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  • 1
    Electronic Resource
    Electronic Resource
    Study of structural changes in amorphous germanium–nitrogen alloys by optical techniques (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 433-438 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of amorphous germanium–nitrogen (a-GeN) alloys prepared by the rf sputtering deposition technique have been studied by Raman scattering spectroscopy. The nitrogen content of the samples varies between zero and ≈3×1022 atoms cm−3, as determined from nuclear reaction analysis data. Modifications of the structural characteristics of the Ge–N alloys, probed through their phonon density, were investigated as a function of the nitrogen concentration. In addition to an increase of the network's topological disorder, nitrogen is responsible, at relatively high concentrations, for a structural transition in the a-Ge host. The optical and electronic characterization of the samples confirm these changes which are highly dependent on the nitrogen concentration. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360849
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  • 2
    Electronic Resource
    Electronic Resource
    Laser interference structuring of a-Ge films on GaAs (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 2916-2920 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the laser interference crystallization (LIC) of amorphous germanium films on (100)-oriented GaAs substrates using nanosecond laser pulses. We demonstrate that LIC can produce periodic arrays of epitaxially crystallized Ge lines on GaAs with submicrometer widths. The gratings display a surface undulation with faceted surfaces, which depends on laser fluency. The undulation is attributed to the lateral solidification process induced by the temperature gradients created during the LIC process. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448674
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  • 3
    Electronic Resource
    Electronic Resource
    Epitaxial pulsed laser crystallization of amorphous germanium on GaAs (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 2575-2581 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the crystallization of amorphous germanium films on GaAs crystals using nanosecond laser pulses. The structure and composition of the crystallized layers is dominated by nonequilibrium effects induced by the fast cooling process following laser irradiation. Perfect epitaxial films are obtained for fluencies that completely melt the Ge film, but not the substrate. For higher fluencies, partial melting of the substrate leads to the formation of a (GaAs)1−xGe2x epitaxial alloy with a graded composition profile at the interface with the substrate. Since Ge and GaAs are thermodynamically immiscible in the solid phase, the formation of the alloy is attributed to the suppression of phase separation during the fast cooling process. Lower laser fluencies lead to polycrystalline layers with a patterned surface structure. The latter is attributed to the freeze-in of instabilities in the melt during the fast solidification process. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1390312
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of superlattices based on amorphous silicon (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 556-560 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have characterized the structure of superlattices (SL's) based on amorphous silicon by optical interference microscopy and secondary electron micrographs. Differences in the etch rate of a-Si:H and a-SiNx:H in CP6 create a series of terraces and steps in a-Si:H/a-SiNx:H superlattices that show up clearly in interference contrast micrographs and allow an assessment of the quality of the SL. Secondary electron microscopy images of doping superlattices (npnp or nini) of a-Si:H reveal after plasma etching the layered nature of the samples. The necessary contrast is provided by differences in the etch rate of the two interfaces (i.e., n→p vs p→n). Evidence for structural differences of the interfaces of nini multilayers stems from secondary ion mass spectrometry and 15N depth profiles of hydrogen that show an extra amount of H of the order of 1015 cm−2 only at that interface where intrinsic a-Si:H is growing on top of the n-type material. We explain these results in terms of a growth model which entails a hydrogen enrichment over its bulk concentration that is not limited to the surface but extends into a subsurface region during the film deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338258
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  • 5
    Electronic Resource
    Electronic Resource
    Efficient energy upconversion emission in Tm3+/Yb3+-codoped TeO2-based optical glasses excited at 1.064 μm (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6550-6552 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Efficient energy upconversion of cw radiation at 1.064 μm into blue, red, and near infrared emission in Tm3+-doped Yb3+-sensitized 60TeO2-10GeO2-10K2O-10Li2O-10Nb2O5 glasses is reported. Intense blue upconversion luminescence at 485 nm corresponding to the Tm3+ 1G4→3H6 transition with a measured absolute power of 0.1 μW for 800 mW excitation power at room temperature is observed. The experimental results also revealed a sevenfold enhancement in the upconversion efficiency when the sample was heated from room temperature to 235 °C yielding 0.7 μW of blue absolute fluorescence power for 800 mW pump power. High brightness emission around 800 nm (3F4→3H6) in addition to a less intense 655 nm (1G4→3H4 and 3F2,3→3H6) fluorescence is also recorded. The energy upconversion excitation mechanism for thulium emitting levels is assigned to multiphonon-assisted anti-Stokes excitation of the ytterbium-sensitizer followed by multiphonon-assisted sequential energy-transfer processes. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413489
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  • 6
    Electronic Resource
    Electronic Resource
    Structure of interfaces in a-SiB: H/a-SiNx@B: H superlattices (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 778-785 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present experimental results on the atomic structure of the interfaces between a-Si:H and a-SiNx:H layers obtained by analyzing the intensity of the Raman lines from zone-folded acoustic phonons and of the peaks of x-ray diffraction at grazing angles. We determine the width of these interfaces and their stability under thermal annealing in temperatures below the crystallization temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347364
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  • 7
    Electronic Resource
    Electronic Resource
    Resonance Raman spectra of the heptanuclear hexakis(pentaammineruthenium)tris(bipyrazine)ruthenium(14+) complex. Excitation profiles for three overlapping metal-to-ligand charge-transfer bands (1988)
    s.l. : American Chemical Society
    Inorganic chemistry 27 (1988), S. 3850-3853 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00294a033
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  • 8
    Electronic Resource
    Electronic Resource
    Blue cooperative luminescence in Yb3+-doped tellurite glasses excited at 1.064 μm (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 6772-6776 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Blue luminescence emission around 480 nm through cooperative upconversion from pairs of Yb3+ ions implanted into 60TeO2–10GeO2–10K2O–10Li2O–10Nb2O5 tellurite glasses and excited by a cw laser at 1.064 μm is demonstrated. Cooperative luminescence emission enhancement owing to the temperature dependent multiphonon-assisted anti-Stokes excitation process of the ytterbium ions is also observed. The experimental results revealed a fourfold enhancement in the cooperative luminescence emission when the sample was heated in the temperature range of 20 °C–260 °C. The thermally induced enhancement is assigned to the effective absorption cross-section for the ytterbium ions which is an increasing function of the medium temperature. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1463397
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  • 9
    Electronic Resource
    Electronic Resource
    Short-pulse laser-induced crystallization of intrinsic and hydrogenated amorphous germanium thin films (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 5159-5166 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the laser crystallization of intrinsic (a-Ge) and hydrogenated (a-Ge:H) amorphous germanium thin films using short, i.e., ns range, laser pulses. The influence of hydrogen on the phase transitions was investigated by monitoring the reflectance of the sample during laser irradiation. We determined the thresholds for melting (36 mJ/cm2) and for surface damage (66 mJ/cm2) of the a-Ge film. In a-Ge:H, hydrogen effuses on a short time scale (10 ns) upon laser irradiation. The effusion leads to the formation of a lifted-off (100 nm thick) crystalline Ge membrane, leaving behind a rough and incompletely crystallized surface. In a-Ge, on the other hand, no surface disruption is observed. The Raman spectra of hydrogenated samples are dominated by stress effects, while those corresponding to non-hydrogenated samples are dominated by crystallite size distribution effects. We also conclude that laser-induced annealing, carried out by applying several pulses with increasing intensity, can be used as a tool for the crystallization of a-Ge:H samples without hydrogen-induced surface damage. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366320
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  • 10
    Electronic Resource
    Electronic Resource
    Photoluminescence modulation by high-frequency lateral electric fields in quantum wells (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1559-1561 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the modulation of the excitonic photoluminescence (PL) of GaAs quantum wells by high-frequency (frf) lateral electric fields. Under these fields, the PL becomes modulated in the form of pulses with repetition frequency of 2 frf. The periodic PL modulation is attributed to the time-dependent ionization of photogenerated excitons under the lateral electric field. The exciton ionization mechanism is proposed to be the impact ionization with electrons accelerated by the electric fields with a threshold field for ionization of about 15 V/cm. The different transport properties of electrons and holes are found to play a role in the exciton ionization process. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355292
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