Effects of dopant additions on interface stability in zone‐melting recrystallization (ZMR) of silicon thin films have been investigated through computer simulation and experiments. The computer simulation has shown that a critical scanning speedV* exists such that the critical wavelength &lgr;* of the solidifying interface increases with scanning speed belowV* due to radiative supercooling, while &lgr;* decreases with scanning speed aboveV* due to constitutional supercooling. Experiments determined thatV* decreased with additions of B and P, which was expected from the results of the computer simulation. The primary defect spacings after ZMR was found to increase with the addition of dopants prior to ZMR. ©1995 American Institute of Physics.