It is found that O atoms segregate to the surface during Cu homoepitaxial growth on (Formula presented) to retain the (Formula presented) surface. The presence of an O adlayer on the Cu surface raises the barrier height for the surface diffusion of the Cu adatom and increases the transition temperature of the growth mode from step flow to layer by layer. The rate-determining step for the growth is the site exchange between O atoms and Cu adatoms. There exists a critical Cu deposition rate (Formula presented) above which the O atoms cannot exchange the site with Cu adatoms during growth. (Formula presented) obeys an Arrhenius relation. The activation energy for the site exchange is estimated at 0.66 eV. © 1997 The American Physical Society.