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  • 1
    Electronic Resource
    Electronic Resource
    Raman study under resonant conditions of defects near the interface in a GaAs/Si heterostructure (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4777-4781 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Raman study has been performed, under resonant conditions, on a GaAs bevelled-edge layer grown on a Si substrate to characterize the optical and crystalline properties of the epilayer near the interface. According to the geometrical characteristics of the sample, a theoretical expression for the Raman intensities profile has been established and compared to the experimental data. This fitting procedure enables us to investigate the absorption coefficient of the GaAs layer due to the disorder-induced softening of the E1 edge. A quantitative analysis of the lattice disorder has been carried out on both longitudinal and transverse optical modes by studying the Raman line-shape evolution versus the laser spot position on the bevel edge. From this study, we have followed the recovery of the crystalline quality of the epilayer while going away from the interface, and evaluated the "Raman thickness'' of the dislocated layer. Using the spatial correlation model as a relationship between the disorder amount and the outcoming effects on the Raman line peaks, we have estimated the dislocation density at the heterostructure interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346133
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  • 2
    Electronic Resource
    Electronic Resource
    Generalization of Bragg reflector geometry: Application to (Ga,Al)As-(Ca,Sr)F2 reflectors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5366-5368 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bragg reflectors based on (Ca,Sr)F2 and (Ga,Al)As are studied. Modeling and fabrication of these structures by molecular-beam epitaxy were performed. Quarter-wave Bragg reflectors were found to present an excellent reflectance around the wavelength of interest, 870 nm, for only three periods of bilayers. However, the structures grown exhibited cracks after epitaxy due to thermal stress between both materials. To alleviate this problem, other reflector geometries were investigated consisting of deviations from the classical Bragg reflector. The new geometries enable one to reduce the absolute or relative fluoride thickness within the structure. The results obtained show that the use of adequate geometries allows one to overcome the stress problem, and good heteroepitaxial reflectors with a crack-free surface morphology were obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347034
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular beam epitaxy of Nd-doped CaF2 and CaSrF2 layers on Si and GaAs substrates (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 499-503 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The incorporation of Nd3+ in CaF2 layers grown on Si and GaAs substrates by molecular beam epitaxy is studied by photoluminescence spectroscopy. The results are in qualitative agreement with those obtained on CaF2:Nd homoepitaxial layers. A lower emission intensity (∼70%) at λ=1.0475 μm is attributed to residual stress and crystalline defects. Concentration quenching of photoluminescence appears at concentrations higher than 3.6 wt % Nd. The use of (Ca,Sr)F2 for lattice matching to GaAs leads to a significant inhomogeneous broadening of Nd3+ emissions due to disorder in the cationic sublattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351880
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  • 4
    Electronic Resource
    Electronic Resource
    Erratum: Raman scattering study of [hhk]-GaAs/[Si or CaF(2)] strained heterostructures [J. Appl. Phys. 76, 2773 (1994)] (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2849-2849 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359612
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  • 5
    Electronic Resource
    Electronic Resource
    Raman scattering study of [hhk]-GaAs/(Si or CaF2) strained heterostructures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2773-2780 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman spectroscopy is used to measure the frequency shift, symmetry, and activity of long-wavelength optical phonons in several GaAs strained epilayers. The results are compared with theoretical evaluations using the elastic compliances, phonon deformation potentials, and Raman tensors. The effect of growth direction ([001], [111], and [112]) and the substrate nature (Si or CaF2) is analyzed. The importance of nonstandard growth directions, [111] or [112], on residual stress and piezoelectric effect is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357542
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  • 6
    Electronic Resource
    Electronic Resource
    1.54 μm wavelength emission of highly Er-doped CaF2 layers grown by molecular-beam epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 270-273 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CaF2:Er layers have been grown by molecular-beam epitaxy on (100)-oriented CaF2 substrates; the Er concentration ranges from 1% to 50% (mole fraction). The 1.54 μm emission observed under excitation around 800 nm was studied by photoluminescence. Up to 35% Er concentration the integrated emission increases monotonously, quenching appearing for higher doping levels. Photoluminescence results are discussed within the framework of previous studies of Er3+ emission in the near-infrared range (830–860 nm) in order to gain insight into the Er centers involved in the 1.54 μm emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357140
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  • 7
    Electronic Resource
    Electronic Resource
    Strain relaxation in [001]- and [111]-GaAs/CaF2 analyzed by Raman spectroscopy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1126-1132 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Study is devoted to a complete characterization of GaAs/CaSrF2/CaF2 heterostructures. Due to the transparency of CaF2 substrate to visible light, Raman spectra have been obtained at both interface and surface sides of the 2 μm GaAs layer. Moreover, penetration depth of light varying with wavelength allows one to perform a tomography of this layer. The crystalline quality at the vicinity of the surface is analyzed through Raman selection rules for both [001] and [111] growth directions. In the latter case, a stress profile has been realized in order to determine its relaxation into the GaAs layer: It occurs in the first 40 nm from the interface. Finally, this methodology is applied to optimize growth conditions in order to obtain stable highly strained systems. By comparison with photoluminescence data, the Raman probe is shown to be very efficient for this purpose. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358975
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of growth temperature and doping concentration on the distribution of the emitting centers in CaF2:Er molecular beam epitaxial layers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2749-2752 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular beam epitaxy of Er-doped CaF2 layers on (100)oriented CaF2 substrates was performed using CaF2 and ErF3 evaporation cells. The effect of growth temperature and Er concentration on the distribution of the different emission centers observed in these epitaxial Er-doped layers was investigated. Photoluminescence analyses were performed in the 830–860 nm wavelength range in which the 4S3/2→4I13/2 transitions of the Er3+ ions take place. The evolution of the relative emission intensity between single and aggregate Er3+ centers as a function of growth temperature shows that the emission from isolated Er3+ ions is favored in a growth temperature range of 500–520 °C. Emission lines from complex Er3+ centers are found to rise relative to those of isolated sites as Er concentration increases. Finally, no quenching of the integrated luminescence intensity occurs in the concentration range investigated, 0.05–6 mol % (0.1–16 wt%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356211
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  • 9
    Electronic Resource
    Electronic Resource
    Er–Yb codoped CaF2 thin films grown by molecular beam epitaxy (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 679-684 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Yb:Er: codoped CaF2 monocrystalline films have been grown by molecular beam epitaxy (MBE) using YbF3, ErF3, and CaF2 evaporation on CaF2 substrates. Luminescence and excitation of luminescence at 25 K are measured in order to investigate the role of Yb3+ codoping and the effect of the growth conditions during the MBE process on the incorporation of active rare-earth species in CaF2. It is found, from a comparison with earlier work on singly doped thin films, that the energies of the levels of Er3+ ions are not modified by the double doping, whereas mixed complex centers are formed. Growth conditions are found to be important controlling factors for the incorporation of Yb3+ as a sensitizer, and, consequently, for the transfer efficiency. From excitation and absorption spectra it is shown that the lowest component of the Er:4I11/2 manifold has an energy higher than that of Yb:2F5/2 and the consequences are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364230
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  • 10
    Electronic Resource
    Electronic Resource
    On the mode of growth of CaF2 and (Ca,Sr)F2 on GaAs and Si(111) substrates (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2076-2078 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The early stages of molecular-beam epitaxy of (Ca,Sr)F2 and CaF2 on GaAs and Si(111) substrates have been studied by means of in situ Auger electron spectrometry and reflection high-energy electron diffraction. The results obtained show (i) that the growth proceeds in all cases via a two-dimensional mechanism that preserves the atomic flatness of the growth front and (ii) that this growth has a nonpseudomorphic character. This behavior is related to the properties of the fluorides involved. The general trends in fluoride-semiconductor heterostructure growth are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342500
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