We have calculated the nucleation energy barrier of voids and vacancy(V)type dislocation loops in Si underV-supersaturation conditions. The barrier ofV-type dislocation loops is higher than that of voids by more than one order of magnitude, with the former exceeding 35 eV at attainableV-supersaturation levels. Thus, voids can be nucleated, but not dislocation loops. This provides an explanation for the observations that, in Si crystals grown underV-supersaturation conditions, voids exist butV-type dislocation loops do not. Voids seriously degrade the Si device gate oxide integrity. It is highly probable that theD-type swirl defects in Si are nanoscopic voids. Our calculated results have also provided information for limiting the formation temperature range of theD-swirl defects to be lower than ∼1050 °C, and the SiVformation enthalpy to be above ∼3.0 eV. ©1997 American Institute of Physics.