Burgers vector determination of V-shaped dislocations in InGaAs layers grown on (001) InP substrates.

The nature of V-shaped dislocations in InGaAs layers grown by molecular beam epitaxy on (001) InP substrates was studied using transmission electron microscopy. Due to the presence of strong residual contrast associated with these dislocations, the usual g(bar).b(bar) = 0 invisibility criteria was not successful in the unambiguous determination of the Burgers vectors. As an alternate method, we used the symmetry property of dislocation images; dislocation images are symmetrical across the dislocation line for the g(bar).b(bar) = 0 case but are asymmetrical for the g(bar).b(bar) not = 0 case. This method was found to be particularly useful for the Burgers vector determination of a dislocation sloping through a foil specimen. In combining the asymmetry property of the dislocation contrast with the g(bar).b(bar) = 0 invisibility criteria, contrast experiments using various two-beam conditions on both (001) horizontal and (110) cross section have shown that the V-shaped dislocations are of an unusual type dislocation in this material. They lie on the {110} planes and their Burgers vectors are of pure edge type with b(bar) = a/2. The presence of the strong residual contrast for the g(bar).b(bar) = 0 case is due to the large g(bar).b(bar)xu(bar) values.