Amorphous silicon (α-Si) film present an inexpensive and promising material for optoelectronic and nanophotonic applications. Its basic optical and optoelectronic properties are known to be improved via phase transition from amorphous to polycrystalline phase. Infrared femtosecond laser radiation can be considered as a promising nondestructive and facile way to drive uniform in-depth and lateral crystallization of α-Si films that are typically opaque in UV-visible spectral range. However, so far only a few studies reported on utilization of near-IR radiation for laser-induced crystallization of α-Si providing no information regarding optical properties of the resultant polycrystalline Si films. The present work demonstrates efficient and gentle single-pass crystallization of α-Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of laser-annealed films by atomic-force microscopy, optical, micro-Raman and energy-dispersive X-ray spectroscopy, as well as numerical modeling of optical spectra, confirmed efficient crystallization of α-Si and high-quality of the obtained films. Moreover, we highlight localized laser-driven crystallization of α-Si as a promising way for optical information encryption, anti-counterfeiting and fabrication of micro-optical elements.
Time-resolved study of laser emission in nitrogen gas pumped by two near IR femtosecond laser pulses