Investigation of shape, strain, and interdiffusion in $InGaAs$ quantum rings using grazing incidence x-ray diffraction Available to Purchase

The formation of nanoscopic $InGaAs$ ring structures on a $GaAs(001)$ substrate takes place when $InAs$ quantum dots, grown by Stranski-Krastanov self-organization, are covered by a thin layer of $GaAs$⁠. The shape transformation into rings is governed by strain, diffusion, and surface tension, physical parameters which are of importance to monitor the magneto-optical and electronic properties of the rings. In this work we report on the characterization of morphology and structure of the rings in three dimensions (such as strain and chemical composition). To this end we apply grazing incidence small angle x-ray scattering (GISAXS) and grazing incidence diffraction (GID). From GISAXS the shape is 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 is derived from intensity mappings in reciprocal space close to the $(220)$ and $(22¯0)$ reflections done in the surface sensitive GID geometry. From a comparison of the intensity maps with finite-element model calculations the $InGaAs$ interdiffusion profile in the ring is determined. It strongly depends on the crystallographic orientation. In the ring we find a maximum $InAs$ concentration of more than 80% along $[11¯0]$⁠, while along $[110]$ it is below 20%. This results from the preferred diffusion of $InAs$ along $[11¯0]$⁠.