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  • 2000-2004  (10)
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  • 1
    Electronic Resource
    Electronic Resource
    Strain relaxation in AlGaN/GaN superlattices grown on GaN (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2160-2167 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lattice relaxation of strained AlxGa1−xN/GaN superlattices grown on thick GaN buffer layers is investigated using optical microscopy, x-ray diffraction, and photoluminescence spectroscopy. The results are compared to strained bulk AlxGa1−xN layers particularly with regard to the impact of the superlattice period and the Al content. A relaxation process which keeps the coherency between AlxGa1−xN barriers and GaN wells in the superlattice is found and it is attributed to misfit dislocations at the buffer/superlattice interface. Additionally, the AlxGa1−xN barriers relax via crack channels which form beyond a critical Al content and limit the additional strain energy compared to a free-standing superlattice to a maximum value. Cracks relieve tensile plane stress to an extent similar as in bulk layers, i.e., they do not put the GaN wells of the superlattice under additional plane compression. This is explained by misfit dislocations which nucleate at crack faces and glide into the superlattice at the well/barrier interfaces. The onset of cracking is found to shift to higher tensile stresses in the AlxGa1−xN barriers when increasing the superlattice period which is discussed in view of edge cracks being the starting point of crack channels. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1342020
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  • 2
    Electronic Resource
    Electronic Resource
    Strain relaxation in AlGaN under tensile plane stress (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 7029-7036 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Relaxation of tensile strain in AlxGa1−xN layers of different compositions epitaxially grown on GaN/sapphire is investigated. Extended crack channels along 〈2110〉 directions are formed if the aluminum content exceeds a critical value, which decreases with increasing layer thickness. This process is found to limit the average strain energy density to a maximum value of 4 J/m2. By calculating the stress distribution between cracks and the strain energy release rate for crack propagation, the relaxed strain as measured by x-ray diffraction is correlated to the crack density, and the onsets of crack channeling and layer decohesion are fitted to a fracture toughness of 9 J/m2. Moreover, the crack opening at the surface is found to linearly increase with the stress. Annealing of samples above the growth temperature introduces additional tensile stress due to the mismatch in thermal expansion coefficients between the layer and substrate. This stress is shown to relieve not only by the formation of additional cracks but also by the extension of cracks into the GaN layer and a thermal activated change in the defect structure. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1326852
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  • 3
    Electronic Resource
    Electronic Resource
    In as a surfactant for the growth of GaN (0001) by plasma-assisted molecular-beam epitaxy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3425-3427 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of indium on the surface morphology of GaN (0001) grown by plasma-assisted molecular-beam epitaxy (MBE) has been investigated. The rough and grain-like surface under nitrogen-rich growth conditions becomes smoother and similar to surfaces grown under gallium-rich conditions when a sufficiently high indium flux is used. However, the use of indium instead of gallium-rich conditions prevents the formation of gallium droplets on the surface which are associated with voids at their edges. Since indium is not incorporated into GaN for growth temperatures above 700 °C, it can be used as a surfactant in MBE growth of GaN. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1419232
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  • 4
    Electronic Resource
    Electronic Resource
    560-nm-continuous wave laser emission from ZnSe-based laser diodes on GaAs (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2523-2525 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room-temperature continuous wave (cw)-lasing emission at wavelengths around 560 nm was obtained from ZnSe-based laser diodes grown on GaAs substrates. The wavelengths of the devices are most suitable as lightsources for plastic optical fibers. To achieve this emission wavelength, CdZnSSe quantum wells with high Cd content were employed as active region. The growth of such quantum wells requires Se-rich growth conditions. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1411989
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  • 5
    Electronic Resource
    Electronic Resource
    Spatially modified layer properties related to the formation of gallium droplets on GaN(0001) surfaces during plasma-assisted molecular-beam epitaxy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3827-3829 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface morphology and the spatial distribution of defect-related luminescence of GaN(0001) layers grown by plasma-assisted molecular-beam epitaxy under gallium-rich conditions has been investigated. Droplets of liquid gallium form on the surface during growth and lead to distinct spiral hillocks under the droplet. The droplets are surrounded by extended voids which point to an incomplete gallium adlayer on the GaN surface during growth at the droplet boundary. Cathodoluminescence spectra indicate an enhanced intensity in the yellow spectral range for the GaN under the droplets which is attributed to a change in the local density of point defects in the layer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1377629
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  • 6
    Electronic Resource
    Electronic Resource
    The role of high-temperature island coalescence in the development of stresses in GaN films (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1976-1978 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of dislocations and stress in GaN layers grown by metalorganic vapor phase epitaxy on sapphire is investigated with regard to the average grain diameter. The grain diameter was determined by monitoring the high-temperature GaN island coalescence process during growth using reflectometry. It is found that the density of edge threading dislocations decreases and the compressive stress measured after cooling to room temperature increases when the coalescence thickness and the grain diameter increase. The data are consistent with models of development of tensile stress due to island coalescence during growth. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1359780
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  • 7
    Electronic Resource
    Electronic Resource
    Thermal expansion of bulk and homoepitaxial GaN (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1434-1436 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermal behavior of Mg-doped and intentionally undoped bulk crystals and homoepitaxial GaN was investigated in a wide temperature range from 12 to 600 K. With high-resolution x-ray diffraction, both lattice parameters a and c were determined and the thermal expansion coefficients were calculated. Within the experimental accuracy, mean values were extracted for the temperature ranges 12–100, 100–250, and 250–600 K. These values are essential, especially, for the interpretation of measurements of other GaN properties performed at low temperatures. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290491
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  • 8
    Electronic Resource
    Electronic Resource
    Nondestructive detection of stacking faults for optimization of CdSe/ZnSe quantum-dot structures (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3544-3546 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CdSe/ZnSe quantum structures were systematically investigated by high-resolution x-ray diffraction. The samples were grown at different growth temperatures on GaAs(001) substrates by molecular-beam epitaxy. A model is presented enabling the simulation and quantitative analysis of x-ray diffraction profiles influenced by stacking faults. This yields a fast and nondestructive method for the determination of stacking fault densities after calibration by transmission electron microscopy. A steep increase of the stacking fault density above a critical thickness was found. The critical thickness decreases with increasing growth temperature. Above this critical thickness, the amount of incorporated CdSe remains apparently constant. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328760
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  • 9
    Electronic Resource
    Electronic Resource
    X-ray diffraction analysis of the defect structure in epitaxial GaN (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2145-2147 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution x-ray diffraction has been used to analyze the type and density of threading dislocations in (001)-oriented GaN epitaxial layers. For this, (00l) and (hkl) Bragg reflections with h or k nonzero were studied, the latter one measured in skew symmetric diffraction geometry. The defect analysis was applied to a variety of GaN layers grown by molecular-beam epitaxy under very different conditions. The outcome is a fundamental correlation between the densities of edge- and screw-type dislocations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1314877
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  • 10
    Electronic Resource
    Electronic Resource
    Influence of Structural Properties and of Growth Conditions on Exciton Properties in ZnCdSe/ZnSe Quantum Well Structures (2002)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 384-385 (Jan. 2002), p. 63-66 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/05/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.384-385.63.pdf
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