During Si crystal growth, nucleation and growth of voids and vacancy-type dislocation loops under Si vacancy supersaturation conditions have been modeled. From nucleation barrier calculations, it is shown that voids can be nucleated, but not dislocation loops. The homogeneous nucleation rate of voids has been calculated for different temperatures by assuming different enthalpy of Si vacancy formation. The void growth process has been calculated using a moving boundary formulation. Matching the results of void nucleation and growth simulations and taking into account the competition between the two processes, limited time available, and the crystal cooling rate, it is shown that the experimentally observed void density and size data can be explained if the Si vacancy formation enthalpy is in the range of 2.8-3.4 eV and the void nucleation temperature is in the range of 970-1060 °C. © 1998 American Institute of Physics.