The current work investigates the sublattice orientation of GaAs on (001) Ge/GexSi1−x/Si and Ge substrates offcut 6° to [110] as a function of atmospheric pressure metal-organic chemical vapor deposition (MOCVD) nucleation conditions. Anisotropic sidewall etching of the GaAs films and differential interference contrast microscopy of the GaAs film surface reveal a 90° sublattice rotation between the two possible GaAs phases. One sublattice orientation dominates at film nucleation temperatures >600 °C, another dominates at nucleation temperatures <500 °C. Incomplete transition between the two sublattice orientations during pregrowth thermal cycling accounts for the appearance of localized bands and clouded regions of antiphase disorder, marking a shift in the polarity of the GaAs film. We have concluded that the observed domain rotation results from a temperature-dependent surface transition prior to actual GaAs nucleation. In particular it is suspected that background arsenic levels in the MOCVD system induce the observed transition. We propose that localized antiphase disorder reflects kinetically limited arsenic dimer orientation on the prenucleation germanium surface. Conditions for the complete suppression of antiphase disorder under optimized growth conditions are described and demonstrated by transmission electron microscopy.

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A high bulk minority-carrier lifetime in GaAs grown on Si-based substrates is demonstrated. This was achieved by utilizing a step-graded Ge/GeSi buffer (threading dislocation density 2×106 cm−2) grown on an offcut (001) Si wafer, coupled with monolayer-scale control of the GaAs nucleation to suppress antiphase domains. Bulk minority-carrier lifetimes (τp) were measured using room-temperature time-resolved photoluminescence applied to a series of Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As double-heterojunction structures doped n=1.1×1017 cm−3 with GaAs thicknesses of 0.5, 1.0, and 1.5 μm. A lifetime τp=7.7 ns was determined for GaAs grown on Si. The extracted interface recombination velocity of 3.9×103 cm/s is comparable to recombination velocities found for Al0.3Ga0.7As/GaAs interfaces grown on both GaAs and Ge wafers, indicating that the crosshatch surface morphology characteristic of strain-relaxed Ge/GeSi surfaces does not impede the formation of high-electronic-quality interfaces. These results hold great promise for future integration of III–V minority-carrier devices with Si wafer technologies.

Growth kinetics and modeling of selective molecular beam epitaxial growth of GaAs ridge quantum wires on prepatterned nonplanar substrates Molecular beam epitaxial growth of InAs/AlGaAsSb deep quantum well structures on GaAs substratesThe epitaxial growth of GaAs on Si substrates through the use of a Ge/graded Si 1Ϫx Ge x /Si buffer layer would allow monolithic integration of GaAs-based opto-electronics with Si microelectronics. As an initial step toward this goal, this study examines factors which influence the quality of GaAs growth by molecular beam epitaxy ͑MBE͒ on bulk Ge substrates. Key findings include the need for an epitaxial Ge smoothing cap deposited in the MBE chamber, the significant detrimental effect of As overpressure on the resultant GaAs crystalline quality, and the efficiency of a very thin (ϳ3 nm) migration enhanced epitaxy ͑MEE͒ nucleation layer at suppressing both anti-phase domain ͑APD͒ formation and interdiffusion across the GaAs/Ge heterointerface. Using this developed optimized growth process, APD-free GaAs on Ge is obtained which has undetectable Ga and Ge cross-diffusion, and As diffusion into the substrate at р1ϫ10 18 cm Ϫ3 . Preliminary results for growths on Ge/Si 1Ϫx Ge x /Si substrates are also presented.

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