We report on the growth of quantum dot ͑QD͒ layers of InAsP alloys buried in GaAs by low-pressure metalorganic chemical vapor deposition. Ternary QDs were obtained by the addition of a PH 3 flux during the InAs QD growth, exhibiting recombination energies lying between those of InAs and InP QDs. The electronic properties of these QDs, as evaluated by photoluminescence spectroscopy, could be tailored by varying both the growth rate and the PH 3 flux for a constant AsH 3 flux. The morphology of these QDs was investigated by transmission electron microscopy from which the formation of an InAsP ternary alloy QDs was inferred. Based on electron microscopy results, the fundamental role of As incorporation on the morphology of and on the defect nucleation associated to InAsP QDs could be then evaluated. From this optical-structural combined analysis, we were able to identify the growth conditions that produce good quality InAsP QDs embedded in GaAs.