Gallium doped Si films were epitaxially grown on Si(100) substrates using a partially ionized Ga molecular beam at various substrate temperatures ranging from 300 to 1000 K with incident Si and Ga beam fluxes of 5×1014 atoms s−1 cm−2, which corresponds to 0.1 nm/s assuming the sticking coefficient to be unity. The surface structure and the surface composition were observed by an in situ RHEED–AES system. Ga ionization produced no observable change in surface structure or surface composition as compared with Ga doping without ionization. However, an increase of the carrier concentration was observed by Ga doping with a partially ionized molecular beam under the following ionization condition: an ion energy of 180 eV with 5% Ga ionization. Moveover, the lowering of the epitaxial temperature was observed using a partially ionized Si molecular beam under the ionization conditions: an ion energy ranging from 30 to 180 eV with ≲7% Si ionization.