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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Nd3+ concentration on the emission spectra of CaF2:Nd layers grown by molecular-beam epitaxy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4485-4489 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nd3+-doped CaF2 monocrystalline films have been grown by molecular-beam epitaxy using CaF2 and NdF3 evaporation on CaF2 (100) substrates. Auger electron spectrometry and high-energy electron diffraction have been used as in situ techniques to characterize the grown layers. No degradation of crystallinity was observed even for the highest levels of doping considered. The effect of Nd3+ concentration is studied by means of the photoluminescence signal of Nd3+ ions. The results can be compared favorably with those of bulk CaF2:Nd crystals. For a given Nd3+ concentration a lower quantity of Nd3+ aggregate centers is observed. Nd3+ ions can, therefore, be efficiently incorporated in isolated Nd3+-F− centers up to concentrations of 3.7 wt % Nd3+ without emission quenching of the associated line at 1.0457 μm. The results are related to the thermodynamic conditions imposed by the molecular-beam epitaxy technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349082
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Tin diffusion and segregation in GaAs processed with a pulsed ruby laser (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3832-3837 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tin-diffused GaAs layer samples, with mean concentrations larger than 1019 cm−3, were obtained by irradiating with a ruby laser GaAs substrates covered with thin tin layers. Mobilities between 100 and 200 cm2/V s were obtained. Both carrier concentration and mobility decrease with increasing energy density. Strong segregation effects were observed in the samples processed with large energy densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346267
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Polar phonon-intersubband plasmon coupling in Si delta-doped GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1072-1078 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The present work is devoted to Raman scattering by coupled phonon-intersubband plasmon excitations in Si δ-doped GaAs. The signature of the coupled modes is pointed out by means of difference Raman scattering, and their symmetry determined according to the selection rules. A good agreement is found between the experimental spectra and those calculated in the frame of the dielectric response theory. Raman depth profiling measurements have been performed for two locations of the Si-doped sheet with respect to the sample surface. These results give evidence for electron localization in the vicinity of the doped sheet and allow the spatial extent of the electron gas to be estimated. The change undergone by the Raman signal of the coupled phonon-plasmon system is studied as a function of doping level, and the ion spreading effects are discussed. The measurements performed in a wide range of temperature are also presented and analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354954
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Raman study of longitudinal optical phonon-plasmon coupling and disorder effects in heavily Be-doped GaAs (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4064-4070 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman spectroscopy measurements have been performed on GaAs:Be samples with high crystalline quality and exceptional heavy doping level ranging from 1019 to 1.4×1021 cm−3. The recorded spectra show a structure we assigned to a coupled LO phonon-damped plasmon mode. A theoretical expression for the Raman scattering rate by this mode has been derived from a dielectric model and compared to the experimental data. Using a fitting procedure the doping level of the samples has been estimated in agreement with Hall measurements. Moreover, the study of the Raman intensity evolution of both unscreened-LO and coupled phonon-plasmon structures, provided a convenient and rapid method to determine the activated carrier density in p-doped polar semiconductors. Disorder effects due to the dopant impurities have been also observed and analyzed using a spatial correlation model description.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348957
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  • 8
    Electronic Resource
    Electronic Resource
    Hetero- and homoepitaxial Nd3+-doped LaF3 thin films grown by molecular beam epitaxy: A spectroscopic study (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3699-3704 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hetero- and homoepitaxial Nd3+-doped LaF3 thin films have been grown by molecular beam epitaxy. Two different orientations of CaF2 substrates, (111) and (110), have been used for the heteroepitaxial structures. High-resolution emission and excitation spectra as well as the decay time of the emission have been measured. The spectroscopic measurements demonstrate that one Nd3+ site is present in the LaF3 layers grown on CaF2(111) substrates but two slightly different Nd3+ centers are resolved in the films on CaF2(110) substrates. One Nd3+ site has been found in the homoepitaxial sample. Slight differences are observed between the centers found in the LaF3 layers and the one observed in the Nd3+-doped LaF3 bulk crystal. For the homoepitaxial layer, the linewidths are similar to those of the bulk crystals, whereas for the heteroepitaxial layers, a broadening is observed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371281
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  • 9
    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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  • 10
    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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