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  • Articles  (26)
  • American Institute of Physics (AIP)  (16)
  • Springer  (10)
  • 2000-2004  (26)
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  • Articles  (26)
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1104-1107 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the effect of strain-induced indium clustering on the emission properties of InGaN/GaN multiple quantum wells grown with high indium composition by metalorganic chemical vapor deposition. Indium clustering confirmed by high-resolution transmission electron microscopy results in the redshift of the emission peak and the increase of the integrated photoluminescence (PL) intensity. We found that strong carrier localization in indium clustering induces the increases of the activation energy of PL integrated intensity, the temperature independence of PL decay profiles, and the intensity fluctuation of the cathodoluminescence images. All these observations suggest structurally and optically that the improved emission properties in the InGaN/GaN multiple quantum well with high indium composition are associated with the localized states in the strain-induced indium cluster. © 2002 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1166-1170 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Influence of strain relaxation on structural and optical properties of the InGaN/GaN multiple quantum wells (MQWs) with high indium composition grown by metalorganic chemical vapor deposition was investigated. From photoluminescence and transmission electron microscopy (TEM), we found that within the MQWs, the formation of misfit dislocation affects the degradation of optical properties more than the formation of stacking faults. For the MQWs with indium composition above the critical indium composition on the formation of misfit dislocation, the position of the main emission peak is significantly affected by the increase of quantum well numbers compared to samples with indium composition below the critical indium composition. The origins of redshift by the increase of quantum well numbers is believed to be caused by the increase of indium segregation in the MQWs using high-resolution TEM and energy dispersive x-ray spectroscopy. © 2002 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4027-4031 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron microscopy (TEM) and selected area electron diffraction pattern (SADP) measurements were carried out to investigate the ordered structures near ZnTe/GaAs heterointerfaces, and Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) measurements were performed to determine the compositions of the ZnTe/GaAs interfacial layer. The SADP showed two sets of {〈fraction SHAPE="CASE"〉12 〈fraction SHAPE="CASE"〉12 〈fraction SHAPE="CASE"〉12} extra spots with symmetrical intensity, and the corresponding high-resolution TEM image showed doublet periodicity in contrast of the {111} lattice planes. The results of the SADP and the high-resolution TEM measurements showed that a CuPt-type ordered (Cd, Zn)Te structure was observed near the ZnTe/GaAs heterointerface, and the AES and SIMS results showed that the ordered structure was formed due to the diffusion of Cd atoms into the ZnTe layer. Two variants, one for each direction of the doublet periodicity on the {111} lattice, were observed in the ordering, and each variant had its own domain structure with a similar probability. The formation of the CuPt-type ordered structure near the ZnTe/GaAs heterointerface originated from both the existence of the Cd residual impurities during the initial growth stage of the ZnTe epilayer and the strain relaxation of the ZnTe epilayer. These results can help to improve the understanding of the microstructural properties of the ZnTe/GaAs heterointerface. © 2001 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6297-6301 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of Permalloy films, of various shapes such as a square, a rectangle, a circle, and a rhombus, was made. The sample length to width ratio L/w varied from 1 (i.e., square) to 29 (i.e., rectangle). We studied how the planar Hall effect (PHE) signal was affected by adding a transverse field Hy along the easy-axis direction of the sample. It was found that in a certain range of Hy, the PHE sensitivity S might become inoperative, i.e., S changed linearly as a function of Hy from −Smax to +Smax (or vice versa), where Smax was the maximum sensitivity. This phenomenon is explained by considering the Zeeman-energy and the single-domain-rotation effects. In particular, for the square sample, the following data exist: (1) Smax is as high as 310 Ω/T at the film thickness t=500 Å, and (2) the inoperative range for Hy is the narrowest among all the samples. From this study, we conclude that the field of the Earth He—as long as its horizontal component is larger than 0.25 Oe—can be employed to stabilize the magnetic structure of a Permalloy element and to achieve the best PHE performance with Smax. © 2001 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6223-6227 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report thermopower measurements for the nickel titanium shape memory alloy Ni0.507Ti0.493. Our measurements reveal abrupt changes in the temperature dependence of thermopower, which correlate well with the structural phase transition between the austenitic and martensitic phases. These transition effects in thermopower are more clearly defined than in the resistivity, which is also reported. In the martensitic phase, thermopower exhibits standard metallic diffusion behavior with a nonlinearity, which is consistent with either a small peak in the density of states just below the Fermi level, as calculated by Kulkova, Egorushkin, and Kalchikhin [Solid State Commun. 77, 667 (1991)], or else electron–phonon mass enhancement. For thermally or mechanically treated samples, the magnitude of the transition effects in thermopower are reduced. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5195-5199 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructural and the optical properties of InAs/GaAs quantum-dot (QD) arrays inserted into undoped GaAs barriers embedded in an AlxGa1−xAs/GaAs were investigated by using transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images and the selected-area electron diffraction patterns showed that vertically stacked InAs QD self-assembled arrays were embedded in the GaAs barriers. The temperature-dependent PL spectra showed that the peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band of the InAs QDs shifted to lower energy with increasing temperature. The PL intensity of the InAs dots was significantly enhanced by the modulation-doped AlxGa1−xAs/GaAs heterostructure, and the thermal activation energy of the InAs dots was decreased by the addition of the modulation-doped AlxGa1−xAs/GaAs heterostructure. The present results can help to improve the understanding of the microstructural and the optical properties in InAs QD arrays inserted into GaAs barriers embedded in a modulation-doped AlxGa1−xAs/GaAs heterostructure. © 2002 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 2397-2404 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The minority carrier lifetime in boron-doped oxygen-contaminated Czochralski (Cz) silicon is strongly reduced under illumination or carrier injection. This process can be fully reversed by a 200 °C anneal step. In several recent studies it was shown that boron and oxygen are the major components of the underlying metastable Cz-specific defect. The energy level of the defect in its active state A was determined to be around midgap [Schmidt et al., J. Appl. Phys. 86, 3175 (1999)] while the energy level of the defect in its passive state P is very shallow. The Cz-specific defect in its passive state can be identified with the shallow thermal donor. The kinetics of the excess carrier-induced transformation from state P to state A can be described using recombination-enhanced defect reaction theory. On the basis of these experimental facts different solutions for the reduction or elimination of the metastable defect are suggested. Two promising solutions are discussed in more detail: the use of gallium-doped Cz silicon and the introduction of high-temperature anneals into the process sequence. Gallium-doped Cz silicon shows no degradation and excellent lifetimes over a wide resistivity range, although the concentration of interstitial oxygen is in the same range as in standard Cz silicon. Stable solar cell efficiencies comparable to FZ silicon have been achieved. If standard boron-doped Cz silicon is used, the defect concentration can be reduced permanently by a high-temperature anneal using conventional tube or rapid thermal processing. This leads to an improvement of the carrier lifetime by a factor of 2–3. Nevertheless, it is always necessary to use an optimized set of process parameters because otherwise the lifetime of all oxygen-contaminated materials (including gallium-doped Cz silicon) is severely reduced © 2001 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1370-1372 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pit formation in III-nitride heterostructures such as InGaN/GaN and AlGaN/GaN grown by metalorganic chemical vapor deposition was characterized by transmission electron microscopy. The pit formation related with V defects has been reported in the InGaN/GaN multiple quantum well with high In composition [Appl. Phys. Lett. 79, 215 (2001)]. In this letter, we found that the mechanism of pit formation strongly depends on the indium and aluminum compositions in InxGa1-xN and AlxGa1-xN layers, respectively. By increasing the indium composition, the origin of pits is changed from the vertex of threading dislocations to the stacking mismatch boundaries induced by stacking faults and the three-dimensional island growth at the initial stage due to the large lattice mismatch. By increasing the aluminum composition, the origin of the pits also varied from the surface undulation due to the elastic misfit strain to the vertex of threading dislocations. In addition, several inversion domains observed in III nitrides result in pit formation in the surface of films. © 2002 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 247-249 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InxGa1−xN alloys were directly grown on sapphire substrate with a GaN nucleation layer. The degree of phase separation in the InGaN layer on sapphire substrate is maximized at higher growth temperature than for an InGaN layer grown on a thick GaN layer. For high indium composition, a superlattice-like stacking fault in the InxGa1−xN grown on sapphire substrate was detected by the selected area diffraction pattern and high-resolution transmission electron microscopy. The superlattice-like arrangement of stacking faults leads to the formation of split spots and the distance of split spots corresponds to the distance between stacking faults. © 2000 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 215-217 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: V-defect formation of the InxGa1−xN/GaN multiple quantum wells (MQWs) grown on GaN layers with different threading dislocation (TD) densities was investigated. From cross-sectional transmission electron microscopy, we found that all V defects are not always connected with TDs at their bottom. By increasing the indium composition in the InxGa1−xN well layer or decreasing the TD density of the thick GaN layer, many V defects are generated from the stacking mismatch boundaries induced by stacking faults which are formed within the MQW due to the strain relaxation. Also, TD density in the thick GaN layer affects not only the origin of V-defect formation but also the critical indium composition of the InxGa1−xN well on the formation of V defects. © 2001 American Institute of Physics.
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