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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5084-5089 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Photoreflectance spectra have recently been obtained for a range of single strained Si1−xGex epilayers for 0.12〈x〈0.24, which are buried under a Si cap. Spectra measured at different positions on a sample wafer showed pronounced changes in the SiGe line shape. Here these changes are shown to be due to phase shifts arising from changing optical interference effects caused by variations in the Si cap thickness. The phase shifts are determined accurately using a Kramers–Kronig analysis and are interpreted in terms of a multiple-reflection treatment incorporating a calculation of the Seraphin coefficients. This allows the Si cap thiakness changes to be determined and compared to the0results of speatroscopic ellipsometry measurements. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2672-2678 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Room-temperature photoreflectance measurements of a GaAs/Al0.2Ga0.8As single-quantum well structure showed well defined Franz–Keldysh oscillations in the neighborhood of the GaAs and Al0.2Ga0.8As band-edge energies. That experiment investigated the origin of the Franz–Keldysh oscillations by sequential etching and photoreflectance analysis of the grown layers and showed that the phase of the Franz–Keldysh oscillations shifted as the upper Al0.2Ga0.8As barrier was etched, with eventual phase reversal when roughly half of the upper barrier was removed. Here, these phase shifts are determined accurately using a novel Kramers–Kronig approach and they are interpreted in terms of optical interference effects using both a simple two-ray model and a multiple-reflection treatment incorporating a calculation of the Seraphin coefficients. The results also enable the thickness of the layers removed to be determined. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4338-4347 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report a detailed analysis of room-temperature photoreflectance data of four InxGa1−xAs/AlyGa1−yAs undoped strained single quantum wells with x≈0.20 and y≈0, 0.05, 0.10, and 0.20. We have compared our results with theoretical calculations based on an effective mass formalism, where possible variations of well and barrier composition and thickness have been included. For all the samples studied we have identified both allowed and forbidden transitions in the spectra and obtain good fits assuming a conduction-band offset Qc of 60%±5%. This detailed analysis shows for the first time that room-temperature photoreflectance measurements alone can be used to determine the well composition and thickness together with the barrier composition and the barrier offset. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4285-4287 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Photoreflectance spectra have been obtained from single strained Si1−xGex epilayers (0.12〈x〈0.24) buried under a silicon cap. Despite dramatic changes in the shape of photoreflectance spectra obtained at different positions on a sample wafer, which are explained in terms of a strong interference effect as the Si cap thickness varied, spectra were fitted adequately using three Lorentzian oscillators. Critical point transition energies calculated in this way were consistent with E1 and E1+Δ1 in Si1−xGex and E′0 in silicon and allowed for determination of composition to within x±1.5%. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6472-6480 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experimental results are presented for the physical origins of room-temperature photoreflectance features of a AlGaAs/GaAs single-quantum well structure. The spectra exhibit well-defined Franz–Keldysh oscillations which overlap with photoreflectance features due to the quantum well and complicate the determination of the energies of the transitions within the quantum well. The origin of the Franz–Keldysh oscillations are determined using wet chemical etching to selectively remove grown layers down to the substrate. The resulting spectra are presented as a function of etch depth which allows the magnitude of the built-in electric fields to be determined and reveals the location within the quantum well structure where the Franz–Keldysh oscillations originate. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3092-3099 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Room temperature photoreflectance (PR) has been performed on three In0.32Ga0.68As/ In0.76Ga0.24As0.53P0.47 tensiley strained single-quantum-well structures, with heavy Zn modulation p-doping (5×1017 cm−3) in the quaternary barriers, which are lattice matched to an InP substrate. The PR spectra exhibit strong, well-defined, and regular Franz–Keldysh oscillations (FKO) associated with the barrier layers. We study the FKO in detail, comparing two different techniques of analyzing them to obtain a measure of the built-in electric field: (i) the conventional simple graphical asymptotic technique; and (ii) least-squares fitting to the experimental spectra using the recently proposed electromodulation model based on complex Airy functions. In the second method, the PR spectra are best described by the sum of two Airy function expressions representing degenerate heavy- and light-hole band edges. Good fits are obtained without the need to use an empirical energy-dependent broadening term to account for the effects of nonflatband modulation and nonuniform fields. The results are consistent with FKO originating from heavy- and light-hole transitions under the same electric field, but having a partial destructive interference effect in the PR spectrum. The fitted field value of ∼17 kV/cm is essentially the same as that obtained in the graphical analysis which assumed that the FKO were heavy-hole dominated. However, contrary to previous suggestions, neither the heavy- nor light-hole contributions dominate the actual FKO spectrum. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 4909-4917 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Room temperature photomodulated reflectance (PR) and double crystal x-ray diffraction (DCXRD) measurements have been performed on a series of tensilely strained InxGa1−xAs multiple quantum well (QW) laser structures, with In0.80Ga0.20As0.43P0.57 barriers, which are lattice-matched to an InP substrate. Seven samples are studied, with nominal QW In composition varying between x=0.533 and 0.316, corresponding to biaxial tensile strains between 0% and 1.5%, respectively. The DCXRD measurements provide accurate information on composition, strain and layer thickness, while the PR yields the energies of both allowed and forbidden critical point interband QW transitions, and how these vary with strain, particularly the transitions between the ground-state conduction band and heavy/light hole valence band levels. A three-band effective mass formalism is used to model the QW transitions and very good agreement with the PR measurements is obtained once excitonic binding energies, and the quantum confined Stark effect are taken into account. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3268-3270 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Photomodulated reflectance (PR) spectra have been measured for self-assembled InAs/GaAs quantum dot (QD) structures consisting of a pair of QD layers, with a GaAs spacer either 50 or 100 Å thick. The PR clearly reveals five confined-state QD transitions, at both 80 and 300 K, as well as features from the two-dimensional confining and GaAs layers. The measured QD transition energies correlate well with photoluminescence spectra at 13 K, using high laser excitation powers to incur level filling. Annealing one of the samples produces a strong blueshift in the QD transitions. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4277-4279 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report electromodulated reflectance studies on the band structure of a dilute-N (∼1%) (GaIn)(NAs)/GaAs/AlAs vertical-cavity surface-emitting laser (VCSEL), as a function of temperature and incidence angle. The wide range of operating temperatures observed for this type of VCSEL (∼360 K here) is due to the reduced temperature variation of the effective band gap of the active (GaIn)(NAs) quantum wells, and broad gain. By comparing lasing properties and band structure we argue that the gain broadening is not simply due to alloy disorder but arises from a recently-proposed intrinsic property of (GaIn)(NAs): the existence of different band gaps for the five possible nearest-neighbor configurations of the N substitutional impurity. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Polymer bulletin 18 (1987), S. 155-158 
    ISSN: 1436-2449
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Summary The Brillouin spectrum of polyethylene has been measured as a function of temperature. Slope discontinuities of opposite directions have been observed in the Brillouin shift and width near the glass transition temperature. The former is attributed to a corresponding discontinuity in the temperature coefficient of specific volume, while the latter to the onset of long-range coordinated molecular motion near the transition region.
    Materialart: Digitale Medien
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