Dopant surface segregation during molecular beam epitaxy (MBE) growth is a serious problem for controlling the doping profiles. To understand the segregation mechanism is essential. In this study, we report the B segregation ratio values, determined using concentration transient analysis based on secondary ion mass spectrometry (SIMS) measurements, for Si and SiGe, respectively. For a comparison, segregation ratio calculations based on a simplified two-site exchange model were performed. It is found that the surface segregation effects of B and Ge during MBE Si growth are interconnected, where the lattice strain likely plays an important role.