The present extensive systematic study of defect introduction rates as a function of boron, gallium, oxygen, and carbon concentrations by means of deep level transient spectroscopy has drawn a quite complete picture towards the identification of the dominant radiation-induced defects in Si. The radiation-induced defect EV+0.36 eV has been identified as Ci–Oi complexes. The absence of an EC-0.18 eV complex center in gallium-doped samples and the linear dependence of its introduction rates on both the boron and oxygen content fixed its identification as the Bi–Oi complex in boron-doped Si. One of the technologically important results of present study is that the gallium appears to strongly suppress the radiation induced defects, especially hole level EV+0.36 eV (Ci–Oi), which is thought to act as a recombination center as well as the dominant compensating center at EC-0.18 eV (Bi–Oi). As a result, the effects of lifetime degradation and carrier removal could be partially offset to higher radiation fluences by using Ga as a dopant instead of boron in Si space solar cells. The anneal out of the new hole level EV+0.18 eV in gallium-doped samples at around 350 °C, together with recovery of free carrier concentration, suggests that this level may act as a donor-like center which compensates free carrier concentration in gallium-doped Si. © 2001 American Institute of Physics.