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  • 1
    Electronic Resource
    Electronic Resource
    Microstructure of columnar crystallites in Ni80Fe20/Cu magnetic multilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2835-2839 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used electron microscopy to investigate the microstructure of Ni80Fe20/Cu magnetic multilayers which were synthesized by dc magnetron sputtering. Columnar structure was found in the specimen with and without giant magnetoresistance (GMR). All the columnar crystallites (CCs) originate from the Fe buffer layer on silicon wafer or glass substrate and penetrate though all the multilayers up to the surface of the film. The lateral size of the CCs ranges from 10 to 30 nm. Cross-sectional high-resolution electron microscopy study shows that the CCs are single-crystal-like with fcc structure resulting from the epitaxial growth of NiFe and Cu sublayers. Electron diffraction contrast imaging and electron energy filtered elemental mapping confirmed that multilayer nature is maintained throughout the entire NiFe/Cu film. Grain boundaries between CCs can be the most likely place where NiFe or Cu bridging will occur. Columnar structure was also found in a Ta/NiFe/Cu/NiFe/FeMn/Ta spin valve film. The possible influence of the columnar crystalline structure on the GMR related problems is discussed. The microstructure results revealed in this article provide useful information for the GMR property investigation of NiFe/Cu based metallic multilayers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372265
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  • 2
    Electronic Resource
    Electronic Resource
    Optical investigations of GaInNAs/GaAs multi-quantum wells with low nitrogen content (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 1380-1385 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical properties of GaInNAs/GaAs multi-quantum wells were investigated by photoluminescence excitation (PLE) spectroscopy, as well as by photoluminescence (PL), under various excitation intensities and at various temperatures. The PLE spectra demonstrated pronounced excitonic features and the corresponding transitions were identified. At low temperatures the PL spectra were sensitive to the excitation intensity. Under fixed excitation intensity, both the peak energy and the linewidth of photoluminescence showed anomalous temperature dependence, specifically an S-shaped temperature dependence of the peak energy and a N-shaped temperature dependence of linewidth in the PL spectra. The observed results are explained consistently in terms of the exciton localization effect due to the local fluctuations of nitrogen concentration. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1489716
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  • 3
    Electronic Resource
    Electronic Resource
    Enhancement of exciton binding energies in ZnO/ZnMgO multiquantum wells (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1993-1997 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of confinement on the exciton binding energies has been systematically investigated for two series of ZnO/ZnMgO multiquantum wells with various well widths and barrier heights. The exciton binding energies were extracted from the energy difference between the stimulated emission band induced by inelastic exciton–exciton scattering and the free exciton absorption band. The binding energies of excitons are found to be sensitively dependent on the well widths. The experimental results of the well width dependence of binding energies are in good agreement with Coli and Bajaj's theoretical calculations for these structures [G. Coli and K. K. Bajaj, Appl. Phys. Lett. 78, 2861 (2001)]. The remarkable reduction in coupling strength between excitons and longitudinal optical phonons is closely correlated with the enhancement of the exciton binding energy, indicating that the stability of excitons is greatly increased by the enhancement of exciton binding energy in quantum wells. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1445280
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature dependence of excitonic absorption spectra in ZnO/Zn0.88Mg0.12O multiquantum wells grown on lattice-matched substrates (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2464-2466 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The excitonic properties of high-quality ZnO/Zn0.88Mg0.12O multiquantum wells grown by laser-molecular-beam epitaxy were investigated using temperature-dependent optical absorption spectra from 5 K to room temperature. The strength of exciton-longitudinal-optical (LO) -phonon coupling was deduced from the temperature dependence of the linewidth of the fundamental excitonic peak. Effective reduction of the exciton-LO-phonon coupling with decreasing the well width was observed, which is consistent with the confinement-induced enhancement of the exciton binding energy. The thermal shift of the lowest excitonic energy is independent of well width, indicating that the strain effect is negligible for this material. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1367300
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  • 5
    Electronic Resource
    Electronic Resource
    Stimulated emission induced by exciton–exciton scattering in ZnO/ZnMgO multiquantum wells up to room temperature (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 4250-4252 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism of ultraviolet stimulated emission was investigated in ZnO/ZnMgO multiquantum wells. Stimulated emission induced by exciton–exciton scattering occurred throughout a range of temperatures from 5 K to room temperature. At temperatures higher than 160 K, stimulated emission due to electron-hole plasma recombination was also observed with a higher excitation threshold than that of exciton–exciton scattering. The exciton binding energies of multiquantum wells were larger than that of bulk ZnO and increased with a decrease in the well widths. This enhancement of exciton binding energy is due to the quantum-confinement effect and is favorable for the stability of exciton states. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333687
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  • 6
    Electronic Resource
    Electronic Resource
    Two-photon readout of three-dimensional memory in silica (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 13-15 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the readout of three-dimensional (3D) optical memory in silica by detecting the photoluminescence (PL) of the bits (voxels). A broad defect-related PL band at 400–700 nm was excited by two-photon absorption of femtosecond (pulse duration of 120 fs) illumination at 795 nm. We employed a simple reflection-type scanning readout without the use of a confocal detection scheme to read 3D memory by recording the PL of the bits (the same objective lens was used for the excitation and the collection of the PL). Bit plane separation as small as 3 μm was resolved without cross talk, when the theoretical limit of the axial resolution evaluated as a full-width at half maximum measure of a bit size was 1.4 μm at the fabrication conditions employed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126861
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  • 7
    Electronic Resource
    Electronic Resource
    Biexciton emission from ZnO/Zn0.74Mg0.26O multiquantum wells (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3385-3387 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Luminescence due to the radiative recombination of localized biexcitons has been observed at low temperature (5 K) in ZnO/Zn0.74Mg0.26O multiquantum wells grown by laser-molecular-beam epilaxy on a lattice-matched ScAlMgO4 substrate (0001). The emission components due to the recombination of localized excitons and biexcitons and due to the exciton–exciton scattering were verified by examining their relative energy positions and intensity dependence on excitation power density. The excitation threshold for biexciton emission was significantly lower than that for exciton–exciton scattering. The binding energy of biexcitons in multi-quantum wells is largely enhanced by quantum confinement effect. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1375830
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of buffer layer and growth temperature on the properties of an undoped GaN layer grown on sapphire substrate by metalorganic chemical vapor deposition (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2220-2222 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of low-temperature buffer layer thickness on the electrical properties of GaN film is investigated, and the surface morphology is also examined by atomic force microscopy. A best surface morphology does not show best electrical properties, which could be attributed to the usual growth mechanism for GaN film on sapphire substrate. The influence of the growth temperature for the final GaN layer is also investigated. When the growth temperature increases to 1100 °C, the mobility is greatly enhanced to 600 cm2/V s with a background carrier density of 3.3×1016/cm3 at room temperature. The emission energy of the near band gap exciton at a low temperature shows a blueshift with increasing growth temperature due to an enhanced thermal stress. The calculation based on a thermal stress model agrees very well with the photoluminescence measurement. This result could partly explain the reason that the previously published values for the near band gap exciton emission energy are scattered. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126302
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  • 9
    Electronic Resource
    Electronic Resource
    Temperature dependence of near ultraviolet photoluminescence in ZnO/(Mg, Zn)O multiple quantum wells (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1979-1981 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on temperature dependence of excitonic photoluminescence (PL) from ZnO/(Mg, Zn)O multiple quantum wells (MQWs). Two kinds of MQWs having different barrier heights grown by laser molecular-beam epitaxy showed significantly different temperature dependences of PL spectra; in ZnO/Mg0.27Zn0.73O MQWs, the PL peak energy at 50–200 K was a monotonically increasing function of temperature, which was opposite to that ascribed by band gap shrinkage. Moreover, spectra taken at 95–200 K encompassed two peaks, both of which originated from recombination of localized excitons. The temperature-induced shift (redshift-blueshift-peak duplication-redshift) at 5–300 K is caused by a change in the exciton dynamics with increasing temperature due to inhomogeneity and the exciton localization effect. On the other hand, the corresponding dependence in ZnO/Mg0.12Zn0.88O MQWs (lower barrier height) was similar to that in bulk II–VI semiconductors. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357451
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  • 10
    Electronic Resource
    Electronic Resource
    Room-temperature luminescence of excitons in ZnO/(Mg, Zn)O multiple quantum wells on lattice-matched substrates (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 975-977 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the optical properties of ZnO/(Mg, Zn)O multiple quantum wells (MQWs) on lattice-matched ScAlMgO4 substrates fabricated by laser molecular-beam epitaxy. As the well layer thickness decreased down to 7 Å, the photoluminescence (PL) and absorption peaks showed a systematic blueshift, consistent with the quantum-size effect. Moreover, a bright PL of free excitons could be observed even at room temperature. As a result, the PL could be tuned in the energy range of 3.3–3.6 eV by choosing the appropriate barrier height and well layer thickness. The widest tunability on the room-temperature luminescence of the excitons could be attained on the basis of the ZnO quantum structure. These favorable properties could not be attained in the MQWs on lattice-mismatched sapphire substrates. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289066
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