Structure imaging of commensurate GexSi1−x/Si(100) interfaces and superlattices

High resolution electron microscopy is used to study interfacial quality in commensurate GexSi1−x systems grown by molecular beam epitaxy. Structure images of interfaces have been obtained, yielding atomic-scale information about sharpness and smoothness. From careful consideration of image contrast mechanisms at the interface, it is shown that variations in germanium concentration as low as about 5% may be detected under optimum conditions. Single interfaces of GexSi1−x exhibit no detectable diffusion of germanium into the silicon substrate and are locally sharp, but are not constrained to a single atomic plane. Interfacial quality is retained in a commensurate twenty-period 75-Å Ge0.4Si0.6/250-Å Si(100) superlattice. The techniques described here are also applicable to other compositional phase boundaries such as in III-V heterostructures.