On the Reduction of the Critical Thickness in InxGa1-xAs Quantum Well Layers Grown on Vicinal GaAs Substrates

By comparison with equivalent layers grown on untilted substrates a reduction of the critical thickness in InGaAs quantum wells grown on vicinal GaAs substrates by the emission of half loops in the secondary a/2<110>(110) glide system, leading to the formation of <010> aligned misfit dislocations, has been found. The layers grown on vicinal substrates also contained regularly spaced compositional macrosteps. As the propagation of dislocations in the a/2<110>(110) glide system, and associated reduction of the critical thickness, requires high strains because of the high Peierls friction, it is argued that the nucleation of the half loops occurred at the observed compositional macrosteps as they can act as sites of enhanced strain concentration. For layers grown on untilted substrates only the usual a/2<110>(111) glide system was observed.