Electronic Resource
    Electronic Resource
    N-induced vibrational modes in GaAsN and GaInAsN studied by resonant Raman scattering (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5027-5031 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vibrational modes introduced by the incorporation of N into GaAs and GaInAs have been studied by Raman spectroscopy on samples grown by molecular-beam epitaxy using a rf nitrogen plasma source. When proceeding from GaAs1−xNx to Ga1−yInyAs1−xNx with x≤0.04 and y≤0.12, the nitrogen-induced vibrational mode near 470 cm−1 observed in GaAsN was found to broaden and to split into up to three components with one component at a frequency higher than that of the Ga–N mode in GaAsN. This observation shows that the incorporation of In into GaAsN strongly affects the local bonding of the N atoms by changing the local strain distributions as well as the formation of a significant fraction of In–N bonds. The resonant enhancement in the scattering cross section of the Ga–N vibrational mode, observed in low N-content GaAs1−xNx (x(approximate)0.01) for incident photon energies matching the mostly N-related E+ transition at around 1.8 eV, was found to broaden significantly upon increasing N content as well as upon the addition of In to form GaInAsN. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1412277
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  • 2
    Electronic Resource
    Electronic Resource
    Γ- and X-band contributions to nonresonant tunneling in GaAs/Al0.35Ga0.65As double quantum wells (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2517-2519 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-resolved photoluminescence in the picosecond regime is performed on an asymmetric GaAs/Al0.35Ga0.65As double quantum well structure with a barrier thickness of 6 nm to obtain the Γ- and X-point barrier contributions to nonresonant tunneling. Application of hydrostatic pressure up to 37 kbar at 5 K reveals that tunneling via virtual X states is at least 800 times less efficient than via virtual Γ states. Above 24.5 kbar an extremely fast scattering of electrons out of the n=1 quantized level of the narrower quantum well is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101994
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  • 3
    Electronic Resource
    Electronic Resource
    Anisotropic electrical conduction in GaAs/In0.2Ga0.8As/Al0.3Ga0.7As strained heterostructures beyond the critical layer thickness (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2941-2946 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The anisotropic conduction of GaAs/In0.2Ga0.8As/Al0.3Ga0.7As inverted high-electron-mobility transistor (HEMT) structures has been investigated. The heterostructures were grown by molecular-beam epitaxy on (100) GaAs substrates. The thickness of the pseudomorphic layer was increased stepwise (150–300 A(ring)) beyond the critical layer thickness as determined by the appearance of misfit dislocations. These mixed 60° dislocations surrounded by depletion regions were observed as straight dark lines in cathodoluminescence. The measured resistance Rs was higher in the [01¯1] direction than in the perpendicular [011] direction. At T=30 K the conduction ratio of these two directions exceeded 105 in the 300-A(ring)-thick layer. The magnitude and anisotropy of Rs was correlated with the anisotropic dislocation patterns resulting from the preferential generation of the α dislocations (parallel) [011] as compared to the orthogonal β dislocations (parallel) [01¯1]. In both directions Rs depended exponentially on the number of dark lines perpendicular to the probing current. Simultaneously, the functional form of the temperature-dependent Rs(T) strongly varied with layer thickness. The thin, still elastically strained layers showed the usual behavior of HEMT structures. For the thicker layers a completely different temperature dependence was gradually developing, eventually leading to an exponential increase of Rs with inverse temperature between 300 and 100 K. Below this range Rs(1/T) changed more slowly and leveled off at 30 K. All these features are convincingly explained by a model assuming that the electrons can surmount the insulating depletion barriers in the conducting channel by a thermally induced tunneling mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351497
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of delta-doping profile and interface roughness on the transport properties of pseudomorphic heterostructures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 907-909 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thickness effects of the InGaAs channel on photoluminescence and transport properties of δ-doped Al0.3Ga0.7As/In0.3Ga0.7As heterostructures are investigated. The spreading of the Si δ-doping layer is deduced from a comparison of the measured charge with self-consistent calculations assuming a Gaussian Si distribution profile and a definite ionization probability of the Si-related DX centers. With decreasing channel thickness below 80 A(ring), the effect of the spreading on the sheet carrier concentration increases and the low temperature mobility decreases due to roughness scattering at the In0.3Ga0.7As/GaAs interface. In channels thicker than 80 A(ring) the thickness-independent alloy scattering process dominates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110992
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  • 5
    Electronic Resource
    Electronic Resource
    Investigation of DX centers in AlxGa1−xAs by space charge spectroscopy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1051-1056 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a critical analysis of both deep level transient spectroscopy and transient microwave absorption spectroscopy (MAS) for the case of DX centers in AlGaAs. We show that, even for a single level, a strongly nonexponential time dependence of the transients occurs. Our MAS experiments on Si-DX centers in Al0.3Ga0.7As extend the available data for the emission rates by more than three orders of magnitude. They are successfully interpreted by a single emission time constant using our model whereas at least three decay time constants are needed to explain the data by a pure exponential. Observed recapture processes in the neutral region of the sample underline the complexity of space charge spectroscopy in the case of the DX center.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354952
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  • 6
    Electronic Resource
    Electronic Resource
    Raman spectroscopic and Hall effect analysis of the free electron concentration in GaAs with ultrahigh silicon doping (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5023-5026 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Heavily silicon-doped GaAs grown by molecular beam epitaxy has been studied by combined coupled plasmon-phonon mode Raman spectroscopy and Hall effect measurements. Free electron concentrations up to 2×1019 cm−3 have been achieved with the dopant atoms being incorporated dominantly on Ga sites (≥90%) as measured by local vibrational mode Raman spectroscopy. To extract quantitative information from the plasmon-phonon Raman spectra, these spectra have been fitted using the temperature-dependent Lindhard–Mermin dielectric function including the nonparabolicity of the conduction band and wave vector nonconservation due to the absorption of the incident and scattered light. The excellent agreement found between Hall effect and Raman measurements demonstrates that consistent data on dopant incorporation and activation can be obtained, if band structure effects are accounted for appropriately in the analysis of the Raman spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353771
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Ion irradiation damage in n-type GaAs in comparison with its electron irradiation damage (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5593-5601 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In an effort to attain a better understanding of the nature of the defects introduced in GaAs by irradiating it with energetic light ions; electron or proton irradiated n-type GaAs samples, cut from the same layer grown by molecular-beam epitaxy, have been studied by deep level transient spectroscopy. By comparing the spectra, including the effects of high electric fields, and by using results for annealed samples, it is possible to determine which of the traps reported in electron irradiated GaAs, most of which are believed to be arsenic interstitial-vacancy pairs, are present in the proton irradiated material. The traps identified in proton irradiated GaAs include most of those found in electron irradiated material, either after irradiation or after irradiation and annealing. The results indicate that two of these traps are associated with defects which are more complex than simple interstitial-vacancy pairs. Two traps were found in proton irradiated material which have not been observed in electron irradiated GaAs. One of these is nearly as abundant as the prominent E3 center observed in electron irradiated GaAs and is probably also not a simple pair. The deep level transient spectroscopy peak for this trap is not clearly separated from that of E3 in proton irradiated GaAs. The other trap is probably associated with a particular impurity present in the MBE grown sample layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351958
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  • 9
    Electronic Resource
    Electronic Resource
    Extended supergravity: Chern–Simons theories in 2+1 dimensions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 239-246 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: In this paper de Sitter supergravity theories in 2+1 dimensions with positive cosmological constant as Chern–Simons gauge theories of the algebra OSp(M||2;C) are constructed. Starting from anti-de Sitter supergravity theories based on OSp(M||2;R)×OSp(M||2;R) algebras, a particular Inonu–Wigner contraction is used to construct a large class of super Poincaré supergravity theories with nontrivial internal symmetries. Other models based on algebras SL(M||N) and the exceptional super Lie algebras are also discussed. The classical consistency of our de Sitter supergravity theories is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529124
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  • 10
    Electronic Resource
    Electronic Resource
    Dielectric function spectra of GaN, AlGaN, and GaN/AlGaN heterostructures (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2779-2785 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pseudodielectric function spectra 〈ε〉 of wurtzite GaN, AlGaN, and GaN/AlGaN heterostructures were determined for photon energies ranging from 2 to 5 eV, using variable angle spectroscopic ellipsometry (SE). Samples were grown by low-pressure metalorganic chemical vapor deposition on c-plane sapphire substrates. The experimental 〈ε〉 spectra were analyzed using a multilayer approach, describing the dielectric functions of the individual layers by a parametric oscillator model. In this way, parametric dielectric function spectra of GaN and AlxGa1−xN (x≤0.16) were derived, as well as the composition dependence of the AlxGa1−xN band gap energy. The SE band gap data were found to be consistent with a bowing parameter close to 1 eV. Finally, the GaN and AlxGa1−xN parametric dielectric functions were used to quantitatively analyze the pseudodielectric function spectrum of GaN/AlGaN modulation doped field effect transistor structures, demonstrating the potential of SE in combination with a multilayer parametric dielectric function model for nondestructive ex situ control of GaN/AlGaN device structures. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1342022
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