Compositional characterization of GaAs/GaAsSb nanowires by quantitative HAADF-STEM

► Sb concentration in axial GaAsSb inserts of GaAs nanowires was studied using quantitative HAADF-STEM. ► The Sb distribution was analysed in both axial and radial directions. ► Sb concentration builds up gradually along the insert and drops either gradually or abruptly, depending on the growth conditions. ► Sb concentration is reduced towards the outer surfaces of the nanowires. ► Including the static atomic displacements in the image simulations was crucial for correct compositional analysis of GaAsSb. The Sb concentration in axial GaAs1−xSbx inserts of otherwise pure GaAs nanowires has been investigated with quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The Sb concentration was quantified by comparing the experimental image intensities normalized to the incident beam intensity with intensities simulated with a frozen lattice multislice approach. Including static atomic displacements in the simulations was found to be crucial for correct compositional analysis of GaAs1−xSbx. HAADF intensities of individual nanowires were analysed both across the nanowires, exploiting their hexagonal cross-sectional shape, and along the evenly thick central part of the nanowires. From the cross-sectional intensity profiles, a decrease in the Sb concentration towards the nanowire outer surfaces was found. The longitudinal intensity profiles revealed a gradual build-up of Sb in the insert. The decrease of the Sb concentration towards the upper interface was either gradual or abrupt, depending on the growth routine chosen. The compositional analysis with quantitative HAADF-STEM was verified by energy dispersive X-ray spectroscopy.