Distinct fine and coarse ripples on 4H-SiC single crystal induced by femtosecond laser irradiation

Upon femtosecond pulsed-laser irradiation, periodic structures referred to as "ripples" were fabricated on the surface of a 4H-SiC single crystal. The periodic structures consisted of two concentric regions in the irradiated spots which were clearly distinguished by the period. Surface morphologies were characterized as a function of energy, accumulation number, and interval of pulses. The difference in the threshold of fine and coarse ripples was identified for the first time. The possible formation mechanisms of these structures were discussed.