Dislocation relaxation in InAs y P1− y films deposited onto (001) InP by gas-source molecular beam epitaxy

The strain relaxation of InAsyP1−y layers grown on (001) InP substrates by gas-source molecular beam epitaxy was examined using transmission electron microscopy (TEM) and cathodoluminescence (CL) imaging. InAsyP1−y films with a thickness of 190 Å were prepared, systematically varying the As content from y=0.30 and 0.77, corresponding to a lattice mismatch between 0.97% and 2.5%. Relaxation was anisotropic, with 60° misfit dislocations lying predominantly along [11̄0], with a much lower density of dislocations along [110]. For y≳0.48, CL and plan-view TEM observations show slip traces which make angles of about ±40° with the [11̄0] direction. These slip traces correspond to pure-screw dislocation segments (gliding on {111}) cross slipping to glide on planes approximately parallel to {011}.