Room-temperature B off-lattice displacement and electrical deactivation induced by H and He implantation

Substitutional boron atoms in silicon experience an off-lattice displacement during ion-irradiation with energetic light ions at room temperature. The off-lattice displacement rate has been measured in a B-doped Si by channelling analyses using nuclear reaction (650 keV proton beam, 11B(p,α)8Be). The normalized channeling yield χ of B increases with the ion fluence until it saturates at a value smaller than 1. This indicates that B is not totally displaced in a random site. The carrier concentration in layer, measured by Van Der Pauw and Hall effect techniques, decreases during irradiation until complete de-activation of B occurs. The comparison of electrical and structural analyses is consistent with the formation of small, not electrically active B complexes stable at room temperature in presence of an excess of point defects.