Observation of vertical and lateral Ge segregation in thin undulating SiGe layers on Si by electron energy-loss spectroscopy

The local Ge composition in undulating Si0.8Ge0.2 layers on Si has been studied in a scanning transmission electron microscope using electron energy-loss spectroscopy. We observe Ge enrichment of the SiGe layer near the free surface (vertical Ge segregation in the growth direction) as well as Ge depletion of the ripple troughs compared to the peaks (lateral segregation). These lateral compositional fluctuations are likely to retard the generation of misfit dislocations and might be relevant to the Stranski-Krastanov growth of strained epitaxial alloy layers as well as to the self-organized growth of quantum dot structures. (C) 1997 American Institute of Physics.