Realization of Vertical and Zigzag Single Crystalline Silicon Nanowire Architectures

Silicon nanowire (SiNW) ensembles with vertical and zigzag architectures have been realized using wet chemical etching of bulk silicon wafers (p-Si(111) and p-Si(100)) with a mask of silver nanoparticles that are deposited by wet electroless deposition. The etching of SiNWs is based on subsequent treatments in chemical solutions such as 0.02 M aqueous solutions of silver nitrate (AgNO 3 ) followed by 5 M hydrofluoric acid and 30% hydrogen peroxide (H 2 O 2 ). The etching of the Si wafers is mediated by the reduction of silver on the silicon surface and in parallel by the oxidation of Si thereby forming SiO 2 which is dissolved in the HF surroundings. The morphology of the starting silver (Ag) layer/Ag nanoparticles that form during processing on the Si wafer surfaces strongly influences the morphology of the SiNW ensembles and homogeneity of the etch profile. Our observations suggest that the Ag layer/Ag nanoparticles not only catalyze the wet chemical etching of silicon but also strongly catalyze the decomposition of H 2 O 2 so that the temperature of the etching solution substantially increases (strong exothermic reaction) and thus the etching velocity of bulk material. The morphology and microstructure of single crystalline SiNWs with respect to their crystallographic orientation was investigated by scanning (SEM) and transmission electron (TEM) microscopies and by electron backscatter diffraction (EBSD) in an SEM. Straight SiNWs as well as zigzag SiNWs can be realized depending on processing peculiarities. The optical characteristics such as absorption, transmission, and reflectance of the different silicon 1D architectures were investigated in an integrating sphere. Strong absorption and less reflection of visible and near-infrared light by the SiNW ensembles suggest that such material can be applied in the fields of opto-electronics, photonics and photovoltaics.