A NEW SOURCE OF MISFIT DISLOCATIONS IN ZNTE GASB(001)/

Transmission electron microscopy is used to examine the nucleation of1 /2[110] misfit dislocations in epitaxial ZnTe/GaSb(001) films grown by molecular beam epitaxy. By studying films with ZnTe thicknesses close to the critical thickness for generation of misfit dislocations (abou t 0.2 mu M), it is shown that nucleation occurs at diamond-shaped loop s which lie on {111} planes and have 1/3[111] Frank-type Burgers vecto rs. Evidence is presented that these 'diamond defects', which are of v acancy type, undergo an unfaulting reaction in which a perfect disloca tion half-loop is generated on an intersecting {111} slip plane. Obser vations of the unfaulting process proceeding under the stimulus of the electron beam are illustrated. Once nucleated, subsequent slip and cr oss-slip of the threading segments of the new half-loop on the incline d {111} planes lead to interfacial 1/2[110] dislocations in 60 degrees orientation. It is suggested that diamond defects arise owing to a su persaturation of vacancies produced by reaction at the ZnTe-GaSb inter face, and that subsequent unfaulting is driven by the need to reduce t he dislocation loop energy. The significance of the mechanism, which o perates here at a lattice parameter mismatch of about 0.2%, for unders tanding misfit dislocation generation in other low-mismatch systems is discussed.