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

Abstract

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·b = 0 invisibility criterion was not successful in the unambiguous determination of the Burgers vectors. As an alternative method, the symmetry property of dislocation images was used. These are symmetrical across the dislocation line for the g·b = 0 case but are asymmetrical for the g·b ≠ 0 case. This method was found to be particularly useful for the Burgers vector determination of a dislocation sloping through a foil specimen. Special care was however needed for a dislocation lying parallel to the foil plane, in which case the symmetry property of the dislocation images is not immediately obvious. Contrast experiments using various two-beam conditions have shown that the Burgers vector of the V-shaped dislocations is a/2[110] and the presence of the string residual contrast for the g·b = 0 case is due to the large |g·b × u| values.