A transmission electron microscopic study was made of the step contrast in plan-view samples of Si1-xGex/Si(001) superlattices, where x was equal to 0.33. The samples were prepared by chemical or ion-beam back-thinning. It was shown that strong contrast arose where strained layers emerged at the surface; either at hillocks or pits. By combining diffraction contrast analysis of the step contrast, with convergent beam electron diffraction studies of the surface topology, it was shown that chemically-thinned samples had a terraced surface and that the step contrast was due mainly to the relaxation of exposed SiGe layers at relatively abrupt ledges. The results were used to demonstrate that misfit dislocations were located at SiGe/Si, and not at Si/SiGe interfaces.

Y.Atici, D.Cherns: Journal of Crystal Growth, 1995, 154[3-4], 262-8