Transmission electron microscopy was used to investigate mechanisms of misfit strain relaxation in epilayers that were grown onto GaAs (¯1¯1¯1)B substrates which were misoriented by 2º towards [2¯1¯1]. It was found that relaxation was achieved via a triangular network of misfit dislocations that lay along the three <1¯10> directions near to the interface. However, the dislocation distribution was anisotropic; with a much higher density of dislocations lying parallel to the [0¯11] direction. A second relaxation mechanism was observed, which involved the formation of deformation twins. These nucleated at the epilayer surface and grew down into the epilayer; sometimes entering the underlying buffer layer. The twin formation was also anisotropic, with twins forming only on the (¯111)[211] system. The dislocation and twin anisotropy could not be explained by using Schmid-factor considerations, but was thought to be associated with the heterogeneous nucleation of dislocations at the [0¯11] surface steps that were caused by the misorientation. The critical layer thickness for the transmission electron microscopic observation of misfit dislocations in In0.25Ga0.75As (¯1¯1¯1)B epilayers was found to be between 15 and 25nm. This was the same range as that for (001) epilayers having the same composition, and was expected from theoretical considerations of the effects of orientation upon the elastic modulus and the strain-relieving component of the misfit-dislocation Burgers vector.

S.P.Edirisinghe, A.E.Staton-Bevan, R.Grey: Journal of Applied Physics, 1997, 82[10], 4870-6