Thicknesses and compositions of AlGaInAs-based layers grown by low-pressure metal-organic vapor-phase epitaxy (LP-MOVPE) in the regime of selective area growth (SAG) have been measured and calculated. In this study, we have grown InAs, GaAs and AlAs binary bulk layers on patterned InAs and GaAs substrates, respectively, in order to assess separately the vapor-phase diffusion (VPD) length (D/k) of indium, gallium and aluminum species. Special care has been taken in the evaluation of the Aluminum D/k ratio, on which little information was available. A 3D VPD model has been used to predict the composition and thickness profiles of various alloys. The calculated profiles have been compared to the experimental ones for GaInAs, AlInAs, AlGaInAs layers and GaAlAs layers deposited on patterned InP and GaAs substrates, respectively. The good agreement between modeling and experiment, together with the perfect selectivity obtained for all the different alloys, holds for the validity of the calculated D/k ratio of Al, Ga and In species. In MOVPE-SAG, the efficiency of a computational model is a key issue for the engineering of future SAG integrated optical devices. (c) 2006 Elsevier B.V. All rights reserved.