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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Measurements of alloy composition and strain in thin GexSi1−x layers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 8098-8108 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The utility of Raman spectroscopy for the simultaneous determination of composition and strain in thin GexSi1−x layers has been investigated. Using data from the literature and new data for the strain shift of the Si-Si phonon mode presented here, we show how Raman spectra provide several different means of measuring composition and strain in samples as thin as 200 A(ring). We demonstrate that for largely relaxed layers with compositions near x=0.30, Raman scattering can measure the composition, x, with an accuracy of ±0.015 and the strain, ε, with an accuracy ±0.0025. The accuracy of the alloy composition obtained from Raman spectra is comparable or, in the case of very thin layers, superior to that measured by other techniques such as x-ray diffraction, electron microprobe, and Auger electron spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356554
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  • 3
    Electronic Resource
    Electronic Resource
    Nucleation of dislocations in SiGe layers grown on (001)Si (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3968-3977 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive x-ray-diffraction study of the variation of the tilt angle between a Si1−xGex layer and the (001) Si substrate is presented. Such measurements provide the basis of a new method for determining the nucleation activation energy of misfit dislocations. A detailed model, independent of the particular relaxation mechanism, is derived which relates the tilt angle to the nucleation activation energy on the different slip systems and to the density of misfit dislocations. The model has been applied to the modified Frank–Read mechanism observed in graded samples. Relaxation occurs in such samples for strain in the range 0.002≤ε≤0.006 with an activation energy of about 4 eV. The critical thickness for growth of a strained layer is shown to be smaller when the substrate is miscut than when it is well oriented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356992
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  • 4
    Electronic Resource
    Electronic Resource
    Objective measurement of anxiety in hypertensive pregnant women managed in hospital and in the community (1992)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 99 (1992), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Objective To determine whether pregnant hypertensives women are more anxious when monitored in hospital or at homes.Design Prospective randomized controlled trial.Setting Rosie Maternity Hospital and women's homes.Subjects Ninety-nine pregnant hypertensive women: 50 had their blood pressure measured telemetrically from home, and 49 had it measured in hospital.Main outcome measures Number of episodes of monitoring, duration of monitoring, mean blood pressure during monitoring, gestational age at delivery, trait and state anxiety levels.Results There were no significant differences in anxiety levels, or in any other outcome measure, between the home and hospital groups.Conclusion When blood pressure is being monitored serially in pregnant hypertensive women, there is no measurable difference in their anxiety levels, whether they are in hospital or at home.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1992.tb14495.x
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  • 5
    Electronic Resource
    Electronic Resource
    The characterization of indium desorbed Si surfaces for low temperature surface cleaning in Si molecular beam epitaxy (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 1854-1859 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To investigate the feasibility of using indium to replace Ga as an agent for silicon surface cleaning at lower substrate temperature in ultrahigh vacuum, we have examined the in-diffusion of indium and the surface defects introduced into silicon for various indium desorption processes. TEM, SEM, AES, SIMS, EDAX, and DLTS, as well as spreading resistance measurements, were used to characterize the samples. For the dynamic desorption case, which simulated the actual cleaning procedure, no significant surface defects were identified, nor was there any indium in the near surface region of the silicon substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336014
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  • 6
    Electronic Resource
    Electronic Resource
    Noise spectroscopy of deep level (DX) centers in GaAs-AlxGa1−xAs heterostructures (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1541-1548 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the generation-recombination noise from the donor-related DX centers in current biased GaAs/AlxGa1−xAs heterostructures from 1 Hz to 25 kHz and from 77 to 330 K. A significant noise contribution from these traps is observed even at Al mole fractions below 0.2, where the trap level is resonant with the conduction band. The activated behavior of the noise spectrum from this resonant level is very similar to that observed at higher Al mole fractions, when the level lies deep in the fundamental gap. This result can be predicted, based on the recently elucidated relationship of the trap level to the band structure of AlxGa1−xAs. In accordance with other experimental results, the noise spectra demonstrate that the emission and capture kinetics of the level are unperturbed by its resonance with the conduction band. We briefly discuss some implications of these results for heterostructure transistor design.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339938
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  • 7
    Electronic Resource
    Electronic Resource
    DX centers in AlGaAs p-n heterojunctions and heterojunction bipolar transistors (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3234-3236 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: DX centers are found to cause the capacitance of an AlGaAs/GaAs p-n heterojunction at 77 K to behave like that of a p-i-n diode. Exposure to light causes the capacitance to behave like a normal p-n junction. It is argued that the presence of DX centers has only a small effect on the switching properties heterojunction bipolar transistors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339326
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  • 8
    Electronic Resource
    Electronic Resource
    Barrier heights and electrical properties of intimate metal-AlGaAs junctions (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 1516-1522 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of the Schottky barrier height of Mo-n:AlGaAs junctions, fabricated in situ by molecular beam epitaxy, on the Al mole fraction (x) was determined by internal photoemission measurements and by activation energy plots of the current versus voltage dependence on temperature. Both techniques yielded similar values. The difference in barrier height of Mo-AlGaAs as a function of x, compared to that of Mo-GaAs, was found to be equal to the conduction band discontinuity in AlGaAs-GaAs heterojunctions for Al concentrations in the range 0≤x≤0.4. For x〉0.4, values of the barrier heights were somewhat lower than values of the band discontinuity; however, both dependencies on x were quite similar. The temperature dependence of the current-voltage characteristics showed that thermionic emission was the dominant transport mechanism at forward bias for temperatures higher than 250 K. At lower temperatures, current transport was governed by thermionic field emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338085
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  • 9
    Electronic Resource
    Electronic Resource
    Deep electron traps in GaAs/n-AlxGa1−xAs single-quantum wells (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2408-2414 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deep-level-transient spectroscopy on molecular-beam epitaxially grown square GaAs/ n-AlxGa1−x As (x=0.24–0.39) single-quantum wells shows a series of electron traps in the AlGaAs with energies EC−ET at 0.12, 0.22, 0.29, 0.52, and 0.63 eV and with concentrations of about 5×1015 cm−3. The defects are located in the upper AlGaAs layer near the GaAs well layer. The trap concentrations and the widths of the spatial trap distributions (typically 15 nm) are independent of the well width. For all traps, a nonexponential capture process which is logarithmic in time is observed. Time-dependent depth profiling shows a virtual shift of the trap distribution to the surface for shorter filling pulses. Both effects are due to the nonabrupt depletion edge (Debye tail). No direct emission from the quantum wells is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341674
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  • 10
    Electronic Resource
    Electronic Resource
    Deep levels in p-type GaAs grown by metalorganic vapor phase epitaxy (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4975-4986 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a detailed deep level transient spectroscopic study in p-type Mg- and Zn-doped GaAs epitaxial layers grown by metal-organic vapor phase epitaxy. Dependence of deep level structures on doping concentrations and growth temperatures has been investigated. Over a wide range of growth conditions, four hole traps and an electron trap ranging in activation energy from 0.18–0.79 eV were measured in GaAs:Mg while only a single hole trap has been observed in GaAs:Zn.The presence of a certain trap and its concentration in GaAs:Mg depends mainly on the doping concentration in the layers. The total trap concentration in the GaAs:Mg decreases rapidly with doping concentration for p〉4×1017 cm−3. The physical and chemical origins of several of these traps have been identified. The Mg-doped GaAs always exhibited a greater concentration of midgap trap levels than the Zn-doped material, regardless of dopant concentration or growth temperature. The overall defect structure and dopant incorporation characteristics indicate that Zn is the preferred dopant species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342447
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