Dislocations in MBE-grown ZnSe/GaAs(001) epitaxial layers

We report on dislocation densities in MBE grown ZnSe/GaAs/GaAs heterostructures of different epilayer thickness determined by high-resolution X-ray diffraction (HRXD), transmission electron microscopy (TEM) and etch-pit density (EPD) direct determination. We observed three regimes of dislocation generation. The first regime is present for samples of sub-critical thickness, where only stacking faults (SF) are present. SF formation depends on the conditions of substrate preparation and initial growth conditions. The second regime exists for samples with layer thickness greater than the critical thickness and thinner than a threshold thickness h(t) congruent to 0.3 mu m, where a large amount of misfit (MF) dislocations are generated as consequence of SF reactions. We observe by TEM that the formation onset of MF dislocations starts at a critical thickness h(c) similar to 0.12 mu m. The third regime, starts for layer thickness greater than h(t). In this regime the formation of dislocations is substantially slowed down and the dislocation density follows a 1/h dependence as predicted by the glide model.