  The critical thickness constitutes a vital parameter in heterostructure
epitaxy engineering as it determines the limit where crystal coherency is lost.
By finite element modeling of the total strain relaxation in finite size
heterostructure nanowires, we show that the equilibrium configuration changes
abruptly at the critical thickness from a fully elastically strained structure
to a structure with a network of MDs. We show how the interdependent MD
relaxation changes as a function of the lattice mismatch. These findings
suggest that a collective formation of MDs takes place when the growing
heterostructure layer exceeds the critical thickness.
