Vertical composition gradient in InGaAs∕GaAs alloy quantum dots as revealed by high-resolution x-ray diffraction

Shape and composition profiles of self-organized In0.6Ga0.4As∕GaAs quantum dots (QDs) were investigated using diffuse x-ray scattering of a fivefold QD stack. To reveal the QD morphology, numerical scattering simulations of QDs with different morphologies were performed based on three-dimensional strain fields calculated by the finite element methods. Comparing our simulations to the data, we proved that the In concentration increases from the wetting layer to the top of the quantum dots. Moreover, we conclude that the In concentration of the wetting layers is significantly lower than the average value in the QDs.