An effective method for molecular beam epitaxial construction of metastable, pseudomorphic SnGe/Ge(001) heterostructures is presented. This method exploits a surfactant species, Bi, to alter Sn surface‐segregation kinetics. Using the x‐ray standing wave technique, we demonstrate not only that Bi segregates to the growth surface more strongly than Sn, but that it also dramatically suppresses the segregation mobility of Sn. The limited Sn diffusivity, which is believed to stem from the full coordination of subsurface Sn atoms, allows the epitaxy of well‐ordered, metastable SnGe heterostructures. ©1996 American Institute of Physics.