Strain assisted inter-diffusion in GaN/AlN quantum dots

Abstract

The structural and optical properties of high temperature-annealed superlattices of GaN quantum dots embedded in AlN barrier have been studied by a combination of X-ray techniques (reciprocal space mapping, multiwavelength anomalous diffraction, and diffraction anomalous fine structure), high resolution transmission electron microscopy, and photoluminescence spectroscopy. Taking advantage of the disentangling of the chemical and structural information provided by the simultaneous use of X-ray absorption and diffraction data obtained in a synchrotron environment, we provide quantitative determination of strain and composition for each different region of the nanostructures. Eventually, it is shown that strain driven dot/barrier intermixing is present, mostly on top of the dots. These observations have been confirmed by high resolution electron microscopy. A blue shift of photoluminescence peak has been furthermore observed and assigned to GaN/AlN intermixing suggesting a new path for engineering the emission wavelength of such heterostructures.