Incorporation kinetics of rare‐earth elements (Er,Pr) in Si during solid source molecular beam epitaxy (MBE) is studied using secondary ion mass spectrometry. Pronounced surface segregation is consistently observed both for Er and Pr in normal MBE growth and their segregation tendencies are even stronger than those of typical dopants. Segregant‐assisted growth (SAG) using Sb was successful in significantly reducing the surface segregation of rare‐earth atoms, thereby opening the possibility of establishing layered structures in normal MBE. ©1995 American Institute of Physics.