Indium composition profiles in low density InAs/InGaAs quantum dot nanostructures

The two-dimensional quantum system composed by wetting layers and thin cladding layers in low density InAs/InGaAs quantum dot nanostructures was studied by structural and optical techniques. The indium composition and in-depth distribution outside the islands were obtained from XRD analysis of (004) diffraction profiles, by means of a best-fitting algorithm based on the dynamical theory. The formation of a InGaAs wetting layer with a maximum In fraction below 35% was inferred, and verified by TEM analysis at the nanoscale. On the basis of thicknesses and compositions of the layers as obtained by XRD, model calculations of quantum confined energy levels were carried out and a good agreement was found between the predicted wetting layer ground-state emission and the low temperature photoluminescence peak energy. This proves the validity of the proposed characterization method, based on non-destructive XRD experiments, as a powerful technique to investigate the indium composition profile in such complex quantum systems.