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  • 1
    Electronic Resource
    Electronic Resource
    Effect of oxygen pressure on the synthesis of YBa2Cu3O7−x thin films by post-deposition annealing (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6569-6585 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of ambient oxygen pressure on the synthesis of epitaxial YBa2Cu3O7−x films on (100) SrTiO3 substrates by post-deposition annealing of amorphous precursor films was studied for oxygen partial pressures pO2 between 1.0 and 8.0×10−5 atm and annealing temperatures between 890 and 650 °C. A pO2−1/T diagram containing recent literature data regarding YBa2Cu3O7−x oxygen stoichiometry, phase stability, and liquid-phase formation was compiled to provide guidance for the selection and interpretation of annealing conditions. The results evidence a strong dependency of growth properties on the oxygen pressure with enhanced c-oriented epitaxy at lower pO2 values. A particularly interesting result is the formation of predominantly c-oriented films at 740 °C and pO2=2.6×10−4 atm (0.2 Torr). Similar to YBa2Cu3O7−x films produced by in situ laser ablation at the same temperature and oxygen pressure, the films exhibited low ion channeling yields (χmin〈0.1) and a dense (smooth) surface morphology, while critical currents at 77 K were well in excess of 1 MA/cm2. From the observed systematic variation of structural film properties with synthesis conditions, annealing lines were derived indicating (T-pO2) combinations for either c- or a-oriented epitaxial growth. A comparison is made between these lines and synthesis conditions for in situ film growth as compiled recently by Hammond and Bormann [Physica C 162–169, 703 (1989)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348868
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  • 2
    Electronic Resource
    Electronic Resource
    InGaAs/InP quantum well intermixing studied by cross-sectional scanning tunneling microscopy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4815-4823 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cross-sectional scanning tunneling microscopy (STM) is used to study lattice matched InGaAs/InP quantum well (QW) intermixing induced by ion implantation and thermal annealing. Different strain development in QWs (determined by STM topography of elastic relaxation in cross sectionally cleaved samples) is found to be dependent upon the range of the implanted ions relative to the QWs. It is found that the quantum wells remain latticed matched to the barrier layers after intermixing when ions are implanted through the multiple quantum well (MQW) stack. A shallow implantation in which ions are implanted into the cap layer above the MQW stack leads to tensilely strained wells and compressively strained interfaces between wells and barriers. The strain development in the latter case is attributed to different degrees of interdiffusion on the group III and group V sublattices. Finite element elastic computations are used to extract the group V and group III interdiffusion length ratio, and results using different diffusion models are compared. A preferred group V interdiffusion in the case of shallow implantation is explained in terms of faster diffusing P related defects compared to In related defects. Images of as-grown QWs provide useful information about the growth technique related compositional fluctuations at the interfaces. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1361237
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  • 3
    Electronic Resource
    Electronic Resource
    Deposition of amorphous silicon films by hot-wire chemical vapor deposition (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6843-6852 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Device-quality a-Si:H films have been deposited by hot-wire chemical vapor deposition (HWCVD). We have investigated the influence of deposition parameters on the film growth and properties. The most important deposition and growth processes that influence the optoelectronic material properties of a-Si:H deposited by HWCVD are clarified. During the deposition process attention must be paid to accurately control the substrate temperature, which is a key parameter to obtain device-quality films. A heat transport model is presented to be able to correct for the heating of the substrate by the filaments. It is found that films deposited at high deposition temperatures are under a high compressive stress. We show how the hydrogen incorporation in the layer is influenced by hydrogenation of subsurface layers by the atomic hydrogen flux that is inherent to the HWCVD process. We further identify the fundamental differences between plasma enhanced CVD and HWCVD material. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370202
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  • 4
    Electronic Resource
    Electronic Resource
    Correlation of buffer strain relaxation modes with transport properties of two-dimensional electron gases (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6849-6854 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the effects of buffer strain relaxation on the transport properties of two-dimensional electron gases (2DEGs). The 2DEGs consist of modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterostructures grown lattice-mismatched to GaAs via compositionally step-graded InxGa1−xAs buffers, with different composition gradients, or lattice-matched to InP. We find a variation in 2DEG electronic properties which occurs simultaneously with large differences in epilayer tilt and mosaic spread in the step-graded buffers. This indicates a correlation between the mechanism of buffer strain relaxation and the 2DEG transport properties. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363751
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  • 5
    Electronic Resource
    Electronic Resource
    Scattering from strain variations in high-mobility Si/SiGe heterostructures (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6091-6097 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Computations of scattering rates from strain variations in high-mobility n-channel Si/SiGe heterostructures are presented, and the results compared with experiment. Two sources of strain variation are considered—interface roughness and misfit dislocations—both of which form to relieve strain in the Si channel layer which is under tension. Strain variations induced by interface roughness are demonstrated to provide a source of scattering which, for highly strained systems of the type considered here, is significantly larger than conventional geometrical roughness scattering. Misfit dislocations provide a source of localized scattering centers, and an appropriate formalism is developed to describe this case. For both types of scattering, reasonable agreement with measured mobilities is found for various values of channel thickness. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360549
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  • 6
    Electronic Resource
    Electronic Resource
    Unique x-ray diffraction pattern at grazing incidence from misfit dislocations in SiGe thin films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 89-96 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Grazing-incidence x-ray diffraction (GIXD) permits the direct measurement of in-plane lattice parameters of SiGe films that are too thin to yield good results from normal-geometry triple-axis techniques. A unique "X''-shaped pattern has been seen in H–K reciprocal space maps of diffracted x-ray intensity from SiGe films that have relaxed via a modified Frank–Read mechanism. Contours of intensity are seen along the 〈110〉 directions from the (4¯00) reciprocal lattice peak with the introduction of the first dislocations. For higher dislocation densities the X-shaped contours are anisotropically distorted and a satellite peak, corresponding to the lattice parameter for a partially relaxed film, becomes identifiable at lower H. In contrast, H–K reciprocal-space contours from thin SiGe films that have relaxed by roughening and subsequent random nucleation of dislocations display broad, oval-shaped contours centered at the (4¯00) reciprocal lattice point for the film. Numeric simulations of GIXD from a variety of dislocation arrangements were performed in order to understand the origin of the X pattern. We show that this pattern arises from an array of long misfit dislocations running in the 〈110〉 directions. The anisotropic distortion of the X pattern arises at higher dislocation densities from orthogonal intersections of dislocations with equal Burgers vector, which are characteristic of dislocation networks generated by the modified Frank–Read mechanism. We also verify that the measured values of the in-plane lattice parameter, together with the out-of-plane lattice parameter determined from the symmetric (004) reflection, lead to accurate calculation of the composition and strain in these SiGe layers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362776
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  • 7
    Electronic Resource
    Electronic Resource
    Preferred alignment of twin boundaries in YBa2Cu3Ox thin films and YBa2Cu3Ox/PrBa2Cu3Ox superlattices on SrTiO3 (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2174-2176 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of YBa2Cu3Ox thin films and YBa2Cu3Ox/PrBa2Cu3Ox superlattice films grown on (00L) SrTiO3 substrates has been studied using x-ray diffraction and transmission electron microscopy. The films consist of four symmetry-equivalent domains related by mutually perpendicular (hh0) and (hh¯0) twin boundaries. One twin orientation is often highly favored over the other. We have correlated this in-plane symmetry breaking with small miscuts of the substrate surface towards the [HH0] direction and propose that interfacial steps act as nucleation sites for twins. Thus, by controlling the surface normal, a technique is described for producing films containing aligned twin boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104997
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  • 8
    Electronic Resource
    Electronic Resource
    Phase stability for the in situ growth of Nd1+xBa2−xCu3Oy films using pulsed-laser deposition (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 96-98 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have determined the stability line in the 1/T−log[P(O2)] phase space for the synthesis of Nd1+xBa2−xCu3Oy (NdBCO) films. A systematic study of Tc, Jc, and ρ(T) dependence on oxygen partial pressure and temperature for the deposition of thin NdBCO films grown by pulsed-laser deposition was performed. The conditions for optimal NdBCO film growth were determined by varying oxygen partial pressure from 0.02 to 400 mTorr, and substrate temperature between 730 and 800 °C. The results show that the best NdBCO films are obtained at oxygen pressures in the range of 0.2–1.2 mTorr, depending on the substrate temperature. This is more than two orders-of-magnitude lower than the correspondent oxygen pressure appropriate for YBa2Cu3O7−δ film growth. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123162
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of wurtzite GaN lattice polarity based on surface reconstruction (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2114-2116 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We identify two categories of reconstructions occurring on wurtzite GaN surfaces, the first associated with the N face, (0001¯), and the second associated with the Ga face, (0001). Not only do these two categories of reconstructions have completely different symmetries, but they also have different temperature dependence. It is thus demonstrated that surface reconstructions can be used to identify lattice polarity. Confirmation of the polarity assignment is provided by polarity-selective wet chemical etching of these surfaces. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121293
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  • 10
    Electronic Resource
    Electronic Resource
    Epitaxial superconducting thin films of YBa2Cu3O7−x on KTaO3 single crystals (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1063-1065 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have grown thin YBa2Cu3O7−x films on single-crystal (001) KTaO3 substrates by means of coevaporation of Y, BaF2, and Cu, followed by an ex situ anneal in wet oxygen. The films are epitaxial in three dimensions, consisting of grains with either the c or the a axis of the YBa2Cu3O7−x unit cell perpendicular to the substrate. Films with a composition close to the 1:2:3 cation ratio exhibit sharp superconducting transitions at 90 K and critical current densities in excess of 0.3 MA/cm2 in zero magnetic field at 77 K. In Cu-rich films, the Y2Ba4Cu8O16–x phase with a Tc of 80 K is formed in grains with the c axis perpendicular to the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101426
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