ON THE GENERATION OF A CROSS GRID OF EXTENDED SCREW-TYPE MISFIT DISLOCATIONS ON THE ZNSXSE1-X/GAAS INTERFACE

New sources for heterogeneous nucleation of both [110] and [1 ($) over bar 10] extended screw-type misfit dislocations to relax the lattice shear stress on the ZnSxSe1-x/GaAs interface have been observed for the first time. These are identified as Shockley partial dislocations originating at the area close to the ZnSxSe1-x/GaAs interface. The Shockley partials are formed for the accommodation of the stacking errors produced upon island coalescence. In-situ electron beam-induced heating studies were carried out to observe the dislocation generation mechanism in the films. Our results show that the stress existing in the ZnSxSe1-x films gives rise to bowing of the threading segments of the Shockley partials. The bowing results from the fact that the dislocations are pinned at the film/substrate interface and at the film surface. This process involves an increase in the length of the threading segments under the stress sigma similar to 1 x 10(9) dyne cm(-2). With further accommodation of the lattice strain, the line tension of the bowing threading segments is relived by the movement of the pinning points at the film surface with gliding of the threading segments toward the film/substrate interface. This process is accompanied by the movement of one or both of the pinned points at the film surface. Finally, a segment of extended screw-type dislocation is generated when the segments of the Shockley partials reach the ZnSxSe1-x/GaAs interface. A [110] extended screw-type interfacial dislocation is generated by gliding of the threading segments of the Shockley partials on [1 ($) over bar 11]-type planes with Burgers vectors b = a/6[1 ($) over bar 21]-type and a/6[2 ($) over bar 1 ($) over bar 1]-type toward the interface. On the other hand, a [1 ($) over bar 10] extended screw-type interfacial dislocation is generated by gliding of the threading segments of the Shockley partials on (111)-type planes with Burgers vectors b = a/6[1 ($) over bar 21]-type and a/6[2 ($) over bar 1 ($) over bar 1]-type toward the interface. Finally, the shear stress between the film and substrate is relaxed by the generation of a grid of extended interfacial dislocations with screw components along the [110] and [1 ($) over bar 10] directions.