Spatial delocalization of absorption and emission process in silicon nanowires

Abstract

Dependence of optical properties of porous silicon nanowires on their size has been investigated here. Based on the experimental evidence, a new model to explain the process of absorption and photoluminescence in these Si nanowire samples has been proposed. Three different samples, with different nanowire diameters, have been prepared using metal-induced etching of silicon wafers. These wafers have different doping type and doping concentration which results in silicon nanowires of different diameters embedded with Si nanostructures of sizes around the Bohr's exciton radius. The absorption properties of these different types of Si nanostructures show a strong size dependence. However, the photoluminescence spectrum does not show any direct dependence on the size of the nanostructures, doping levels and type of silicon wafer used for fabrication of silicon nanostructures. It is also observed that the photoluminescence life time from these structures inversely depends on the size of the nanostructures whereas directly depends on the porosity, thus defects, in the samples. Based on these results it has been shown that the absorption of photons in these porous silicon nanowires happens in the silicon nanostructures embedded in the nanowires while the photoluminescence emission originates due to the surrounding porous SiOx.