Anisotropic micro- and nanostructuring of amorphous silicon films by femtosecond laser pulses

In this paper it was shown that irradiation of amorphous hydrogenated silicon films by femtosecond laser pulses (1.25 μm) leads to formation of a one-dimensional surface relief with 1.20 ± 0.02 μm period. Orientation of the formed structures is determined by polarization vector of the radiation used and the total exposure dose. Nanocrystalline silicon phase with volume fraction from 40 to 67% is detected in the irradiated films, according to the analysis of Raman spectra. Observed micro- and nanostructuring processes are due to surface plasmon-polariton excitation and near-surface region nanocrystallisation, respectively, caused by high-power femtosecond laser pulses. Also, after the laser treatment with a large exposure dose, the formation of Si-III and Si-XII silicon polymorphous modifications was observed. The conductivity of the film increased by 3 orders of magnitude after femtosecond laser nanocrystallization compared to the untreated amorphous surface. The conductivity anisotropy of the irradiated regions was also observed due to the non-uniform intensity distribution in the laser beam cross-section and depolarizing effect of the surface structure.