Solid-phase crystallization (SPC) properties of Si1-xGex (0 less than or equal to x less than or equal to 0.3) layers on SiO2 have been investigated by using ellipsometric spectroscopy. Crystallinity of the SiGe layers abruptly increased in the middle of an annealing time and gradually saturated at values fairly below that of the single-crystal state. The incubation time of the nucleation significantly decreases with increasing x; the estimated incubation time in Si-0.7/Ge-0.3 is about 1/100 of that in Si. During the incubation time, it was observed that the crystallinity of SiGe layers continuously increased with increasing annealing time. This phenomenon represents the growth of some state precursory to nucleation which could not be observed by conventional methods. Since band structure is sensitive to the number of atoms in ordered positions, atomic rearrangements before the nucleation may be observed by present work. The crystallization time, defined as the time to complete SPC after nucleation, also showed a decrease with increasing x. The decrease in Si-Si bond energy caused by the introduction of Ge reduces the activation energy for lattice rearrangement and thus enhances the SPC of Si.