The surfaces of step-graded partially relaxed SiGe/Si(001) buffers were studied by means of scanning tunnelling microscopy. The surface slips along <110> formed a crosshatch pattern which consisted of bunches of steps of double-layer height. The latter steps were present in regions of high surface gradient, close to the slips, as well as in planar regions between slips. These regions were also characterized by the appearance of 2-dimensional islands of double-layer height. The observations could be explained by assuming that the strain which was due to misfit dislocations was locally anisotropic. Anisotropic misfit strain, and efficient strain relaxation via (2 x 8) Ge reconstruction, were identified as being the main factors which caused the unusual step structure.

DA Steps and 2D Islands of Double Layer Height in the SiGe(001) System M.Kummer, B.Vögeli, T.Meyer, H.Von Känel: Physical Review Letters, 2000, 84[1], 107-10