Reflection high-energy electron diffraction measurements of the critical thickness θcrit for quantum dot (QD) formation have been used to quantify the effects of indium segregation and strain on the growth of bilayer InAsGaAs(001) QD structures. These are not straightforward to deconvolute, because of the complex issues that arise during the growth and capping of the QDs. Segregation and out diffusion of In from buried QDs are shown to occur for GaAs thicknesses up to 6nm at 580°C. The existence of a floating In adlayer on the surface of the GaAs-capping layer as a result of In segregation is apparent at much lower substrate temperatures (510°C). The relative contribution of both segregation and strain on the reduction of θcrit during the growth of a second InAs layer is assessed. Compared with segregation, strain from the buried QDs can be measured through significantly larger capping thicknesses (30nm) under these conditions.

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