The amorphous to crystal transition temperature has been measured in capped (Formula Formula) and uncapped Formula (GST) films (Formula thick) after irradiation with a Formula Formula in the range between Formula and Formula. In the capped samples the crystallization temperature increases with fluence (Formula at Formula). This effect is due to the doping of the GST layer with a few atom percent of recoiled O and Si atoms. The influence of the chemical species on the crystallization kinetics overcomes the effect of the ion-induced local rearrangement that instead decreases the transition temperature by a few degrees in the uncapped samples. Recoil implantation through the use of a thin capping layer may then be a viable alternative to the direct doping of chalcogenide thin films.