We systematically studied on ion dose, energy, and species dependencies of strain relaxation ratios for SiGe buffer layers fabricated by ion implantation technique where the epitaxial growth of SiGe layers was carried out on Si or Ar ion preimplanted Si substrates. For Si+ implantation, we found that there was an optimal ion-implantation condition to effectively enhance strain relaxation of the SiGe layers, that is, relaxation ratios increased with the ion dose but reduced remarkably when it exceeded a certain critical dose (∼1×1015 cm-2). The drop of relaxation also occurred as the implantation energy increased. Based on simulations and transmission electron microscopy (TEM) observations, it was concluded that end-of-range (EOR) defects generated by Si+ implantation crucially caused formation of high-density misfit dislocations at the heterointerface, and the observed complicated results were well understood in terms of the position of EOR defects from the heterointerface. We confirmed this conclusion by observing that relaxation ratios monotonically increased as the EOR defects position from the heterointerface was decreased by means of surface etching. On the other hand, for Ar+ implantation, relaxation ratios were seen to increase monotonically with the increase in ion dose without any drop even in the high dose region. Void-related defects formed around projected range of ion implantation were thought to dominate strain relaxation of the SiGe layers differently from Si+ implantation case. This difference in the relaxation mechanism between Si+ and Ar+ implantation was also found in and confirmed by TEM and atomic force - - microscopy observations.