This study investigates the feasibility of growing high quality columnar InAs/GaAsSb quantum dots (QDs) on a GaAs (1 0 0) substrate using a molecular beam epitaxial system. Structural and photoluminescence (PL) studies are conducted on vertically aligned, ten-period InAs quantum dot (QD) stacks with two different overgrown layer designs. Experimental results indicate an increased dot density of 5 x 10(10) cm(-2) with completely suppressed coalescences in vertically aligned InAs quantum dots capped by a GaAsSb layer. This finding demonstrates a columnar dot structure with an enhanced luminescent intensity, activation energy, and narrow spectral line width of 22 meV. (C) 2010 Elsevier B.V. All rights reserved.