Accommodation of lattice misfit in Si 1− xGe x/Si heterostructures

Abstract

Strain accomodation by formation of misfit dislocations for Si 1 - x Ge x epitaxial layers on Si(001) is described, based on transmission electron microscopy studies. Misfit dislocations introduced at the interfaces for x ≤ 0.5 are inclined 60°-type dislocations. These dislocations nucleate at the surface, and then expand to the interface by glide processes. The generated dislocations show an equilateral triangular V-shape. Energy considerations show that this type of V-shaped dislocation is generated more favorably than the semicircular one generally assumed in previous theories for predicting the critical thickness of this system. The misfit dislocation densities increase with Ge composition and thickness as a result of the Hagen-Strunk multiplication mechanism. The analyses show that the misfit dislocations which possibly nucleate at the surface have a Burgers vector of 1 2 a 0[011], 1 2 a 0[0 1 1], 1 2 a 0[101] or 1 2 a 0[ 1 01], where a 0 represents the lattice parameter of the epitaxial layer, and that these misfit dislocations coexist along orthogonal [110] and [ 1 10] directions. Thus, Hagen-Strunk multiplications necessarily occur. Finally, problems concerning the critical thickness of this system are discussed based on these findings.