DISLOCATIONS AND THEIR DISSOCIATION IN SIXGE1-X ALLOYS

The dissociation of dislocations in undeformed SixGe1-x crystals grown from the melt with low (x = 0.05) and high (x = 0.5) Si contents was investigated using the weak-beam electron microscopy technique. Dislocations with total Burgers vectors b = 1/2[110] and of various orientations were found to be dissociated into Shockley partials, separated by an intrinsic stacking fault on a {111} glide plane. Extended dislocation nodes were also observed. For x = 0.05 the dissociation widths of single dislocations ranged from DELTA = 3.5 +/- 1 nm for screw orientations to DELTA = 6.2 +/- 1 nm for edge orientations. The corresponding values for x = 0.5 were higher, with separations between DELTA = 3.9 +/- 1 nm and DELTA = 6.9 +/- 1 nm. Stacking-fault energies gamma = 56 +/- 8 mJm-2 for x = 0.05 and gamma = 53 +/- 8 mJm-2 for x = 0.5 were deduced from measurements of the dissociation widths as a function of dislocation orientation, using anisotropic elasticity theory. The results are compared with those of previous investigations on elemental Si and Ge.