Morphological and geometric phase analysis of GaSb/GaAs quantum dots grown at atmospheric pressure using MOVPE

The geometric phase, surface structure and chemical interchange between GaAs and GaSb regions in GaSb/GaAs quantum dot (QD) structures which were deposited at atmospheric pressure (AP) using metalorganic vapor phase epitaxy (MOVPE) have been analysed using scanning probe microscopy (SPM), photoluminescence spectroscopy (PL) and transmission electron microscopy (TEM). A non-arbitrary quantification procedure of an averaged electron energy-loss spectroscopy (EELS) spectrum, extracted from an area of interest on the sample was used for elemental mapping of individual constituents in the quantum dots (QDs) and the surrounding area, while PL measurements where used to optically confirm the wetting layer and the QDs. The uncapped sample consists of uniform but densely populated dots with a dome-like structure, a height of ~ 4.5 nm and an average base length of 42 nm. Voids were visible in some of the dots as a result of the diffusion of Sb away from the dot region into the GaAs cap and buffer. Segregation of Sb adatoms tends to occur when Sb concentration is sufficiently high. The compact capped dots retained similar dimensions as the uncapped dots and revealed a higher concentration of Sb at the centre, with arsenic (As) intermixed at the periphery. Estimation of lattice strain within the compact dot indicates that the strain was distributed inhomogenously throughout the dot region.