We have investigated a Sb-enhanced solid phase epitaxy of Si on a p-type (100)Si substrate through intermixing of amorphous Si and Sb thin films and a subsequent recrystallization of the polycrystalline Si (poly-Si). By using cross-sectional transmission electron microscopy, we show that a high concentration of Sb enhances recrystallization of poly-Si, which eventually results in an epitaxial growth of Si. This is most likely due to an enhanced Si self-mobility caused by a Sb diffusion in the vicinity of the grain boundaries of the poly-Si. At the same time the doped layer was observed to serve as a diffusion source for doping the Si substrate. Secondary ion mass spectrometry measurements reveal the concentrations and the depth profiles of Sb in the Si substrate.