Tetragonal and monoclinic forms of GexSi1-x epitaxial layers.

The effect of strains on the local crystallographic symmetry and structure of a Si/GexSi1-x model heterostructure grown on a (100) silicon substate was studied using convergent beam electron diffraction techniques and a cross-sectional specimen geometry. The alloy layers are seen to distort into relaxed tetragonal and monoclinic structures which are dependent on position and/or alloy composition. These observations can be explained in terms of strain relaxation in a thin-film specimen and deviations of the substrate from a perfect (100) orientation. The results have implications not only for the use of cross-sectioned specimens in the characterization of strained-layer heterostructures, but also for the band engineering of Si/GexSi1-x strained-layer superlattices and other materials which are grown on vicinal (100) and other low-symmetry substrate orientations. In particular relaxed tetragonal and monoclinic structures may be quite relevant to the emerging science of strain-induced lateral confinement of carriers in quantum well semiconductors. [ABSTRACT FROM AUTHOR]