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  • 1
    Electronic Resource
    Electronic Resource
    Laser heating and photoluminescence in GaAs and AlxGa1−xAs (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2469-2471 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature band-to-band photoluminescence of GaAs and AlGaAs excited by the 514.5 nm line of an argon ion laser beam was used as a probe to measure the temperature at the focused laser spot. A combined study of the dependence of band-gap energy on increasing laser power density and temperature was undertaken. The band-gap variation with temperature has been correlated with laser induced temperature at the focused laser spot as a function of laser power density. The induced temperature is lower than anticipated from the theories for cw laser heating. This disagreement can be explained by the contribution of photoexcited carriers to the thermal conductivity, which is not considered by theories available for laser heating in semiconductors. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112710
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  • 2
    Electronic Resource
    Electronic Resource
    Raman spectroscopic analysis of the free carrier concentration in GaAs oval defects (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3934-3937 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The free carrier concentration at oval defects in silicon-doped GaAs grown by molecular beam epitaxy has been studied on the basis of longitudinal-optical (LO)-phonon plasmon coupled mode frequency through Raman spectroscopy. The carrier concentration at the oval defects was found to be lower as compared to the defect-free regions. The variations of surface depletion width with the concentration calculated from LO phonon intensities was also used to obtain the carrier concentration at the oval defects. Excellent agreement was found between the carrier concentrations obtained from these two methods. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358573
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  • 3
    Electronic Resource
    Electronic Resource
    Structural and electrical characteristics of Pb0.90La0.15TiO3 thin films on different bottom electrodes (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5637-5643 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pb0.90La0.15TiO3 (PLT15) thin films were deposited by the sol-gel method on Pt, Pt/Si, and RuO2 on Si and Pt/Si bottom electrodes. X-ray diffraction, micro-Raman spectroscopy, and atomic force microscopy techniques were used for structural characterization of these films. PLT15 films on different electrodes showed good surface morphology with dense and uniform microstructure. PLT15 films on solution derived RuO2 bottom electrodes show (100) preferred orientation of growth and result in larger crystallites. Films deposited on a Pt bottom electrode show sharp and intense Raman features indicating better crystallinity and insignificant film–electrode interactions. PLT15 film on a Pt bottom electrode exhibited higher dielectric constant (1300 at 100 kHz) and high values of Pm and Pr, 68 and 46 μC/cm2, respectively, compared to other electrodes. Films on a RuO2 bottom electrode showed relatively inferior dielectric and ferroelectric properties. The ac field dependence of dielectric permittivity at subswitching fields was fitted using the Rayleigh law. It was found that ∼22% of the total measured permittivity was due to irreversible domain wall displacement for the films on a Pt electrode. The reversible polarization components estimated from the capacitance–voltage (C–V) and quasistatic hysteresis measurements showed that Prev/Psat at Vmax for the case of Pt/Si (24%), was larger than that of Pt (11%) bottom electrodes. The observed results were correlated with the domain wall pinning at the disturbed film–electrode interface. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1365062
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  • 4
    Electronic Resource
    Electronic Resource
    Micro-Raman scattering and dielectric investigations of phase transition behavior in the BaTiO3–BaZrO3 system (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 8085-8091 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study, the phase transition behavior of the BaTiO3–BaZrO3 system was studied using micro-Raman scattering and dielectric measurement techniques. BaZrxTi1−xO3 ceramics were prepared for x=0.00, 0.05, 0.08, 0.15, 0.20, and 1.00 compositions using a solid-state reaction technique. A single-phase perovskite structure of the ceramics was identified by the x-ray diffraction technique. The basic phase transition temperatures in these compositions were studied in the temperature range of 70–575 K. The tetragonal to cubic transition temperature was found to decrease with increasing Zr content. The orthorhombic to tetragonal transition temperature that increases with an initial increase in Zr content merges with the tetragonal–cubic transition for x≥0.15 compositions. Raman spectra of rhombohedral and orthorhombic phases could not be distinguished. Excellent agreement between the crystallographic transition temperatures obtained by both techniques suggested that Zr substituted octahedra were uniformly distributed in the material without introducing any mechanical stress. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1369399
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  • 5
    Electronic Resource
    Electronic Resource
    Micro-Raman scattering and x-ray diffraction studies of (Ta2O5)1−x(TiO2)x ceramics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 8688-8694 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High dielectric constant (Ta2O5)1−x(TiO2)x ceramics for x=0.00, 0.05, 0.08, and 0.11 were prepared and studied utilizing micro-Raman scattering and x-ray diffraction techniques. The modification in the lowest frequency phonon mode of pure Ta2O5 with increasing TiO2 content in these ceramics was assigned as Ta–Ti vibrations originating from the interaction between TiO6 octahedra and TaOn5-2n or Ta6O12+6 clusters. Raman spectra, in the range −200–900 °C, reveal a softening of this mode with increasing temperature followed by a structural transformation. A triclinic to monoclinic phase (Hmon′) transition was observed at about 300, 360, 450, and 540 °C for x=0.00, 0.05, 0.08, and 0.11, respectively. It was also found that reannealing at 1150 °C for 12 h transforms these ceramics from triclinic to a metastable monoclinic phase Hmon, which was found to be an irreversible process. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373597
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  • 6
    Electronic Resource
    Electronic Resource
    Photoluminescence study of deep levels in Cr-doped ZnSe (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 439-443 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single crystals of intrinsic ZnSe were grown by the seeded physical vapor transport method and the diffusion doping was utilized to incorporate Cr in these crystals. The radiative recombinations in these samples with Cr concentration in the range 1.0–10.2×1019 cm−3 were studied by the steady state photoluminescence technique. It was found that the Cr deep centers inhibit the band-to-band emission in Cr-doped ZnSe. Except in undoped single crystals, no emission corresponding to the band-to-band transition was observed from any of the doped samples. Instead, the higher wavelength emissions associated with Cr deep levels were obtained. This capture of photoexcited carriers by deep centers was verified using different excitation wavelengths. The role of chromium impurities in nonradiative recombination processes was also evidenced from the sharp decreases in the deep level emission intensity with increasing Cr concentration. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369404
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  • 7
    Electronic Resource
    Electronic Resource
    Micro-Raman investigation of stress variations in lead titanate films on sapphire (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 828-834 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the sol–gel method, PbTiO3 films of 21, 64, 128, 210, 310, and 420 nm thicknesses were obtained on (0001) sapphire. Raman scattering and x-ray diffraction techniques were used to study the correlation between the film thickness and the structural changes on these films. The Raman and x-ray intensities in 21 nm film were too weak to reveal any structural information, while all other films showed tetragonal structure. At room temperature, the variation of lowest E(1TO) phonon mode frequency with film thickness was observed due to compressive stresses in the films. The lattice parameters and the degree of a axis orientation values of tetragonal PbTiO3 have been evaluated as a function of film thickness. The changes in lattice parameters thus obtained were used to estimate the stress at each thickness. An excellent agreement was found between the stress values obtained using Raman and x-ray results. An exponential decrease in stress with increasing film thickness was observed because of the structural changes in the lattice. Accordingly, a downshift in the tetragonal–cubic transition temperature with decreasing film thickness has been interpreted using the conventional Landau–Devonshire approach. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370810
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  • 8
    Electronic Resource
    Electronic Resource
    X-ray photoelectron spectroscopy and micro-Raman analysis of conductive RuO2 thin films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2987-2992 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ruthenium oxide (RuO2) was synthesized in thin film and powder forms using the solution chemistry technique. The oxide electrodes on Si substrates were characterized in terms of their structure, composition, stoichiometry, and conductivity. X-ray lattice parameter calculations and micro-Raman analysis revealed the rutile structure in the material. Both films and powders exhibited an unassigned Raman band at about 477 cm−1 in their Raman spectra. Performing peak frequency calculations for B2g and A1g modes of RuO2 using the rigid-ion model, which ruled out the possibility that this band originated from disorder induced symmetry, allowed silent mode. Based on the x-ray photoelectron spectroscopy (XPS) and temperature dependent Raman studies, this band was assigned to hydrated RuO2. XPS characterizations of our samples revealed minute surface contamination of oxygen and chlorine, probably due to the film preparation and high temperature deposition processes. Films with uniform microstructure, low surface roughness, and good electrical properties meet the requirements for serving as the bottom electrode for the ferroelectric capacitor. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1337588
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  • 9
    Electronic Resource
    Electronic Resource
    Micro-Raman and dielectric phase transition studies in antiferroelectric PbZrO3 thin films (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1730-1732 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Antiferroelectric materials are found to be good alternative material compositions for high-charge-storage devices and transducer applications. Lead zirconate (PZ) is a room-temperature antiferroelectric material. The antiferroelectric nature of PZ thin films was studied over a temperature range of 24–300 °C, in terms of Raman scattering, dielectric constant, and polarization. Temperature-dependent dielectric and polarization studies indicated a nonabrupt phase transition. To alleviate the extrinsic effects influencing the phase transition behavior, Raman scattering studies were done on laser-ablated PZ thin films as a function of temperature and clear phase transformations were observed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1356730
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  • 10
    Electronic Resource
    Electronic Resource
    Raman scattering from oval defects in GaAs epilayers (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 488-490 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Micro-Raman investigations have been carried out at various spots in and around oval defects in epitaxially grown 〈100〉 GaAs wafers. Changes in the crystalline orientation have been observed within the oval defect structure as compared to the normal region. However, the crystalline quality of these defects remain equally good. These oval defects also possess a deviation in stoichiometry, corroborating to the conclusions of other studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109982
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