Direct determination of strain and composition in InGaAs nano-islands using anomalous grazing incidence x-ray diffraction

We present a structural study of uncapped InxGa1-xAs islands grown on GaAs (001) by molecular beam epitaxy (MBE) with a nominal concentration of x = 0.5. Surface-sensitive grazing incidence x-ray diffraction (GID) is applied to study shape, strain, and interdiffusion in these self-organised grown nanostructures. Contrast variation close to the K edge of As by anomalous GID at the (200) superstructure reflection enhances the chemical sensitivity of the measurement and allows for a direct determination of the InAs concentration as a function of the lateral strain in the quantum dots (QDs). The evaluation of intensity mappings recorded in reciprocal space close to the (200) reflection together with atomic force micrographs (AFM) is used to attribute the strain and the InAs concentration to a certain height in the quantum dots. Thereby, a three-dimensional model of the strain and interdiffusion profile of the InGaAs QDs is reconstructed. (C) 2004 Elsevier Ltd. All rights reserved.