Periodic surface texturing of amorphous-Si thin film irradiated by UV nanosecond laser

Abstract

A Nd:YAG (lambda = 355 nm) nanosecond laser is used to anneal a 45-nm-thick amorphous-Si (a-Si) thin film on a glass substrate. Via scanning with a laser beam having a Gaussian shape at a repetition rate of 14 kHz, the surface of the a-Si film is crystallized, and laser-induced periodic surface structures (LIPSSs) are formed within the fluence range of 30-35 mJ/cm(2). The formation energy of surface ripples is significantly lower than the typical fluence of a few 1(X) mJ/cm(2) . Confocal Raman spectroscopy and atomic force microscopy reveal that the a-Si film is only crystallized near the top surface and that the surface ripples are aligned to the perpendicular direction of laser polarization, in accordance with the LIPSS model. For a laser fluence of >35 mJ/cm(2), the surface texture loses its periodicity but forms randomly distributed Si grains with a surface roughness of >40 nm. The laser processing on an a-Si film achieved by scanning up to 20 x 20 mm(2) shows uniform periodic surface textures, which can be employed in the display or photovoltaic applications. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement