We have recently reported the annealing and electrical properties of three new families (N1, N2 and N3) of vacancy complexes introduced in 1 keV He-, Ne- and Ar-ion bombarded nSi. In this paper we have employed deep level transient spectroscopy to investigate the ion mass, fluence and energy dependence of the introduction of N1 -defects. We observed an increase in the intensity of Ni -defects with increasing mass of bombarding ions for a fluence of 1×1012cm−2and flux of 1×1011cm−2s−1, which we have correlated with the mass dependence of nuclear energy deposition. The ratio of the intensities of Ni-defects to VO-center, [N1]/[VO], increased by ∼5 when bombarding with Ar- compared to He-ions. Increasing the Ar-ion fluence from 1×1012cm−2to l×1014cm−2for a flux of 5×1010 cm−2s−;1increased the intensity of N1-defects by ∼20 times, while [N1]/[VO] increased by a factor ∼2.3. N1-defects were not created by 5.4 MeV alpha-particle irradiation, but were present in varying relative concentrations in 1 to 150 keV He-ion bombarded n-Si.