ИСТИНА

Femtosecond laser pulses with high emission intensity and low photon energy can be used to achieve uniform nanostructuring and modification over the entire volume of siliceous films [1]. This nanostructuring method also leads to anisotropy of structural, electrical and optical properties of processed films. For example, surface periodic structures can be produced [2]. Femtosecond laser radiation also can be used to enhance light absorption and reduce Staebler-Wronski effect in amorphous hydrogenated silicon films (a-Si:H) for potential applications in photovoltaics. In this paper, a-Si:H films irradiated by femtosecond laser pulses (1250 nm, 100 fs) were investigated. A surface profile with period equal to the laser spot diameter (150 mkm) was formed by means of laser beam movement in the raster mode. Scanning electron microscopy also revealed presence of one-dimensional periodic structure, perpendicular to polarization of the incident beam on the treated surface, with 0.36±0.03 or 1.11±0.05 μm period. This result is in agreement with the data of [3]. Electrical measurements have shown that the conductivity of a-Si:H film after irradiation with femtosecond laser pulses increased up to 3 orders of magnitude due to dehydrogenation and nanocrystallization of the film [4]. The conductivity along the raster lines and periodic structures is almost threefold greater than in the perpendicular direction. A possible explanation of this effect may be given by non-uniform crystallization of amorphous silicon, and the electric field anisotropic depolarization inside the surface periodic structure. This work was financially supported by the Russian Foundation for Basic Research (project 16-32-80066). [1] A. V. Emelyanov, M. V. Khenkin, A. G. Kazanskii, et al., Femtosecond laser induced crystallization of hydrogenated amorphous silicon for photovoltaic applications, Thin Solid Films, 556, pp. 410–413, (2014). [2] G.A. Martsinovsky, G.D. Shandybina, Yu.S. Dementeva et al., Surface electromagnetic wave excitation in semiconductors at femtosecond laser action, Semiconductors, 43, pp. 1339–1345, (2009). [3] R. Drevinskas, M. Beresna, M. Gecevičius et al., Giant birefringence and dichroism induced by ultrafast laser pulses in hydrogenated amorphous silicon, Appl. Phys. Letters, 106, art. 171106 (2015). [4] A.V. Emelyanov, A.G. Kazanskii, P.K. Kashkarov et al., Effect of the femtosecond laser treatment of hydrogenated amorphous silicon films on their structural, optical, and photoelectric properties, Semiconductors, 46, pp. 769–774, (2012).