Ablation and amorphization of crystalline Si by femtosecond and picosecond laser irradiation

The ablation and amorphization of crystalline Si by fermosecond and picosecond laser irradiations are reported in this paper. Laser pulse width was varied in the range of 100fs-200ps. We obtained the dependences of ablation rate and fluence for amorphization on laser pulse. width. At a lower fluence than a single-shot ablation threshold, femtosecond laser irradiation induced the amorphization of crystalline Si. We confirmed the thickness of an amorphous Si layer by transmission electron microscopy. The thickness of an amorphized layer, which was about 50 nm and almost uniform, did not depend on the number of irradiated laser pulses and fluence. The fluence range for amorphization decreased with increasing laser pulse width.