| Summary: | Amorphous silicon (<inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>-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 to be a promising nondestructive and facile way to drive uniform in-depth and lateral crystallization of <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>-Si films that are typically opaque in UV-visible spectral range. However, so far only a few studies reported on use of near-IR radiation for laser-induced crystallization of <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>-Si providing less information regarding optical properties of the resultant polycrystalline Si films demonstrating rather high surface roughness. The present work demonstrates efficient and gentle single-pass crystallization of <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>-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 <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>-Si and high-quality of the obtained films. Moreover, we highlight localized laser-induced crystallization of <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>-Si as a promising way for optical information encryption, anti-counterfeiting and fabrication of micro-optical elements.
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