Solid-phase crystallization (SPC) properties of Si1-xGex (x = 0-0.3) layers on SiO2 have been investigated by using ellipsometric spectroscopy. Crystallinity of the Si(1-x)Gx(e) layers is significantly affected by both annealing-time and Ge-concentration x. The crystallinity abruptly increases at the end of the incubation time and gradually saturated during the crystallization time. As x increases, we have found that the nucleation is significantly enhanced and the estimated incubation time of x = 0.3 is about 1/100 of that of pure Si (x = 0). The crystallization time defined as the time to complete SPC after nucleation also significantly decreases with increasing x. Such changes of the crystallinity in the Ce-doped Si1-xGex layers perhaps originates from the difference between bond energies of Si-Si, Si-Ge, and Ge-Ge. The decrease of bond energy activates both nucleation and crystal-growth process in Si1-xGex layers.