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  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.352868
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.352120
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353825
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.102528
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  • 5
    Digitale Medien
    Digitale Medien
    Role of vanadium in organometallic vapor phase epitaxy grown GaAs (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1772-1774 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electrical and photoluminescent properties of vanadium incorporated into GaAs epitaxial layers from a VO(OC2H5)3 source during organometallic vapor phase epitaxy were examined. The vanadium concentration in the GaAs was controllably varied from 1016 to 1018 atoms cm−3. Deep level transient spectroscopy showed the presence of an electron trap at Ec−0.15 eV which increased in concentration with vanadium content of the epitaxial layers. A maximum value of 8×1015 cm−3 for this trap was obtained. There were no midgap electron traps associated with vanadium. In intentionally Si-doped epitaxial layers, co-doping with vanadium was observed to have no effect in reducing the carrier density when the Si concentration was ≥4×1016 cm−3. The net carrier concentration profiles resulting from 29Si implantation into GaAs containing 1018 cm−3 of total V had sharper tails than for similar implantation into undoped material, indicating the presence of less than 1016 cm−3 V-related acceptors. Photoluminescent spectra exhibited the characteristic V+3 intracenter emission at 0.65–0.75 eV. No other deep level photoluminescence was detected. For a V concentration of 1016 cm−3 only 2.5×1013 cm−3 was electrically active. Over the entire V concentration investigated this impurity was predominantly (≥99%) inactive.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.101287
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  • 6
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.102866
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  • 7
    Digitale Medien
    Digitale Medien
    An analysis of dislocation reduction by impurity hardening in the liquid-encapsulated Czochralski growth of 〈111〉 InP (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 4383-4389 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Excessive impurity additions have been widely used to suppress dislocation generation in the liquid-encapsulated Czochralski (LEC) growth of InP. We have analyzed this approach by means of the quasi-steady-state heat transfer/thermal stress model. A strong motivation for the investigation was provided by the recent measurement of the critical resolved shear stress σCRS of InP as a function of temperature in the range 748–948 °K for several Ge and S concentrations. The experimental data were analyzed by the method of least squares via the usually accepted logarithmic dependence of σCRS on reciprocal temperature. The extrapolated values of σCRS exhibit a monotonic increase with impurity addition at temperatures near the melting point. Introducing the σCRS and realistic estimates of other physical properties (thermal diffusivity, thermal expansion coefficient, elastic constants, etc.) in the thermal stress model, the dislocation distribution pattern in a {111} substrate cut from a 〈111〉 boule was constructed. This necessitated a suitable recasting of the formalism that was previously applicable only to the {100} orientation. The computed dislocation contour maps on {111} wafers display sixfold symmetry resembling the "Star of David,'' in overall agreement with etch-pit patterns. InP crystals 2.5 cm in diameter grown in a standard high ambient temperature gradient but containing a large amount of Ge ((approximately-equal-to)1019 cm−3) are predicted and observed to be dislocation-free. On the other hand, in nominally undoped material a large density of defects is forecast, especially at the periphery, in line with the etchpit configuration. Intermediate doping levels (∼1017 cm−3 Ge, ∼1018 cm−3 S) reduce the density in the core but leave the outer edge essentially unaltered.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.335528
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  • 8
    Digitale Medien
    Digitale Medien
    Surface polygonization on GaAs wafers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1468-1471 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Polygonized surface structure produced by furnace annealing GaAs wafers was studied by optical and scanning electron microscopy. The surface structure was revealed by chemically etching wafers which had been implanted with silicon and subjected to a furnace annealing cycle. Cathodoluminescence micrographs demonstrate an absence of impurity segregation to the polygon boundaries. No correlation was found between growth-induced dislocations and the polygonal networks. It is proposed that the surface structure results from a vacancy-condensation process. Related surface effects were observed for rapidly annealed wafers. A correlation between the furnace annealed and rapidly annealed GaAs is presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.341819
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  • 9
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.105727
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  • 10
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.108956
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