An ion-beam mixing technique is used to fabricate ultrashallow p(+)/n junctions. In this method, a thin boron layer is first sputter deposited onto the Si wafer surface. Then a 10-40 keV Ge ion beam or -3 kV Ar plasma source ion implantation (PSII) is used to knock the boron atoms into the Si substrate by means of ion-beam mixing. For the thin (0.7 nm) boron layers used in this effort, a selective etch for the removal of boron is unnecessary. Sub-100 nm p(+)/n junctions have been realized with this method. Numerical simulations, performed to predict the recoiled boron profiles, show good agreement between the simulated and measured data.