We reported the growth of asymmetric InAs bilayer quantum dots (QD) on GaAs substrate by molecular beam epitaxy. A combination of different InAs growth rates (GR) for the two QD layers was used, respectively, to increase QD density and extend photoluminescence (PL) emission wavelength. A high GR used for the first layer guarantees a high QD density; while a low GR used for the second layer helps to extend the PL emission wavelength due to the dot size increase, which was confirmed by transmission electron microscopy and PL measurements. It was found that this kind of QDs is very sensitive to post-growth annealing procedure due to the dot size increase. By appropriately choosing the growth parameters, InAs bilayer QD laser diodes embedded in a conventional AlGaAs/ GaAs waveguide structure were demonstrated. The devices yielded the lowest ever reported threshold current density of 134 A/cm(2) in the range of 1.5 mu m wavelength for GaAs-based lasers. (c) 2006 Elsevier B.V. All rights reserved.