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  • 1
    Electronic Resource
    Electronic Resource
    Dislocation imaging using transmission ion channeling (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2640-2653 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interface dislocations present in a Si0.85Ge0.15/Si sample have been imaged using the channeling scanning transmission ion microscopy (CSTIM) method with a 2 MeV proton beam 200 nm across. Groups of parallel dislocations gave dark bands of contrast down to ∼1.5 μm across, the contrast arising from dechanneling of the beam by the bent lattice planes. Tilting of the sample caused the band contrast to change and gave quantitative data concerning the local bending of the lattice planes. A low-angle boundary model was developed to describe the effect of the groups of dislocations on the channeling contrast. Channeling and topography contrast were obtained from mesa structures present on the sample. Improvements in the sensitivity of the CSTIM method are discussed. The dislocations in the sample were initially characterized by transmission electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353081
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of Si doping on strain, cracking, and microstructure in GaN thin films grown by metalorganic chemical vapor deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7745-7752 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of Si doping on the strain and microstructure in GaN films grown on sapphire by metalorganic chemical vapor deposition was investigated. Strain was measured quantitatively by x-ray diffraction, Raman spectroscopy, and wafer curvature techniques. It was found that for a Si concentration of 2×1019 cm−3, the threshold for crack formation during film growth was 2.0 μm. Transmission electron microscopy and micro-Raman observations showed that cracking proceeds without plastic deformation (i.e., dislocation motion), and occurs catastrophically along the low energy {11(underbar)00} cleavage plane of GaN. First-principles calculations were used to show that the substitution of Si for Ga in the lattice causes only negligible changes in the lattice constant. The cracking is attributed to tensile stress in the film present at the growth temperature. The increase in tensile stress caused by Si doping is discussed in terms of a crystallite coalescence model. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373529
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  • 3
    Electronic Resource
    Electronic Resource
    The use of graded InGaAs layers and patterned substrates to remove threading dislocations from GaAs on Si (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2697-2702 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated threading dislocation (TD) removal from GaAs films on Si by introduction of additional InGaAs graded strain layers in combination with growth on patterned substrates. The substrate patterns consisted of mesas with 10–34 μm widths. The mesa sidewalls were either overhanging (concave), leading to free sidewalls for the film on the mesas, or outward sloping (convex) sidewalls with {111} orientation. The dislocation structure was studied using transmission electron microscopy. It was found that the graded strained layers led to a reduction of dislocation density by a factor of ∼5 in films grown both on mesas with concave sidewalls and on unpatterned substrates. This reduction was due to dislocation reactions leading to annihilation of TDs. For films with graded strained layers on mesas with convex sidewalls, an additional factor of ∼3 reduction in TD density was observed in the part of the film that was grown on top of the mesas. In this case all mobile TDs (TDs associated with 60° misfit dislocations, i.e., TDs that could glide to relieve misfit stress) were removed from the film on top of the mesas to the regions above the sidewalls and only TDs associated with 90° misfit dislocations remained. We suggest that this is due to pinning of the TDs associated with 60° misfit dislocations at the mesa edges and we have presented an explanation for this pinning in terms of the stress conditions at the {111} oriented mesa edges. In addition, this leads us to suggest that in order to obtain minimum TD density it is imperative to prevent formation of 90° misfit dislocation during lattice mismatched heteroepitaxial growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357572
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  • 4
    Electronic Resource
    Electronic Resource
    Structural and optical properties of pseudomorphic InxGa1−xN alloys (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1757-1759 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thick (225 nm) InxGa1−xN layers, grown on 5 μm thick GaN, were found by x-ray diffraction (XRD) measurements to be pseudomorphic up to x=0.114. Transmission electron microscopy showed that no misfit or additional threading dislocations were created at the InxGa1−xN/GaN interface. Composition of the overlayers was determined by Rutherford backscattering spectrometry and correlated to both the a and c lattice constants from XRD. It was found that Vegard's law is applicable at these compositions, if the biaxial strain is included. Biaxial strain must also be considered to accurately determine the bowing parameter as shown by optical transmission measurements. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122272
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  • 5
    Electronic Resource
    Electronic Resource
    Phase separation in InGaN/GaN multiple quantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1730-1732 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Evidence is presented for phase separation in In0.27Ga0.73N/GaN multiple quantum wells. After annealing for 40 h at a temperature of 950 °C, the absorption threshold at 2.95 eV is replaced by a broad peak at 2.65 eV. This peak is attributed to the formation of In-rich InGaN phases in the active region. X-ray diffraction measurements show a shift in the diffraction peaks toward GaN, consistent with the formation of an In-poor phase. A diffraction peak corresponding to an In-rich phase is also present in the annealed material. Nanoscale In-rich InGaN precipitates are observed by transmission electron microscopy and energy dispersive x-ray chemical analysis. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121166
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  • 6
    Electronic Resource
    Electronic Resource
    The influence of inversion domains on surface morphology in GaN grown by molecular beam epitaxy (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3486-3488 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Growth of GaN by rf-plasma molecular beam leads to different surface morphologies for nitrogen-rich growth versus gallium-rich growth. Nitrogen-rich growth produces a significant density of pyramidal hillocks while gallium-rich growth results in flat surfaces. Differences in surface morphology were directly linked to the presence of inversion domains which originated in the nucleation layer. Nitrogen-rich growth and growth under atomic hydrogen enhanced the growth rate of inversion domains with respect to the surrounding matrix, while growth under Ga-rich conditions resulted in a more nearly equal growth rate. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120367
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  • 7
    Electronic Resource
    Electronic Resource
    Structure of GaN films grown by hydride vapor phase epitaxy (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2283-2285 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of GaN films grown by hydride vapor phase epitaxy on sapphire substrates has been studied by x-ray diffraction, transmission electron microscopy (TEM), and atomic force microscopy. Films, 15–80 μm thick, were grown on c-plane sapphire that were either pretreated with GaCl or contained a ZnO sputter deposited layer. The defect density, for both types of films, was found by plan view TEM to range between mid-107 to mid-108 dislocations/cm2 despite very different structural defects at the film/substrate interface. Nanovoids were found; however, no cracks were observed in the films that were investigated by TEM. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120051
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  • 8
    Electronic Resource
    Electronic Resource
    Misfit dislocations in ZnSe grown on vicinal Si(001) substrates (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 869-871 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High resolution electron microscopy (HREM) has been used to study misfit dislocations of ZnSe films grown on vicinal Si(001) substrates tilted 4° towards the [11¯0] axis. In images taken with the electron beam parallel to the [11¯0] direction, 60° dislocations were found to predominate whereas mostly Lomer dislocations or closely spaced 60° dislocations (separated by 〈2 nm) were observed in images taken in the orthogonal direction. A model is presented here to explain the formation of the asymmetric dislocation structure on the basis of mechanisms for propagation and formation of misfit dislocations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112186
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  • 9
    Electronic Resource
    Electronic Resource
    Inversion domains in GaN grown on sapphire (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2394-2396 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Planar defects observed in GaN films grown on (0001) sapphire have been identified as inversion domain boundaries (IDBs) by a combination of high resolution transmission electron microscopy, multiple dark field imaging, and convergent beam electron diffraction techniques. Films grown by molecular beam epitaxy (MBE), metalorganic vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE) were investigated and all were found to contain IDBs. The IDBs in the MBE and HVPE films extended from the interface to the film surface and formed columnar domains that ranged in width from 3 to 20 nm in the MBE films and up to 100 nm in the HVPE films. For the films investigated, the MBE films had the highest density, and the MOCVD films had the lowest density of IDBs. The nucleation of inversion domains (IDs) may result from step-related inhomogeneities of the GaN/sapphire interface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117648
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  • 10
    Electronic Resource
    Electronic Resource
    Stripe-width dependence of threshold current for gain-guided AlGaInN laser diodes (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 404-406 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The threshold current density of narrow-stripe gain-guided nitride laser diodes increases very rapidly as the stripe width is made narrow. To examine this behavior, waveguide simulations, incorporating the complex refractive indices associated with optical gain, have been used to analyze the lateral optical modes of gain-guided laser diodes. Threshold current was then determined from the gain–current relationship of our laser material, which was obtained experimentally. These evaluations reveal that gain guiding, coupled with a carrier-induced index depression, offer a reasonable explanation for the rapid increase in threshold when the stripe width becomes less than 5 μm. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123084
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