Silicon Nanowires: Synthesis, optical properties and photonic applications

Group-IV semiconductor nanowires (NWs) are attracting the interest of a wide scientific community as building blocks for a wide range of future nanoscaled devices. We show that metal-assisted chemical etching of Si substrates is a powerful technique to obtain nanometer-size, high density and low-cost Si NWs with high and controllable aspect ratio. NWs obtained by this technique have exactly the same structure and doping of the substrate and present quantum confinement effects. Photoluminescence (PL) emission is very bright and tunable with NWs size according to quantum confinement. Light emitting devices based on Si NWs, showing an efficient electroluminescence emission at room temperature under low voltage excitation, have also been realized. The same synthesis approach has been also used for the realization of Si/Ge NWs, in order to obtain different confined structures of both Si and Ge inside each NW. PL emission properties of Si/Ge NWs are presented and discussed. Moreover we demonstrate that the design of new textures of NW materials and the optimization of size and spatial arrangement play a key role on the improvement of the optical properties, such as light trapping and multiple scattering phenomena. Furthermore, the possibility to manipulate a single Si NW by optical tweezers is demonstrated. The relevance of the reported results and their perspectives to open the route towards novel applications of Si nanostructures in photonics, are finally discussed.