Metal-organic chemical vapor deposition of single domain GaAs on Ge/GexSi1-x/Si and Ge substrates

The current work investigates the sublattice orientation of GaAs on (001) Ge/GexSi1-x/Si and Ge substrates offcut 6 degrees 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 degrees sublattice rotation between the two possible GaAs phases. One sublattice orientation dominates at film nucleation temperatures > 600 degrees C, another dominates at nucleation temperatures < 500 degrees 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. (C) 2000 American Institute of Physics. [S0021-8979(00)01305-0].