InAs quantum dots (QDs) are grown on InP (1 0 0) substrates by metalorganic vapor-phase epitaxy and the optical quality depending on the InP capping procedure is evaluated. The thickness of the low-temperature (Low-T) InP cap layer directly on the QDs is crucial for the QD photoluminescence (PL) peak wavelength and efficiency when followed by high-temperature capping. With increase of the Low-T cap layer thickness, the PL peak redshifts and the efficiency increases up to a thickness of 8 nm after which the PL peak wavelength stays constant and the efficiency strongly decreases. This behavior is attributed to the balance between stability of the QDs and defect diffusion toward the QDs. (C) 2010 Elsevier B.V. All rights reserved.