The formation of nanoscopic InGaAs ring structures on a GaAs(001) substrate takes place when InAs quantum dots, grown by Stranski-Krastanov self-organization, were covered by a thin layer of GaAs. The shape transformation into rings was governed by strain, diffusion, and surface tension, physical parameters which were of importance to monitor the magneto-optical and electronic properties of the rings. The characterization of the morphology and structure of the rings in three dimensions (such as strain and chemical composition) was studied. For this, grazing incidence small angle X-ray scattering (GISAXS) and grazing incidence diffraction were used. From GISAXS the shape was found to be of circular symmetry with an average outer radius of 26nm, a height of about 1.5nm, and a hole in the middle, in good agreement with atomic force microscopy measurements. Information about strain and interdiffusion was derived from intensity mappings in reciprocal space close to the (220) and (2¯20) reflections done in the surface sensitive grazing incidence diffraction geometry. From a comparison of the intensity maps with finite-element model calculations the InGaAs interdiffusion profile in the ring was determined. It strongly depends on the crystallographic orientation. In the ring, a maximum InAs concentration of more than 80% along [1¯10] was found while, along [110], it was below 20%. This results from the preferred diffusion of InAs along [1¯10].

Investigation of Shape, Strain and Interdiffusion in InGaAs Quantum Rings Using Grazing Incidence X-Ray Diffraction. M.Sztucki, T.H.Metzger, V.Chamard, A.Hesse, V.Holý: Journal of Applied Physics, 2006, 99[3], 033519 (9pp)