The isolated threading dislocation

When considered in this framework, the resulting critical thickness condition is independent of any physical mechanism by which the interface misfit dislocation is actually formed in the system. This approach to critical thickness is an outgrowth of the pioneering work of Frank and Van der Merwe (1949) and the criterion was formulated in the way described here by Van der Merwe and van der Berg (1972). The most commonly observed mechanism for formation of misfit dislocations is through glide of a threading dislocation. In this section, the notion of critical thickness is re-examined on the basis of this mechanism. 

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Fig. 6.16. Glide speed of an isolated threading dislocation in a SiGe/Si(100) film versus inverse temperature from in situ transmission electron microscope observations. The slope of the line fitted to the data provides an estimate of the activation energy according to (6.29). Adapted from Nix et al. (1990).

When the threading segment is still far from the misfit dislocation in its path compared to h, its behavior is that of an isolated threading dislocation in the strained film. As it approaches the misfit dislocation, however, the shear stress acting on its glide plane is altered from the field... 

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