On the use of total reflection x-ray topography for the observation of misfit dislocation strain at the surface of a Si/Ge–Si heterostructure

Abstract

Synchrotron x-ray topography was used in total reflection topography (TRT) mode to observe strain-induced surface bumps due to the presence of underlying misfit dislocations in strained-layer SiGe on Si epitaxial heterostructures. In these experiments, the x rays approached the sample surfaces at grazing incident angles below the critical angles for total external reflection for a number of reflections, and hence, surface strain features nominally less than a few tens of angstro/ms from the sample surface have been observed. These are similar to the surface bumpiness observed by atomic force microscopy, albeit on a much larger lateral length scale. The fact that TRT mode images were taken was confirmed by the observation of conventional backreflection topographic images of misfit dislocations in all samples when the grazing incidence angle became greater than the critical angle.