Epilayers of CdTe were grown onto (001) GaAs and were studied by using transmission electron microscopy. The overall dislocation reduction effect, as deduced from plan-view measurements, was found to be 2.5 times; with the bending of threading dislocations occurring largely at the top and bottom layers in each of two built-in CdTe/CdZnTe superlattices. However, it was found that a large number of threading dislocations in the epilayer existed in the form of dipole pairs. In particular, long straight dislocations which originated in the interface region were almost always close dipole pairs, with typical spacings of less than 10nm between the components. A model was proposed which explained the formation of long straight dislocation dipoles in the early stages of growth. It was proposed that dislocations with opposite Burgers vectors, gliding on parallel {111} planes, interacted to form close dipole pairs which were elongated in <112> directions. It was shown that the pairing of dislocations in this manner reduced the effectiveness of superlattice layers in dislocation filtering. Also, the dislocations in dipole pairs were frequently found to be dissociated into 2 partial dislocations. Such effects complicated the dynamics of dislocations in CdTe/GaAs and were expected to place great limitations on the ability of superlattices to remove threading dislocations from these epilayers.

A.Hobbs, O.Ueda, I.Sugiyama, H.Takigawa: Journal of Crystal Growth, 1992, 117, 475-9