The effects of relaxed InGaAs virtual substrates on the formation of self-assembled InAs quantum dots

Abstract

Self-assembled InAs quantum dots (QDs) are grown on InGaAs/GaAs virtual substrates (VS) by molecular beam epitaxy. By growing InAs QDs on partially relaxed InGaAs layers with different thicknesses, hence with varying degrees of relaxation, we obtain InAs QDs which are aligned or grouped into distinct units. It was found that growths of InAs QDs on these VS result in preferential alignment along [1 1 0] and [1 −1 0] directions, and the thicker the InGaAs relaxed layer the higher the chance that QDs coalesce into distinct ensembles of QDs. We attribute the results to the difference in the underlying surface undulation due to different degrees of VS relaxation and to strain asymmetries, as confirmed by atomic force microscopy and high-resolution x-ray diffraction. A schematic description of InAs QD growth on partially relaxed InGaAs layers is given.