Multiple dislocation loops in linearly graded InxGa1−xAs (0≤x≤0.53) on GaAs and InxGa1−xP (0≤x≤0.32) on GaP

We report transmission electron microscopy studies of dislocation structures in two lattice-mismatched III-V systems, InxGa1−xAs (0≤x≤0.53)/GaAs and InxGa1−xP (0≤x≤0.32)/GaP, grown by gas-source molecular beam epitaxy. Multiple dislocation-loops, extending from within a linearly graded buffer layer to deep inside the substrate, were observed in both systems. All dislocations in each set of loops consisted of 60° dislocations with the same Burgers vector on a similar {111} glide plane. The density in the graded buffer and the substrate was estimated to be 2×109/cm2, and their appearance was associated with low threading dislocation densities and good optical quality in material grown on top of the buffer layer, InP/In0.53Ga0.47As on GaAs or In0.32Ga0.68P on GaP.