Bilayer quantum dots (BQDs) are interesting structures for long wavelength emission due to its ability to tune the areal density and dot size separately. However, wide implementation of BQDs is hindered by the complicated growth procedures, which involve two sets of growth rate and temperature for the respective QD layers. We had recently reported the optical properties of the BQDs grown at constant growth rate and temperature [Appl. Phys. Lett. 95 (2009) 181913]. In this work, we investigate the effects of GaAs spacer thickness and In(x)Ga(1-x)As strain-reducing layer on the structural and optical properties of such BQDs. (C) 2010 Elsevier B.V. All rights reserved.