Investigation of the anisotropic strain relaxation in GaSb islands on GaP

Abstract

The strain relaxation at the initial stages of highly mismatched (11.8%) GaSb grown on a GaP substrate following a Ga-rich surface treatment by molecular beam epitaxy has been investigated. High resolution transmission electron microscopy and moiré fringe analysis were used to determine the relaxation state in these GaSb islands in the [110] and [1–10] directions. The measurements revealed an anisotropic strain relaxation in these two directions; there is a higher misfit strain relaxation along the [110] direction where the islands are elongated, which is in agreement with a higher density of misfit dislocations. By combining molecular dynamics simulations and TEM results, the anisotropy in the strain relaxation is shown to be related to the asymmetry in the formation of interface misfit dislocations. The P-core glide set 60° dislocations (α type) and the Ga-core shuffle set Lomer dislocations serve as the primary misfit dislocation which contributes to the strain relaxation in the (1–10) interface, and the Ga-core glide set 60° dislocations (β type) and the P-core shuffle set Lomer dislocations for the (110) interface, respectively. The lower formation energy and higher glide velocity of the P-core glide set 60° dislocations (α type) result in a higher line density and more uniform periodical distribution of the misfit dislocation in the (1–10) interface. The higher fraction of Lomer dislocations, which is related to the dislocation configuration stability and surface treatment, promotes a better strain relief in the (1–10) interface, with a corresponding elongation of islands in the [110] direction.