The incorporation properties of implanted or deposited Sb into the Si lattice as a result of irradiation with a pulsed KrF ultraviolet laser have been compared. The surface melting dynamics resulting from laser irradiation have been studied in both cases by time‐resolved optical reflectivity. The distribution profiles of the Sb, deduced from Rutherford backscattering spectrometry and ion channeling measurements, show in both cases a maximum substitutional concentration of 2.1×1021cm−3. Substitutional solubility is limited by interface instabilities which develop during regrowth and lead to the formation of a well‐defined cellular structure, as shown by transmission electron microscopy. For the deposited case, we observe a much larger cellular microstructure in addition to the cells induced by interface instabilities. The large cell structure may result from convection‐induced instabilities.