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  • 1
    Electronic Resource
    Electronic Resource
    Ambipolar diffusion and carrier lifetime measurements in all-binary (InAs)2(GaAs)5 strained quantum wells grown on GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1868-1873 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The in-well ambipolar diffusion coefficients and carrier lifetimes in ordered all-binary quantum wells, composed of (InAs)2(GaAs)5 short-period strained-layer superlattices (SPSLSs) grown on [001]-oriented GaAs substrates, are measured using picosecond optically induced transient grating and pump-probe techniques. Quantum wells containing SPSLSs may be expected to exhibit higher in-plane hole mobilities compared to InGaAs ternary alloy quantum wells because of a larger average indium content and reduced disorder scattering in the SPSLS structures. The results obtained in the SPSLSs are compared to those obtained in InGaAs alloy quantum wells of comparable well width and confinement energies. This indicates that, for a given SPSLS and its equivalent alloy, the ambipolar diffusion coefficients are comparable while the carrier lifetimes in the SPSLSs are longer. The longer carrier lifetimes in the SPSLSs suggest that these binary structures possess fewer nonradiative recombination centers than the alloys. The absence of a dramatic improvement in the transport properties, however, may indicate that imperfect interfaces in the SPSLSs may be offsetting their possible advantages, in spite of the fact that optical measurements in the SPSLSs indicate high quality and x-ray and transmission electron microscopic measurements demonstrate the binary nature of these structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355301
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  • 2
    Electronic Resource
    Electronic Resource
    Temperature dependence of the Γ8v-Γ6c gap of GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2742-2747 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoluminescence (PL) peak positions of the ground state heavy and light-hole excitons on high-quality Molecular Beam Epitaxy grown GaAs/AlxGa1−xAs (x=0.3 and 1) multiquantum-well structures have been experimentally determined in the temperature range 4.2≤T≤340 K. Using these values and the well-known low-temperature energy of the GaAs Γ8V-Γ6C gap [EgΓ(GaAs,T=0 K)=1.5192 eV], we propose the temperature dependence to be EgΓ(GaAs,T)= 1.5192+5.16×10−5×T−1.99×10−6×T2 +2.60×10−9×T3 (EgΓ in eV). The nearly linear variation of EgΓ(GaAs,T) versus the temperature in the range 170 K≤T≤340 K can be approximated by a coefficient (dEgΓ/dT)=−4.4×10−4 eV/K, in excellent agreement with theoretical predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354674
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  • 3
    Electronic Resource
    Electronic Resource
    Room-temperature optical nonlinearities in strained (InAs)2(GaAs)5 superlattice quantum wells (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3243-3248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report room-temperature measurements of the nonlinear absorption cross section, σeh, and the nonlinear refraction coefficient, neh, associated with saturation of excitonic absorption and bandfilling, for high-quality multiple quantum well (MQW) structures in which each well consists of a highly strained, all binary (InAs)2(GaAs)5 short-period superlattice. The three samples studied, which have effective well thicknesses of 10.7, 14.8, and 18.8 nm, respectively, each display clearly resolved excitonic resonances at room temperature. Picosecond nonlinear transmission and transient grating measurements were performed on each sample in the spectral vicinity of the n = 1 heavy-hole excitonic resonance. The peak values of neh and σeh extracted from these measurements are comparable to those measured in high-quality GaAs/AlGaAs and unstrained InGaAs/InP MQWs. We determine the dependence of σeh and neh on the width of the quantum wells, and we discuss the fluence dependence of the nonlinearities. Consistency between the differential transmission and transient grating diffraction efficiency is demonstrated via a Kramers–Kronig analysis of the differential transmission spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348544
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  • 4
    Electronic Resource
    Electronic Resource
    Picosecond optical nonlinearities in a strained InAs/GaAs hetero n-i-p-i structure (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 929-932 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear optical properties of a n-i-p-i structure containing strained superlattice quantum wells in the intrinsic regions are studied using picosecond pump and probe pulses of the same photon energy. For pump fluences as low as 1.1 μJ/cm2, a blue shift of the excitonic resonance, caused by the screening of the built-in space-charge field and the accompanying reduction in the quantum-confined Stark effect, is clearly observed. At higher fluences, the onset of bleaching of the excitonic absorption is observed. The nonlinearities associated with the quantum confined Stark effect in the hetero n-i-p-i are directly compared to those arising from excitonic bleaching in identical strained superlattice quantum wells under flatband conditions. The picosecond time resolution allows a more accurate estimation of the carrier density in the hetero n-i-p-i by ignoring the density-dependent recombination and a quantitative comparison between the strength of the nonlinearities in the two structures. Although such comparisons depend on the optical fluence and structure of the hetero n-i-p-i, we find that the magnitudes of the nonlinearities in these two specific structures are comparable on a per carrier basis, although their spectral signatures are quite distinct.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351315
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  • 5
    Electronic Resource
    Electronic Resource
    Optical nonlinearities and ultrafast charge transport in all-binary InAs/GaAs strained hetero n-i-p-i's (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6891-6897 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use picosecond differential spectroscopy to temporally and spectrally resolve the formation and decay of nonlinearities and space-charge fields in a hetero n-i-p-i that contains quantum wells in the intrinsic regions that are composed of all-binary InAs/GaAs short-period strained-layer superlattices. The evolution of the optical response is determined by competition between excitonic bleaching and the excitonic shift caused by screening of the built-in electric field of the n-i-p-i. The relative contributions of the two resulting optical nonlinearities are complicated functions of fluence, time, and wavelength, with the detailed dynamics determined by thermionic emission from the wells, picosecond charge transport over nanometer dimensions, screening, and recombination. At low fluences, excitonic bleaching is the source of an ultrafast nonlinear response that can be turned on and off in 〈10 ps. This initial excitonic bleaching gives way to a blue shift of the exciton as the carriers escape the wells in ∼3 ps and drift to screen the built-in field in 〈10 ps. The blue shift persists until the carriers recombine nonexponentially on microsecond time scales. At higher fluences, excitonic bleaching and the blue shift are observed simultaneously, since only a fraction of the carriers are required to screen the field and the wells remain partially occupied. On the time scale of ∼10 ns, the bleaching contribution disappears as the carriers within the wells recombine, leaving only the persistent blue shift.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349813
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  • 6
    Electronic Resource
    Electronic Resource
    Collision energy dependence of Penning ionization electron spectra in crossed supersonic beams: He*(2 1S)+N2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5347-5348 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Penning ionization electron spectra are reported at five collision energies E in the range 1.6–4.9 kcal/mol. A preliminary analysis of the E dependence of the intensities, shapes, and positions of the vibronic lines reveals details of the ionization dynamics, features of the highly anisotropic potential surface, and connections with N2 orbital structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459655
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  • 7
    Electronic Resource
    Electronic Resource
    Observation of propagating collective excitations in liquid SO2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5387-5391 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectrum of collective excitations in liquid sulphur dioxide at two thermodynamic states has been measured by neutron triple-axis spectroscopy for momentum transfer ranges of 0.35≤Q≤2.0 A(ring)−1. Well-resolved inelastic peaks indicating the presence of propagating modes are found for Q values below 0.5 A(ring)−1 at T=266 K and below 0.7 A(ring)−1 at T=210 K. A precise value for the hydrodynamic limit has been found in both cases and the measured "dispersion relations'' are discussed in relation to predictions made by recent theoretical approaches.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461654
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  • 8
    Electronic Resource
    Electronic Resource
    Multichannel analysis of He*(21S)+Ne elastic and inelastic scattering in crossed atomic beams (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5963-5974 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State-to-state elastic and inelastic angular distribution and time-of-flight measurements are reported for the scattering of He*(21S) by Ne in crossed supersonic atom beams at four collision energies in the range 0.6–2.8 kcal/mol. The inelastic collision products He+Ne*(nl), where nl=3d', 4p, 4p', 5s, 5s', and 4d, are scattered predominantly forward with respect to the direction of incidence, except for endothermic states near threshold. The data are analyzed with a numerically exact multichannel curve-crossing model that yields good agreement with experimental cross section branching fractions and total quenching and state-to-state rate constants as well as the angular measurements. The model suggests the importance of intermediate "chaperone'' states, in which the excited electron is temporarily trapped in a d or f Rydberg Ne orbital, in channeling flux into the 4s' and 5s' upper laser states of Ne by energy transfer from He*(2s1,3S).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458367
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  • 9
    Electronic Resource
    Electronic Resource
    Reflection absorption infrared spectroscopy at the Daresbury SRS : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 1547-1550 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The high brilliance of modern synchrotron radiation sources results in a significant intensity advantage over conventional sources in the far infrared region of the spectrum. For applications with inherently low étendue, such as reflection absorption infrared spectroscopy (RAIRS) of surfaces, this advantage extends into the mid-infrared (IR) region, to 1000 cm−1 or higher. The spectroscopic region between 100 and 1000 cm−1 is of particular interest in surface science since it includes the vibrational modes of the majority of direct bonds between the surface and adsorbate, but the low intensity of conventional sources renders investigations of this region difficult. In this paper, we discuss the design criteria of the new Daresbury infrared beamline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143807
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  • 10
    Electronic Resource
    Electronic Resource
    Some special microwave structures for ECRIS : Proceedings of the 5th international conference on ion sources (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1125-1126 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The studies and the experimental work for constructing an electron cyclotron resonance ion source (ECRIS) for the new tritium linear accelerator (TRILAC) at the Institute of Atomic Physics are presented. The absence of consumable parts, the low neutral pressure, and the high ionization efficiency with light elements make ECRIS very attractive for this accelerator. Some special configurations for the microwave system and for the plasma chamber are presented. A suitable modified structure of a power helix-type traveling wave tube (glass envelope with helix) in conjunction with its corresponding lateral rectangular waveguide tapers is presented. Application of an iris-loaded circular waveguide (traveling wave structure of a linear accelerator) as a slow wave structure is also under study. Problems like unstable tuning and arcing, which are encountered in the known structures, could be avoided by using slow wave structures of traveling wave type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145085
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