Apparent critical layer thickness in ZnSe/GaAs (001) heterostructures and the role of finite experimental resolution

The critical layer thickness h c for the onset of lattice relaxation has important implications for the design of pseudomorphic and metamorphic II–VI device structures on lattice-mismatched substrates. Several theoretical models have been developed for the critical layer thickness, including the well-known force-balance model of Matthews and Blakeslee [J. Cryst. Growth 27, 188 (1974)]. Experimentally measured critical layer thicknesses in ZnSe/GaAs (001) heterostructures are often at variance with one another as well as the Matthews and Blakeslee model. By assuming that the lattice relaxation is a fixed fraction of the equilibrium relaxation (constant γ / γ e q ), Fritz [Appl. Phys. Lett. 51, 1080 (1987)] has shown that the measured h c may be much larger than the equilibrium value when using a finite experimental resolution. However, the assumption of constant fractional relaxation is not applicable to any heterostructure exhibiting kinetically limited lattice relaxation. In order to reconcile the conflicting results for II–VI materials, the authors applied a general dislocation flow model to determine the apparent critical layer thickness as a function of the experimental resolution for ZnSe/GaAs (001) heterostructures. The authors show that the Matthews and Blakeslee model is consistent with several measured values of h c once the kinetically limited relaxation and finite experimental strain resolution are taken into account.