InGaP/GaAs is an attractive material system to realize ultra fast electronic devices and optical devices. Fabrication of a monolayer abrupt hetero-interface by metal organic vapor phase epitaxy (MOVPE) is difficult, however, due to the rapid As/P exchange on the growth surface. Here, adsorption/desorption kinetics of group-V atoms on GaAs surface during a gas-switching sequence to form InGaP/GaAs structure was studied by using in situ kinetic ellipsometry. The in situ monitoring of the GaAs dielectric constant revealed that P diffuses easily and quickly into GaAs and that excess As adsorbed on the GaAs surface in MOVPE is difficult to desorb during the gas-switching sequence. Based on these results, we developed a novel gas-switching sequence in which an additional TMGa supply and a group-III pre-flow (GIIIP) were introduced for the first time. By optimizing this GIIIP sequence (i.e., by controlling the additional TMGa supply time), we successfully fabricated an abrupt interface of InGaP on GaAs. The effectiveness of this sequence was confirmed based on photo-luminescence measurements. (c) 2006 Elsevier B.V. All rights reserved.