Dislocations and their dissociation in SixGe1 - xalloys

Abstract

The dissociation of dislocations in undeformed Si_xGe_{1 - 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=½ 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 Δ = 3.5 ± 1 nm for screw orientations to Δ = 6.2 ± 1 nm for edge orientations. The corresponding values for x = 0.5 were higher, with separations between Δ = 3.9 ± 1 nm and Δ = 6.9 ± 1 nm. Stacking-fault energies γ = 56 ± 8 mJ m⁻² for x = 0.05 and γ = 53 ± 8 mJ m⁻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.