On the nature of cross-hatch patterns on compositionally graded Si1− x Ge x alloy layers

The effect of strain relaxation on the surface morphology of compositionally graded Si1−xGex layers grown at 550 °C has been investigated by a combination of transmission electron and atomic force microscopy. By annealing unrelaxed graded layers, we have found that shear displacements caused by dislocation glide roughen the surface dramatically. This effect is attributed to the formation of a network of dislocation clusters which give rise to the pronounced slip-band pattern on the surface of the graded layers. It is shown that the surface plastic displacements produced by such a network during growth of the graded layer contribute significantly to the formation of the cross-hatch patterns.