The off-lattice displacement of B atoms in B-doped Si induced by the irradiation with light ion beam at room temperature has been investigated. A proton beam with energy ranging from 300 to 1300 keV was used to irradiate the single crystal Si samples containing a 400 nm thick surface layer (grown by molecular beam epitaxy) uniformly doped with B at a concentration of 1 × 1020 B/cm3. Channelling analyses along the axis using the 11B(p, α)8Be reaction (at 650 keV proton energy) were used to detect the off-lattice displacements of B during irradiation. B is substitutional in the as-grown sample. During irradiation the normalized channelling yield of B χB increases with the ion fluence and saturates at a value χF smaller than unity, being this value independent of the energy of the irradiating beam. No change on the Si channelling yield was detected. The B displacement rate decreases with increasing the …