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

Abstract

A Nd:YAG (λ = 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/cm2. The formation energy of surface ripples is significantly lower than the typical fluence of a few 100 mJ/cm2. 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/cm2, 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 × 20 mm2 shows uniform periodic surface textures, which can be employed in the display or photovoltaic applications.