Fabrication of Anisotropic Structures on the Surface of Amorphous Silicon by Femtosecond Laser Pulses

Anisotropic periodic relief in form of ripples was formed on surface of amorphous hydrogenated silicon (a-Si:H) films by femtosecond laser pulses with the wavelength of 1.25 μm. The orientation of the surface structures relative to laser radiation polarization vector depended on the number of laser pulses N acting on the film surface. When N = 30, the structures with 0.88 μm period were formed orthogonal to the laser radiation polarization; at N = 750 the surface structures had period of 1.12 μm and direction parallel to the polarization. The conductivity of the laser-modified a-Si:H films increased by 3 to 4 orders of magnitude, up to 3.8·10–5 (Ω∙cm)–1, due to formation of nanocrystalline Si phase with a volume fraction from 17 to 30%. Anisotropy of the dark conductivity, as well as anisotropy of the photoconductivity spectral dependences was observed in the modified films due to depolarizing influence of periodic microscale relief and uneven distribution of nanocrystalline Si phase within such laser-induced structure.

Oxidation of nanocrystalline silicon at room temperature and various humidity

Oxidation of HF vapor-etched nanocrystalline silicon films, prepared by drop coating from nanocrystalline Si sol in acetonitrile, was studied. Oxidation of nc-Si at room temperature in air with 5% and 86% relative humidity was observed by means of IR spectroscopy for 2 days. The change in film mass after 15 hours of oxidation was determined using quartz crystal microbalance. In dry air, film mass and integral intensity of bands attributed to vibrations in Si3-x‒Si‒Hx and Si-O-Si groups changed linearly with time. In humid air, intensity of in Si3-x‒Si‒Hx band decays exponentially and intensity of Si-O-Si band increases as a square root of oxidation time. Film mass gain after 15 hours of oxidation corresponds to an average oxide layer thickness of 0.02 nm in dry air and 0.51 nm in wet air.