The incorporation mechanism of oxygen into MBE-grown AlGaAs layers was systematically studied by changing the growth temperature, growth rate, and AlAs mole fraction during growth. We found that segregation of oxygen atoms plays a very important role in oxygen incorporation. The molecular species on the surface also affected the incorporation and desorption of oxygen atoms. Oxygen atoms accumulate on the surface of a substrate due to surface segregation. The concentration of the accumulated oxygen atoms and the coefficient of surface segregation control the incorporation of oxygen atoms. These processes reasonably explain all of the particular characteristics observed in the oxygen incorporation into MBE-grown AlGaAs layers including the formation of peaks and dips in the profile and a lag time between the change of conditions and change of incorporation. (C) 2003 Elsevier Science B.V. All rights reserved.