Direct measurement of composition of buried quantum dots using aberration-corrected scanning transmission electron microscopy

The authors present a direct method to quantitatively measure the indium composition of buried InAs quantum dots embedded in a GaAs matrix. In this method, spatially resolved electron-energy-loss spectroscopy combined with aberration-corrected scanning transmission electron microscopy at atomic resolution was employed to measure compositional profiles across the center of a quantum dot and the adjacent wetting layer. The size and shape of the quantum dots were determined using the Z contrast in high angle annular dark field images. A substantial enrichment in indium at the top of the quantum dots was identified, which is consistent with theoretical predictions.