Femtosecond-laser surface structuring of amorphous and crystalline silicon

Abstract

The surface structuring of amorphous and crystalline silicon was performed by using ferntosecond-laser-induced phase transformations: i) amorphous-to-crystalline and ii) crystalline-to-amorphous. The amorphous silicon (a-Si) films were prepared on glass substrates by using plasma-enhanced chemical-vapor deposition. Two kinds of micropatterns were produced in the a-Si films: i) a two-dimensional (2D) pattern (a word 'q-Psi') was produced by using the inverse Fourier transform of a computer-generated hologram, and ii) laser-induced gratings (LIGs) were made by means of two-beam interference of near-infrared femtosecond-laser pulses. By using micro-Raman spectroscopy, optical microscopy, scanning electron microscopy, and transmission electron microscopy, the ferntosecond-laser pulses were found to induce a localized phase transformation from the amorphous to the crystalline phase, and the spatially-selected crystallization of a-Si was found to be responsible for the formation of patterns such as the LIG and the 2D pattern. Crystalline silicon (c-Si) with a SiO2 capping layer was also periodically modified by femtosecond holography. A micro-Raman study indicated that the LIG formation in c-Si could be ascribed to the spatially-selected amorphization of c-Si.