Substitutional impurities (B, Ga) in Si experienced an off-lattice displacement during ion-irradiation using a H+ or He+ beam at room temperature in random incidence. Samples were prepared by solid phase epitaxy (SPE) of pre-amorphized Si subsequently implanted with B and Ga at a concentration of about 1× 10 20 at. cm− 3 confined in a 300 nm thick surface region. The lattice location of impurities was performed by a channelling technique along different axes (,) using the 11 B (p, α) 8 Be reaction and standard RBS for B and Ga, respectively. The normalized channelling yield χ of the impurity signal increases with the ion fluence, indicating a progressive off-lattice displacement of the dopant during irradiation in random incidence, until it saturates at χ F< 1, suggesting a non-random displacement of the dopant. In particular, at saturation the off-lattice displacement of B and Ga was investigated by angular …