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Photoluminescence (PL) measurements performed in a series of InAs self-assembled quantum dot (QD) structures grown by molecular beam epitaxy (MBE) on GaAs (100) substrates using a two-stage "nucleation-augmented" growth method show that an InAs QD "nucleation" layer grown at a fast growth rate, followed by a slowly grown InAs "augmented" layer, dramatically increases the dot density and improves the PL intensity. Besides red-shift in peak wavelength, the PL intensity was found to increase as the growth rate of the InAs augmented layer was reduced. The increased PL intensity was due to a higher dot density arising from the nucleation layer and an improved optical quality caused by the growth interruption in the augmented layer.

Experimental data are presented on variations of the in-plane lattice constant of Ge and Si films in the course of the MBE film growth on the silicon (100) surface. The in-plane lattice constant of the silicon film is shown to alter as the film grows; the changes reflect the process of relaxation of elastic strains that result from the misfit of the germanium and silicon lattice constants. Due to the presence of germanium islands, a considerably thicker silicon film is required to provide the strain relaxation. The dependence of distortion penetration depth to the silicon film on the effective germanium film thickness is obtained. TEM studies indicate the vertical ordering of the germanium island layers when the thickness of the Si layer in between Ge layers is not sufficient to provide the full strain relaxation.