Comparison study of the femtosecond laser-induced surface structures on silicon at an elevated temperature

The temperature dependency of femtosecond laser induced surface structures opens up a new scenario for studying ultrafast laser-mater interaction on the surface and a novel method for controlling the features of these structures. The shape and crystallinity of micro/nano surface structures created by femtosecond laser irradiation of n-type silicon (100) at elevated temperatures were compared in this study. Low spatial frequency laser induced periodic ripples structures (LSFL), micrometer-sized grooves, and spikes occur at room temperature as the number of pulses increases. At 400 °C, however, the grooves parallel to the polarization are the dominant structures, notwithstanding the presence of LSFL. As the temperature rises, the periodicities of LSFL increase, which we believe is due to a reduction in the oscillation of the surface plasmon polaritons due to the increased damping rate at higher temperatures. Furthermore, Raman spectra reveal that surface structures generated at 400 °C have higher crystallinity than those formed at 25 °C. Our simulations show that the better crystallinity at high temperatures is due to a slower resolidification velocity which is caused by a smaller temperature gradient and higher energy absorption. Our findings demonstrate that the features of femtosecond laser induced surface structures, such as periodicity and crystallinity, can be controlled by adjusting the substrate temperature simultaneously, paving the way for high crystallinity surface micro/nano-structures.