Tetragonal and monoclinic forms of GexSi1−x epitaxial layers

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Abstract
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.