Detailed simulations of defect dynamics during Czochralski growth of silicon crystals demonstrate that the precipitation of either vacancies to form voids or self-interstitials to form stacking faults can be avoided by careful choice of crystal pull rate V and axial temperature gradient near the melt/crystal interface G(r). Almost perfect crystalline silicon is created, except for very small oxide precipitates, which are dissolved in subsequent annealing of the wafers. The presence of oxygen increases the range of V/G(r) for growth of this material.