Structure imaging of commensurate Ge(x)Si(1-x)/Si(100) interfaces and superlattices.

High resolution electron microscopy is used to study interfacial quality in commensurate Ge(x)Si(1-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 defected under optimum conditions. Single interfaces of Ge(x)Si(1-x) exhibit no detectable diffusion of germanium into the silicon substrate and are locally sharp, but are not constrained to a single atomic plane. The techniques described here are also applicable to other compositional phase boundaries such as III-V heterostructures.