An alternative doping process to ion implantation for the production of very shallow p+-n junctions has been investigated. n-type silicon wafers covered with a boron-doped silicon oxide were submitted to thermal cycles with incoherent light radiation at temperatures between 900 and 1250 degrees C for times ranging from 20 to 120 s, in order to promote boron in-diffusion. The samples were characterised by sheet resistance measurements combined with sequential layer removal to obtain the carrier concentration-depth profiles. The results show the formation of a boron-rich surface layer above the normal boron solubility levels and a linear dependence of the sheet conductance on diffusion time, which suggests a chemical reaction at the silicon surface is the controlling factor for the boron in-diffusion. Moreover it was demonstrated that defect-free p+-n junctions with a junction depth as shallow as 50 nm are readily obtained.