New sources for the heterogeneous nucleation of both <110> and <1¯10> extended screw-type misfit dislocations, which relaxed lattice shear stresses at the interface, were observed for the first time here. These were identified as being Shockley partial dislocations which originated in the area close to the interface. The Shockley partials formed in order to accommodate the stacking errors which were produced during island coalescence. Electron beam-induced  in situ  heating studies were carried out in order to observe the dislocation generation mechanism. The results showed that the stress which existed in the ZnSSe films gave rise to bowing-out of the threading segments of the Shockley partials. The bowing resulted from the fact that the dislocations were pinned at the film/substrate interface and at the film surface. This process involved an increase in length of the threading segments under a stress of about 109dyne/cm2. With further accommodation of the lattice strain, the line tension of the bowing threading segments was relieved by the movement of the pinning points at the film surface; with gliding of the threading segments towards the film/substrate interface. This was accompanied by the movement of one or both of the pinned points at the film surface. Finally, a segment of extended screw-type dislocation was generated when the segments of the Shockley partials reached the ZnSSe/GaAs interface. A <110> extended screw-type interfacial dislocation was generated by gliding of the threading segments of the Shockley partials on (1¯11)-type planes with Burgers vectors of (a/6)<121>-type and (a/6)<21¯1>-type towards the interface. On the other hand, a <1¯10> extended screw-type interfacial dislocation was generated by the gliding of threading segments of the Shockley partials on (111)-type planes with Burgers vectors of (a/6)<1¯21>-type and (a/6)<2¯1¯1>-type towards the interface. Finally, shear stresses between the film and the substrate were relaxed by the generation of a grid of extended interfacial dislocations with screw components directed along the <110> and <1¯10> directions.

L.H.Kuo, L.Salamanca-Riba, G.Hofler, B.J.Wu: Philosophical Magazine A, 1995, 71[4], 883-99