Optical, structural and morphological studies of nanostructures fabricated on silicon surface by femtosecond laser irradiation

We report here a detailed analysis of the ultrashort laser pulse irradiation effects on a single crystalline silicon surface. A systematic study has been performed to understand the surface morphological changes under irradiation with ultrashort laser pulses by changing different input laser parameters such as laser fluence, laser pulse number, and incident laser polarization. Field emission scanning electron microscopy images reveal the formation of laser induced periodic sub-wavelength surface structures directly on bulk surface. The orientation of the formed sub-wavelength surface structures is perpendicular to the incident laser polarization and their morphology and spatial periodicity strongly depend on the applied laser fluence and laser pulse number. The sub-wavelength surface structures are accompanied by the formation of a large density of silicon nanoparticles which possess broad visible photoluminescence ranging from 410 to 680 nm which is due to superficial oxidation of silicon during laser irradiation. The amount of oxygen incorporated into silicon strongly depends on laser parameters such as laser fluence and number of laser pulses.