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  • 1
    Electronic Resource
    Electronic Resource
    Lattice relaxation and three-dimensional reflection high-energy electron-diffraction analysis of strained epitaxial Co/Mn superlattices (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2817-2824 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ observations of reflection high-energy electron diffraction (RHEED) are used to study the structure and growth of epitaxial Co/Mn superlattices on hcp (0001) Ru buffer layers. Mn deposited on fcc (111) or hcp (0001) Co presents a singular growth behavior which can be interpreted as an incoherent growth with compressive stresses perpendicular to the surface. Moreover, the Mn structure is found to switch from a sixfold in-plane symmetric 1×1 structure, which probably corresponds to strained fcc γ-Mn, to a sixfold in-plane symmetric (square root of)3×(square root of)3−30° structure with in-plane lattice parameter a=4.69 A(ring). This structural change occurs at a critical thickness of 5–6 monolayers, after the partial relaxation of the Mn in-plane lattice parameter. An analysis of the three-dimensional contribution to the RHEED patterns shows that the (square root of)3×(square root of)3−30° structure is probably identical to the Cu2Mg Laves phase which in turn closely resembles the α-Mn phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357516
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  • 2
    Electronic Resource
    Electronic Resource
    Ferromagnetic resonance determination of fcc→hcp structural change in epitaxial Co/Mn superlattices : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5601-5603 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of epitaxial [Co24 A(ring)MntMn]12 superlattices (3.2 A(ring)≤tMn≤32 A(ring)) was grown on hcp(0001) Ru buffer layers by ultrahigh vacuum e-beam evaporation. Ferromagnetic resonance has shown that for samples with 3.2 A(ring)≤tMn≤12 A(ring), the cobalt layers are predominantly fcc and almost perfectly fcc for the sample having the thinnest Mn thickness [Co24 A(ring)/Mn3.2 A(ring)]12. For samples with greater Mn thickness (tMn(approximately-greater-than)12 A(ring)), the cobalt layers are predominantly hcp with structural defects corresponding either to large inclusions of fcc Co or stacking faults.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355654
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  • 3
    Electronic Resource
    Electronic Resource
    Growth modes and microstructures of ZnO layers deposited by plasma-assisted molecular-beam epitaxy on (0001) sapphire (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5115-5119 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron microscopy and high resolution x-ray diffraction are used to characterize defects in ZnO layers grown by plasma-assisted molecular-beam epitaxy on (0001) sapphire. Two- and three-dimensional types of growth modes are described and the observed mosaic structure is analyzed in each case. It is found that two-dimensional layers exhibit a roughness as low as 6 nm. Their subdomains have small lateral coherence lengths and a mean in-plane misorientation of ±0.4°, leading to an important dislocation density of 1–4×1010 cm−2. On the contrary, it is demonstrated that, through numerous interactions between dislocations, the three-dimensional growth mode leads to a better structural quality with a larger lateral coherence length and a smaller in-plane mosaic spread of ±0.07°. The total dislocation density is consequently reduced by 1 order of magnitude down to 3–5×109 cm−2 and the radical modification of the structure results in a change of the dislocation distribution. Our results thus demonstrate that two-dimensional growth mode and low full width at half maximum for symmetric x-ray diffraction are a not reliable indicator of a good structural quality. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1412572
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  • 4
    Electronic Resource
    Electronic Resource
    Reduction mechanisms for defect densities in GaN using one- or two-step epitaxial lateral overgrowth methods (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4175-4181 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A transmission electron microscopy study of the reduction mechanisms for defect densities in epitaxial lateral overgrown (ELO) GaN films is presented. In the standard one step ELO, the propagation of defects under the mask is blocked, whereas the defects in the window regions thread up to the surface. We propose an alternative two step ELO method. In a first step, dislocations close to the edge of the (0001) top facet bend at 90°, thereby producing a drastic reduction in the density of defects above the window. After the coalescence, induced by lateral growth in a second step, dislocations are mainly observed in the coalescence boundaries. The density of defects is decreased to 2×10−7 cm−2 over the entire surface and areas nearly 5 μm wide with 5×106 cm−2 dislocations between the center of the windows and the coalescence boundaries are obtained. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373048
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular-beam epitaxy of gallium nitride on (0001) sapphire substrates using ammonia (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1379-1383 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ammonia is used for growing undoped GaN layers by gas source molecular-beam epitaxy on c-plane sapphire substrates. The growth mode is layer by layer as shown by the observation of reflection high-energy electron diffraction intensity oscillations. The structural quality is studied by x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Low-temperature photoluminescence (PL) and reflectivity demonstrate intrinsic excitonic emission. Room-temperature PL exhibits a strong band-edge intensity and a weak deep-level emission, the so-called yellow band. Finally, secondary ion mass spectroscopy is carried out to check the residual impurity levels of Si, C, and O. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366840
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  • 6
    Electronic Resource
    Electronic Resource
    In situ growth monitoring of distributed GaN–AlGaN Bragg reflectors by metalorganic vapor phase epitaxy (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 174-176 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of distributed GaN-AlGaN Bragg reflectors (DBR) has been grown on Al2O3(0001) substrates by metalorganic vapor phase epitaxy. The growth of the GaN template as well as of the GaN–AlxGa1−xN quarter-wave stack has been monitored by laser reflectometry. The evolution of the in situ reflectivity as well as DBR reflection spectra are discussed as function of the AlxGa1−xN composition x. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1430859
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  • 7
    Electronic Resource
    Electronic Resource
    Defect characterization in ZnO layers grown by plasma-enhanced molecular-beam epitaxy on (0001) sapphire substrates (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 194-196 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural properties of high-quality (0001)ZnO/Al2O3 films grown by plasma-enhanced molecular-beam epitaxy are investigated by x-ray diffraction and transmission electron microscopy. The only defects encountered are threading dislocations with a density of 1010–4×1010 cm−2. Most numerous dislocations are pure-edge dislocations (Burgers vector of 1/3〈112¯0〉), which accommodate slight in-plane misorientations between subgrains. The oxygen polarity of these films is also established. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1384907
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  • 8
    Electronic Resource
    Electronic Resource
    Stress control in GaN grown on silicon (111) by metalorganic vapor phase epitaxy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3230-3232 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The strain in GaN epitaxial layers grown on silicon (111) substrates by metalorganic vapor phase epitaxy has been investigated. The insertion of AlN/GaN superlattices was found to decrease the stress sufficiently for avoiding crack formation in an overgrown thick (2.5 μm) GaN layer. X-ray diffraction and photoluminescence measurements are used to determine the effect of these AlN/GaN superlattices on the strain in the subsequent GaN layers. A reduction of threading dislocation density is also observed by transmission electron microscopy and atomic force microscopy when such superlattices are used. Strong band edge photoluminescence of GaN on Si(111) was observed with a full width at half maximum of the bound exciton line as low as 6 meV at 10 K. The 500 arcsec linewidth on the (002) x-ray rocking curve also attests the high crystalline quality of GaN on Si (111), when using these AlN/GaN superlattices. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415043
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  • 9
    Electronic Resource
    Electronic Resource
    Phase separation in metalorganic vapor-phase epitaxy AlxGa(1−x)N films deposited on 6H–SiC (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 4310-4312 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure of AlxGa(1−x)N films deposited on 6H–SiC substrates by metalorganic vapor-phase epitaxy is studied by transmission electron microscopy and energy-dispersive x-ray analysis. It is shown that in the first step of the growth (three-dimensional), the deposit is constituted of a thin Al-rich AlGaN wetting layer covering the substrate surmounted by pure GaN islands. In a second step, a homogeneous AlxGa(1−x)N film, with nominal Al concentration, is deposited and smoothing is observed. The results of the high-resolution transmission electron microscopy about the strain state of the different parts of the deposit indicate that the driving force for the phase separation phenomena is the decrease of the interfacial energy due to the low mismatch between Al-rich AlGaN and 6H–SiC (1% for pure AlN). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1336166
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  • 10
    Electronic Resource
    Electronic Resource
    Electron energy-loss spectroscopy characterization of pyramidal defects in metalorganic vapor-phase epitaxy Mg-doped GaN thin films (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2115-2117 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the present letter, Mg-doped GaN thin films grown by metalorganic vapor-phase epitaxy were studied using parallel electron energy-loss spectroscopy in a transmission electron microscope. A microstructural characterization of such thin films showed the presence of pyramidal defects (PDs) with a density of about 1018 cm−3. Comparison of energy-loss spectra recorded outside a PD and from the PD showed a significant change in the energy-loss near-edge structure strongly reflecting the presence of inclusions (Mg-based), the electronic properties of which differ from those of GaN. Considering, however, their relatively high density (∼1018 cm−3), one can expect that the optical properties of such inclusions may interfere with those of GaN and, therefore, be at the origin of the frequently obtained blue emission at 2.8–2.9 eV in heavily doped samples. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1313811
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