It was shown that models, which treated a semicircular dislocation loop expanding into a semi-infinite layer, had to be modified when an epilayer/substrate interface was involved. Two cases were considered here. One was that of a semicircular loop which expanded, from a free surface, into a free-standing strained film. The other was that of an identical semicircular loop which expanded, from a free surface, into a film that was strained by a substrate. In the case of the free-standing film, the loop was accommodated favorably (in terms of energy) if the film thickness was greater than a critical value. In the case of the epitaxial film, the loop reached the strained interface and expanded in the interface as a misfit dislocation if the film thickness was greater than a critical value. It was noted that, in most situations, the second critical value was smaller than the first. Associated with the critical values were energy barriers which had to be overcome if the loops were to exhibit the above behaviors. In general, the energy barrier for the second process was smaller than that for the first.

J.Zou, D.J.H.Cockayne: Journal of Applied Physics, 1996, 79[10], 7632-5