This paper presents a detailed morphological analysis of vertically strain-coupled InAs quantum dots with a fixed quaternary capping (In0.21Al0.21Ga0.58As) of 3 nm and a GaAs barrier ranging in thicknesses from 9 to 18 nm. The coupled heterostructures were studied using cross-sectional transmission electron microscopy and compared with uncoupled heterostructures with 2-nm quaternary capping and 50-nm GaAs capping thickness. Power-dependent photoluminescence spectra showed that a minimum capping of 9 nm produced a multimodal dot-size distribution. Increasing the capping from 9 to 18 nm reduced the vertical correlation, thus increasing the dot uniformity. Increasing the capping thickness reduced the coupling and increased the dot size. At a maximum capping (18nm) coupled quantum dots exhibit a bimodal dot-size distribution compared to the mono-modal distribution of the uncoupled quantum dots. The coupled samples demonstrated superior optical properties to uncoupled samples. © 2015 SPIE.