Photoluminescence and scanning electron microscopy have been used to study the growth of InAs quantum dots with InGaAsP barriers on (0 0 1) InP substrates for 1.55 mu m laser applications. The effect of growing quantum dots on a thin GaP layer as well as the use of a two step dot capping procedure was investigated, optimising for dot density, emission energy, and photoluminescence emission full-width half-maximum. It was found that the emission energy of a dot layer could be tuned around the important 1.55 mu m wavelength range while maintaining a high dot density and narrow dot size distribution, even when stacking multiple layers. An optimised dot structure was then used as the core of a single lateral mode laser diode demonstrating continuous wave operation at room temperature with a threshold of 25.9 mA and slope efficiency of 0.3 A/W. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.