Oxidation-enhanced interdiffusion in Si1-xGex/Si1-yGey superlattices

The effects of Si surface oxidation on Si-Ge interdiffusion in epitaxial heterostructures are presented. Single crystal Si1-xGex/Si1-yGey superlattices, with a nominal Ge composition of 8.5 at. %, were grown by low-pressure chemical vapor deposition onto Si (001) substrates. An epitaxial Si cap, which was partially consumed during postdeposition annealings in dry O-2, was grown onto these superlattices. We observed an enhancement of Si-Ge interdiffusion kinetics for the case of oxidation annealings when compared to inert atmosphere annealings. X-ray multilayer scattering measurements were used to quantify the effects of nonequilibrium point defect concentrations created during Si oxidation on the interdiffusivity of Si and Ge over the temperature range of 770-870 degrees C. The activation enthalpy and preexponential constant for the interdiffusivity at this Si-Ge composition, which were determined by analysis of the x-ray multilayer satellite intensity decay after annealing, were found to be 3.99 +/- 0.2 eV and 1.32 cm(2)/s, respectively. The extent of the observed interdiffusivity enhancement caused by Si surface oxidation is significantly less than that reported for Si self-diffusion. This suggests a smaller interstitial-mediated component for Si-Ge interdiffusion than for Si self-diffusion. (c) 2007 American Institute of Physics.