Metal-assisted etching of silicon in HF/H₂O₂ aqueous solutions has been used to fabricate luminescent silicon nanowires (SiNWs) and porous silicon. The impact of the gold catalyst layer thickness and the etching solution on the morphology of the synthesized nanostructures and the diameter of the obtained nanowires were systematically investigated. Scanning electron microscopy (SEM) analyses reveal that the morphology of the fabricated structures strongly depends on the composition of the solution and the thickness of the catalyst layer. It has been observed that SiNWs are formed in solutions with H₂O₂ ratios (ξ) below 10 %; increasing the H ₂O₂ concentration above this critical value leads to mesoporous (10 % < ξ < 14 %) and macroporous (14 % < ξ < 17 %) structures. Photoluminescence measurements show that SiNWs emit light at about 430 nm. Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) analyses were utilized to determine the origin of the emission in the silicon nanostructures. TEM imaging demonstrates that SiNWs are covered by a thin layer of porous silicon, which is assumed to be responsible for their light emission.

Silicon nanocrystals with dimensions of about 3 to 4 nm are fabricated by hydrogenation of amorphous silicon layers with thickness of about 15 nm. The strong binding of nanocrystals to the amorphous matrix, which prevents them from showing luminescence, is broken up by a plasma treatment process in the presence of H₂, N₂O, and SF₆. Regions with high nanocrystal density show more resistance against plasma etching. By controlling the etching parameters such as precursor flow rates during hydrogenation and plasma treatment processes, it seems possible to realize luminescent layers. Photoluminescence (PL) studies show that nanocrystals emit light around a wavelength of 550 nm. Multilayer structures have been fabricated to increase the PL intensity by separating luminescent nanocrystal layers with a 5 nm-thick layer of silicon oxynitride. The entire fabrication process has been performed in a conventional RF-PECVD reactor offering hope for realization of cost-effective silicon lightemitting structures. The low temperature nature of the proposed process could lead to the fabrication of light-emitting devices on low cost substrates like glass or even plastic.