Infrared‐absorption measurements on carbon‐implanted silicon are reported. A localized vibrational mode for substitutional carbon has been observed in annealed samples and in samples implanted at 500°C. The results suggest that between 40 and 60% of the implanted ions occupy substitutional sites. A broad absorption band which shifts to shorter wavelength on annealing has been observed and is attributed to the formation of SiC microcrystals. Absorption bands at 1097, 750, 640, and 625 cm−1have been observed in pulled crystals. It is suggested that these bands arise due to the presence of carbon‐oxygen complexes formed during implantation.