The implantation behavior of Sb in silicon has been investigated by studying the orientation dependence of the backscattering yield of a 1.0-MeV helium beam. This orientation dependence ("channeling") provides quantitative information on the location of implanted atoms in the lattice and also on the amount of lattice disorder accompanying the implantation. The general principles of the channeling technique and the advantages of using a beam of He+ rather than H+ are discussed. Results for 25 °C and 450 °C implantations are presented and compared. The hot implant introduces very little lattice disorder, and a large fraction (up to 95%) of the Sb atoms is found on substitutional sites. In the 25 °C implants, however, a heavily damaged region is formed around the track of each implanted Sb. At doses greater than ~1014 ions/cm2, these damaged regions overlap to produce an essentially amorphous layer, which then requires an annealing temperature of ~650 °C to reorder the lattice and to achieve a high level of substitutional Sb. "Hot implant" studies have also been made for several other dopants—Ga, As, In, and Xe; however, unlike Sb, the substitutional level in all these cases never exceeded 60%. This unique behavior of Sb implants in silicon has also been found in a corresponding study of the electrical characteristics (Paper II). A preliminary investigation of boron-doped silicon, using the orientation dependence of 670-keV protons, indicates that substitutional boron atoms are removed from lattice sites by relatively small doses of energetic protons. This enhanced sensitivity to radiation does not occur for the Sb-doped samples.