<title>Formation of screw-type misfit dislocations on the ZnSxSe1-x/GaAs interface</title>

Abstract

New sources for heterogeneous nucleation of both &lt;$110&gt; and &lt;110&gt; extended screw-type misfit dislocations to relax the lattice shear stress on the ZnS<SUB>x</SUB>Se<SUB>1-x</SUB>/GaAs interface has been observed for the first time. These are identified as Shockley partial dislocations originating in areas close to the ZnS<SUB>x</SUB>Se<SUB>1-x</SUB>/GaAs interface. The Shockley partials form to accommodate 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 (sigma) approximately equals 1 X 10<SUP>9</SUP> dyne/cm<SUP>2</SUP> stored in the ZnS<SUB>x</SUB>Se<SUB>1-x</SUB> films gives rise to bowing of the threading segments of the Shockley partials. The bowing result 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 treading segments under the stress. With further accommodation of the lattice strain, the line tension of the bowing threading segments is relieved by the movement of the pinning points at the film surface accompanied by gliding of the threading segments toward the film/substrate interface. This process takes place by the movement of either 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<SUB>x</SUB>Se<SUB>1-x</SUB>/GaAs interface. A &lt;110&gt; extended screw-type interfacial dislocation is generated by gliding of the threading segments of the Shockley partials on (111)-type planes with Burger vectors b equals a/6&lt;121&gt;-type and a/6&lt;211&gt;-type toward the interface. On the other hand, a &lt;110&gt; extended screw-type interfacial dislocation is generated by gliding of the threading segments of the Shockley partials on (111)- type planes with Burger vectors b equals a/6&lt;121&gt;-type and a/6&lt;211&gt;-type toward the interface. Finally, the shear stress between film and substrate is relaxed by the generation of a grid of extended interfacial dislocations with screw components along the &lt;110&gt; and &lt;110&gt; directions.