DISLOCATIONS IN GaAs.

Bright-field and weak-beam dark-field microscopy techniques have been used to study straight dislocations and faulted dipoles in semi-insulating GaAs and in both MBE- and OMVPE-grown Al//xGa//1// minus //xAs/GaAs heterojunctions. The low temperature, high-stress deformation results in a dislocation configuration where the dislocations lie along their Peierls valleys. Using TEM specimens prepared from such deformed material, the mobility of alpha and beta dislocations, the asymmetry of motion of 60 degree - beta -dislocations and screw dislocations could be observed directly. High temperature deformation (425 degree C) results in the formation of less well-defined dislocation and many dislocation dipoles, some of which are found to be faulted dipoles. A cross-sectional TEM technique allowing the direct study of screw dislocation motion through epilayers is presented. This technique showed that dislocation dipoles can be formed at heterojunctions as a result of dislocation glide.