By annealing Si layers amorphised by ion-implantation with a cw CO2 laser beam in oxygen rich environments, it has been possible to incorporate O atoms into the recrystallized lattice. Absorption measurements on such regrown layers by infrared spectrometry have shown that the impurities are preferentially bonded into substitutional lattice sites, rather than existing interstitially. Supplementary RHEED studies have indicated that ß-cristobalite, a crystalline form of SiO2, has been formed. These investigations highlight the importance of the ambient during cw laser annealing. © 1983 Springer-Verlag.