Metastable InGaAs/GaAs multi-layer structures, grown onto GaAs substrates with a constant interfacial strain and with a number of periods ranging from 14 to 75, were studied by using high-resolution X-ray reciprocal space mapping, transmission electron microscopy and differential contrast microscopy. These techniques were used to monitor the magnitude of relaxation and the change in crystalline state from coherent so-called pseudomorphic growth, to a dislocated condition, as the number of periods increased. For 14 periods, the diffuse intensity which arose from the entire multi-layer structure region was due to periodic coherent crystallites. For 17 and 30 periods, the displacement fields around the active region changed to coherent random crystallites. For 50 periods, the displacement fields of overlapping dislocations (from relaxation of the random crystallites) caused an initial relaxation of the active region. For 75 periods, relaxation of the strained region became bi-modal and was characterized by overlapping dislocations which were caused by mosaic-block relaxation and periodically spaced misfit dislocations which were formed by 60º dislocations.

Morphology and Relaxation in InGaAs/GaAs Multi-Layer Structures. A.L.Gray, A.Stintz, K.J.Malloy, T.C.Newell, L.F.Lester: Journal of Crystal Growth, 2001, 222[4], 726-34