The codiffusion of Ge with dopant atoms (boron or arsenic) into Si substrates is analyzed using secondary ion mass spectroscopy. While earlier studies have focused on the diffusion of dopants across deposited Si1-xGex films or on diffusion phenomena at in situ doped Si1-xGex/Si interfaces, this paper reports on the codiffusion of Ge and implanted dopant atoms into Si substrates resulting in the in situ formation of heavily doped Si1-xGex/Si heterojunctions. The presence of dopants is seen to significantly enhance interfacial Si-Ge interdiffusion. The differences are discussed in light of the different diffusion mechanisms prevalent in the various heterojunction systems (undoped Ge/Si. p(+) Ge/Si, and n(+) Ge/Si).