In order to achieve wideband luminescence, ultrahigh density InAs quantum dots (QDs) were grown on GaAsSb buffer layers by molecular beam epitaxy under various growth conditions. Ultrahigh density of 3.8-5.2 x 10(11) cm(-2) and large size fluctuation were obtained. Photoluminescence (PL) spectra of ultrahigh density QD layers were changed by adjusting the growth conditions. Three ultrahigh density QD layers with different PL spectra were stacked on GaAs (001) substrate. The PL spectrum of edge emission revealed strong intensity and a broad linewidth of 194 nm. The presented QD structures are expected for development of wideband superluminescent diodes. (c) 2012 Elsevier B.V. All rights reserved.