Band structure and strain distribution of InAs quantum dots encapsulated in (Al)GaAs asymmetric matrixes

Abstract

The strain distribution and the electronic band structure of InAs quantum dots (QDs) embedded in asymmetrical (Al)GaAs barriers were studied by numerical analysis based on the finite element method. The outlines of the structures were designed considering experimental outcomes such as QDs morphology, wetting layer thickness, and the composition of the materials observed for the molecular beam epitaxial growth and capping of InAs/(Al)GaAs samples. The Al content in the AlGaAs alloy encapsulating material prompted variations on the island’s shape, so regular and truncated pyramidal QDs were simulated. According to the simulations, higher values of positive biaxial strain tensor εxx were obtained above the apex zone in pyramidal QDs as compared to truncated ones. The heavy hole and light hole bands intercalated relative positions along the internal QDs profile, a consequence of the compressive and tensile strain distribution inside the pyramidal QDs. The biaxial strain and the elastic energy analyzed above the apex zone and below the islands are important for the vertical correlation probability, and we found dependence on the shape of the nanostructure and the distance from the top of the islands to the surface spacer. Finally, those nanoislands for which the capping procedure did not change the geometry, showed a higher number of confined eigenstates, which is required for many optoelectronic applications.