On the generation of a cross grid of extended screw-type misfit dislocations on the ZnS_xSe_1-x/GaAs interface

Abstract

New sources for heterogeneous nucleation of both (110) and (110) extended screw-type misfit dislocations to relax the lattice shear stress on the ZnS _x Se_1-x/GaAs interface have been observed for the first time. These are identified as Shockley partial dislocations originating at the area close to the ZnS _x Se_1-x/GaAs interface. The Shockley partials are formed for the accommodation of the stacking enors 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 ZnS _x Se_1-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 fildsubstrate interface and at the film surface. This process involves an increase in the length of the threading segments under the stress σ ∼ 1 × 10⁹ 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 filrdsubstrate 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 ZnS _x Se_1-x/GaAs interface. A (110) 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(121)-type and ^a/₆(211)-type toward the interface. On the other hand, a (110) 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 (121)-type and ^a/₆(21 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 (110) directions.