Hydrogen and oxygen doped FZ-Si samples with a high concentration of intrinsic defects and contaminant atoms can be considered as a model bulk system for the subsurface device-active region of contemporary Cz-Si wafers. We investigated the creation of vacancy related complexes and the carrier recombination process in such samples using infrared absorption and spin resonance measurement methods. Both the defect creation and carrier recombination processes were found to be affected by the presence of hydrogen or deuterium in the samples. Moreover, we detected an isotopic effect, namely, a significant difference in the influence of hydrogen and deuterium.