OBSERVATION OF VERTICAL AND LATERAL GE SEGREGATION IN THIN UNDULATINGSIGE LAYERS ON SI BY ELECTRON-ENERGY-LOSS SPECTROSCOPY

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