Material and lattice defect properties of silicon and germanium relevant for device processing are discussed and compared with respect to their impact on crystal pulling, device processing, and diode leakage current. It is shown that both semiconductors are very similar when comparing their material properties at the same temperature T normalized to the melt temperature T-m. In other respects, however, like the diffusion of dopants, Ge behaves quite differently. With respect to diode leakage, germanium is more sensitive to metal contamination than silicon at the same device operation temperature. (C) 2007 The Electrochemical Society.