D-A steps and 2D islands of double layer height in the SiGe(001) system

The surfaces of step graded, partially relaxed Si1-xGex/Si(001) buffers wer e studied by scanning tunneling microscopy. The surface slips along < 110 > forming the crosshatch pattern, consisting of bunches of D-A steps of doub le layer height. The D-A steps are present in regions of large surface grad ients close to the slips, as well as in planar regions between the slips. T hese regions are also characterized by the appearance of 2D islands of doub le layer height. The observations can be explained by assuming the strain d ue to the misfit dislocations to be locally anisotropic. Anisotropic misfit strain and efficient strain relaxation by the (2 X 8) Ge reconstruction we re identified as the main factors causing the unusual step structure.