Femtosecond-Laser-Induced Formation of Visible-Light-Emitting Structures Inside Silicon

We report a 680-nm photoluminescence (PL) from a femtosecond-laser-modified region inside silicon. Light-emitting structures were formed inside silicon by femtosecond laser irradiation in an air atmosphere. The formation of light-emitting structures arose from laser-induced oxygen doping, and the doping depths of a few hundred micrometers could be reached. PL intensities increased with increasing depth in the laser-modified region. The effects of the laser powers and scanning velocities were investigated. The peak positions of PL spectra showed almost no change after annealing. According to the Raman spectroscopy analysis, the defect states between the silicon nanocrystals and SiO₂ matrix contribute to the PL.