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  • 1
    Electronic Resource
    Electronic Resource
    Quasi-steady-state heat transfer/thermal stress model for dislocation generation in the vertical gradient freeze growth of GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4016-4022 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have formulated a tractable model of the vertical gradient freeze (VGF) process for GaAs, providing dislocation density contour lines in terms of geometrical and physical parameters. First, the temperature distribution in a cylindrical boule has been determined in closed form involving modified Bessel functions of the first kind, order zero (I0) by solving the quasi-steady-state partial differential equation for heat conduction. Subsequently, the principal thermoelastic stress components have been evaluated and then resolved in the {111}, 〈11¯0(approximately-greater-than) slip system which in excess of the critical resolved shear stress (CRSS) introduce dislocations by slip. We present dislocation density contour maps for 2- and 3-in.-diam undoped (100) GaAs grown by VGF under a variety of linear thermal gradients (v) imposed on the periphery of the boule. We show that for large v the dislocation distribution is similar to that observed in liquid-encapsulated Czochralski (LEC) material but lowering v effectively suppresses dislocation generation even in boules larger than 2 in. in diameter. A comparison of dislocation generation in VGF and standard LEC growth using very recent CRSS data is also given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352868
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  • 2
    Electronic Resource
    Electronic Resource
    Silicon-doping level dependent diffusion of Be in AlGaAs/GaAs quantum well lasers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4648-4654 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated Be diffusion during molecular beam epitaxial growth of GaAs/AlGaAs graded index separate confinement heterostructure laser structures using secondary ion mass spectrometry (SIMS). For growth at 700 °C we find that Be from the p-type AlGaAs cladding layer diffuses into the quantum well and beyond. As a result, the p-n junction is displaced from the heterojunction. The extent of Be diffusion is found to depend on the dopants in the graded index (GRIN) regions adjoining the GaAs active layer. When the GRIN segments are left intentionally undoped, Be diffuses through the entire p-side GRIN, the quantum well active and a significant portion of the n-side GRIN. However, when the GRIN regions are doped, respectively, with Be and Si on the p and n sides, the displacement of the p-n junction caused by Be diffusion is significantly reduced. Assuming that Be diffuses from a constant source at the surface into a n-type layer as a singly charged interstitial donor, our analysis predicts that increasing the doping of the n layer retards the diffusion of Be while that of the p layer enhances it. Further, including the electric field of the p-n junction in the model leads to peaks and inflections resembling those observed in the experimental SIMS profiles. In view of Be-related oxygen contamination and Be diffusion on the p-side GRIN region, Be should be dispensed with on the p side, however, Si addition on the n side is beneficial as it minimizes Be diffusion and p-n junction displacement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352120
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  • 3
    Electronic Resource
    Electronic Resource
    A comparison of reducing the dislocation densities in GaAs grown by the vertical gradient freeze and liquid-encapsulated Czochralski techniques (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 477-479 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have recently applied the quasi-steady state heat transfer/thermal stress model for dislocation generation to the vertical gradient freeze (VGF) process for GaAs, permitting a direct comparison with the original treatment of liquid-encapsulated Czochralski (LEC) growth. Very recent high temperature critical resolved shear stress (CRSS) data on undoped VGF and In-doped LEC specimens were used. We show that the ∼threefold increase in CRSS with In is sufficient to inhibit defect formation in the central ∼75% of 3 in. diameter LEC wafers grown in a high ambient temperature gradient, duplicating the etch-pit density (EPD) data. Undoped VGF wafers are predicted to be nearly dislocation-free. The theoretical results on 3 in. material track the low EPD counts in both the 〈100〉 and 〈110〉 directions in a 5 K/cm gradient imposed on the crystals' surface. We also discuss the origin of dislocations in regions free of thermal stresses and propose their suppression by the addition of a small amount of In in VGF experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353825
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  • 4
    Electronic Resource
    Electronic Resource
    Inverse scattering on the line for a Dirac system (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 3015-3030 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The whole-line version of the Gelfand–Levitan–Marchenko (GLM) equation for a Dirac system is studied. A new derivation of the GLM equation is given, under weaker hypotheses than Frolov's earlier treatment [Sov. Math. Dokl. 13, 1468 (1972)], and the complete inversion is carried out in some explicit cases in which a spectral gap is present. Previous calculations of this type are restricted either to a scalar potential or degenerate gap. Applications are discussed in connection with optical couplers and soliton equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529046
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  • 5
    Electronic Resource
    Electronic Resource
    Redistribution of Zn in GaAs-AlGaAs heterojunction bipolar transistor structures (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1251-1253 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The redistribution of Zn in the base region of GaAs-AlGaAs heterojunction bipolar transistor structures during growth by organometallic vapor phase epitaxy has been examined with respect to the presence of Si doping in the emitter-contact, emitter, and collector/subcollector layers, and as a function of Zn doping concentration and Si counterdoping level in the p+ base. For a growth temperature of 675 °C the Zn shows no significant redistribution up to concentrations of 3×1019 cm−3 without Si doping. The addition of Si to the adjacent AlGaAs emitter and collector/subcollector layers causes substantial diffusion of Zn from the base, while Si doping of the GaAs emitter contact results in even greater Zn redistribution. Under these conditions, the Zn concentration in the base attains a maximum value of ∼7×1018 cm−3. Silicon counterdoping in the base region retards the Zn diffusion, while strain introduced by an InGaAs cap layer has no effect on the Zn redistribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102528
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  • 6
    Electronic Resource
    Electronic Resource
    Growth of high quality AlGaAs by metalorganic molecular beam epitaxy using trimethylamine alane (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2654-2656 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: AlGaAs grown by metalorganic molecular beam epitaxy (MOMBE) has been problematic due to oxygen and carbon contamination, particularly when triethylaluminum (TEAl) has been used as the aluminum source. Consequently, we have investigated trimethylamine alane (TMAAl) as a potential replacement for the conventional metalorganic Al sources. AlGaAs films with excellent structural and optical properties have been grown with this source. Photoluminescence intensities from AlGaAs grown by MOMBE at 500 °C using TMAAl are comparable to those from material grown by metalorganic chemical vapor deposition at 675 °C using triethylaluminum (TMAl). Carbon and oxygen levels in MOMBE-grown AlGaAs are drastically reduced in comparison to similar films grown with TEAl.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102866
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  • 7
    Electronic Resource
    Electronic Resource
    Residual oxygen levels in AlGaAs/GaAs quantum-well laser structures: Effects of Si and Be doping and substrate misorientation (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 3270-3272 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oxygen forms nonradiative recombination centers in GaAs and AlGaAs, and is a common contaminant in AlGaAs, irrespective of the growth technique. We find that O tends to accumulate near the GaAs active region of an AlGaAs/GaAs quantum-well laser prepared by molecular beam epitaxy. Moreover, the Be-doped Al0.6Ga0.4As cladding layer has a higher O content than its Si-doped counterpart. We present evidence that Si-doping suppresses, and Be doping favors incorporation of O in AlGaAs. In undoped and Si-doped AlGaAs, the incorporation of O is further reduced by tilting the (100) GaAs substrates towards 〈111〉A. We propose that Be forms stable Be-O complexes in AlGaAs, and thus, there is virtually no desorption of incorporated O. But in Si-doped AlGaAs, O content is reduced due to reaction between group III suboxides and Si, resulting in the formation and desorption of volatile SiO (g). The study suggests that Be doping should be avoided in the p-side of the GRIN region of a laser structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105727
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  • 8
    Electronic Resource
    Electronic Resource
    Thermodynamic interpretation of quaternary (InGaAsP) layer uniformity grown by low-pressure metalorganic vapor phase epitaxy (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 360-362 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: According to a recent study, the compositional nonuniformity for group V sites of quaternary (Q) In0.68Ga0.32As0.7P0.3 layers (λ=1.35 μm) grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) on 50 mm diam InP wafers was reduced from 3% to 1% when tertiary butyl phosphine (TBP)+AsH3 instead of PH3+AsH3 or TBP+tertiary butyl arsine (TBAs) were employed. In this letter we offer a thermodynamic interpretation of these observations. Under LP-MOVPE conditions at a total pressure of 0.08 atm for fully decomposed group V precursors diluted with H2, we show that while the dominant species are the tetramers, the concentration of the dimers is significant and becomes more prominent with rising temperature (T). Examining the [As/P] ratio in the gas phase as a function of reciprocal T, we demonstrate that in the MOVPE range (900–950 K) the slope of these curves changes from steep to moderate and then nearly flat for the sources AsH3+PH3, TBAs+TBP, and AsH3+TBP, respectively. The insensitivity of the [As/P] ratio to the ∼30 K gradient over the susceptor when combining AsH3 and TBP suggests a very effective method to assure compositional uniformity in Q layers prepared by LP-MOVPE. Uniformity results for atmospheric pressure MOVPE employing AsH3 and PH3 are also consistent with the thermodynamic argument.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108956
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  • 9
    Electronic Resource
    Electronic Resource
    Seasonal and interannual variability in krill (Nyctiphanes australis) stocks and their relationship to the fishery for jack mackerel (Trachurus declivis) off eastern Tasmania, Australia (1993)
    Springer
    Marine biology 116 (1993), S. 9-18 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nyctiphanes australis was collected from the east coast of Tasmania between January 1989 and April 1991. Density and biomass were significantly higher in autumn than in any other season. The population was dominated by juveniles, except in autumn and spring 1990 when there was a significant increase in the proportion of adults. Our data indicated that N. australis does not regularly migrate vertically and that it forms aggregations of particular size classes which vary both temporally and spatially. Stomach fullness in Trachurus declivis, a major predator of N. australis, rose to a peak in autumn when N. australis stocks and the monthly catches by the fishery for T. declivis were at their highest. The stomachs of T. declivis were also dominated by adult size classes during this period. The virtual absence of N. australis in 1989 and the subsequent failure of the T. declivis fishery in that year underline the interrelationship between these two species. We suggest that this was the result of an influx of subtropical northern waters low in nutrients onto the shelf, which corresponded with a major La Niña “cold event” at that time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350726
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  • 10
    Electronic Resource
    Electronic Resource
    Thermodynamic properties of AsH3 and its subhydrides (1993)
    Springer
    Journal of materials science 4 (1993), S. 215-224 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The thermodynamic properties of AsH3 and its subhydrides AsH and AsH2 have been evaluated from critically assessed or estimated spectroscopic data. The calculation of thermodynamic functions (free-energy function, entropy, enthalpy, and heat capacity) is based on statistical thermodynamics. For the first time, for all three species a complete set of these functions has been generated between 0 and 1600 K in tabular form. A combination of the free-energy functions with the standard enthalpies of formation of hydrides (derived from the photoionization mass-spectrometric bond energy values of Berkowitz) permits the determination of the gas phase composition in the pyrolysis of AsH3 during the MOMBE (CBE), HS-MBE, or MOCVD growth of III–V epitaxial layers that include As. Using a free-energy minimization technique, the equilibrium concentrations of AsH, AsH2, AsH3, As, As2, As4, H and H2 have been obtained at 1.013, 3.039 × 103 and 1.013 × 105 Pa (1 atm) in the temperature range between 800 and 1500 K. In the case of MOMBE, under equilibrium conditions in the hydrate cracker, the removal of carbon-containing radicals or oxygen is facilitated by atomic H and AsH with partial pressures of ~3.33 × 10−4 and 1.87 × 10−5 Pa, respectively, at 1300 K. In contrast, in low pressure MOCVD the species AsH and AsH2 are equally prominent, while in atmospheric pressure MOCVD the dominant subhydride is AsH2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00224744
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