Nucleation and evolution of misfit dislocations in ZnSe/GaAs (001) heterostructures grown by low-pressure organometallic vapor phase epitaxy

Transmission electron microscopy and x-ray diffraction were used to study strain relaxation and the evolution of the dislocation structure in ZnSe epilayers grown by low-pressure organometallic vapor phase epitaxy on a (001) surface of semi-insulating GaAs. Before the ZnSe growth, the substrate surface was exposed to a flow of tertiarybutylarsine to promote an As-terminated surface. This surface treatment results in a low density of stacking faults; 60° misfit dislocations were observed at a layer thickness as low as 0.05 μm. This agrees well with the theoretical critical value for misfit dislocation formation in the ZnSe/GaAs system, but is much lower than experimental critical thicknesses reported earlier. Various mechanisms of misfit dislocation generation were observed at different growth stages. The evolution of the dislocation structure is discussed in relation with the morphology of the ZnSe layers.