A study was made of dislocation formation in the initial stages of coherency breakdown (the transition from coherent to incoherent epilayer growth). It was assumed that half-loop nucleation at the growing surface was the dominant route for spontaneous misfit dislocation generation in strained single hetero-epitaxial layers. On the basis of classical energy equilibrium theory, expressions were derived for the critical loop radius and critical nucleation energy for various habits. The dissociation of dislocations into partials was taken into account for layers that were grown under both compressive and tensile strain conditions. The stress dependence of the separation width between Shockley partials was also considered. Since the activation energy was too great for spontaneous half-loop nucleation at a flat surface, it was proposed that half-loop nucleation occurred at large surface steps which acted as stress concentrators. Due to the increase in stress there, the activation energy for half-loop nucleation was considerably decreased and the formation of misfit dislocations became more feasible.

The Film Surface as a Site for Spontaneous Nucleation of Dislocation Half-Loops in Strained Heteroepitaxial Systems. G.Wagner: Physica Status Solidi A, 1999, 173[2], 385-403