Evolution of Kinetically Limited Lattice Relaxation and Threading Dislocations in Temperature-Graded ZnSe/GaAs (001) Metamorphic Heterostructures.

We have investigated the evolution of strain and threading dislocation density in metamorphic temperature-graded ZnSe buffer layers. Mismatched semiconductor heterostructures may be designed to take advantage of temperature grading to allow control over the relaxation process. To study temperature grading, we have applied a plastic flow model which predicts nonequilibrium strain relaxation as well as misfit and threading dislocation densities by accounting for the time evolution of kinetically limited and equilibrium strain relaxation, thermal activation of glide, and misfit-threading dislocation interactions. We considered ZnSe/GaAs (001) heterostructures comprising a convex-down (type A), linear (type B), and convex-up (type C) temperature grading profile. The thermal budget available for relaxation in these types of structures is controlled by the temperature grading profile, which consists of combinations of linear ramp-down and/or constant temperature growth; the temperature is varied from T (400°C to 600°C) at the substrate interface to T = 300°C at the surface. We show that structures with a higher thermal budget exhibit a greater extent of relaxation (lower strains). At lower thicknesses, the dislocation density is dominated by the extent of relaxation, whereas at greater thicknesses, it is controlled by annihilation and coalescence mechanisms. [ABSTRACT FROM AUTHOR]