Amorphous, polycrystalline, and epitaxial thin films of Si and Ge have been grown by ion beam deposition (IBD) under ultrahigh‐vacuum conditions. IBD involves the direct deposition of ions onto single‐crystal substrates from mass‐ and energy‐analyzed beams with energies of 10 to 200 eV. The IBD films were characterized by Rutherford backscattering, ion channeling, cross‐section transmission electron microscopy, and x‐ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning were studied. Differences in the formation of epitaxial thin films on p‐ and n‐type Si substrates were observed with n− Si showing better epitaxy at low temperatures. Epitaxial overlayers which showed good minimum yields by ion channeling (3%–4%) have been produced at temperatures as low as 375 °C for Ge on Ge(100) and Si on Si(100).