Silicon nanowires (NWs) can successfully be grown utilizing a vapor-liquid-solid (VLS) mechanism. In the case of a commonly used chemical vapour deposition (CVD) technique a Si-containing gas precursor is cracked at metal (Au) droplets acting as seeds. Si adatoms are subsequently dissolved in the liquid metal. Due to a supersaturation within this droplet, Si atoms precipitate predominantly at the liquid/solid interface, thus a nanowire of Si starts growing.
A different situation occurs, if NWs are grown by molecular beam epitaxy (MBE) via the VLS mechanism. For instance, the differences are in the role played by the metal seed, in the nanowires morphology, and in their aspect ratio. In particular, it concerns the surface diffusion of both the metal catalyst and Si, which strongly influences the growth process. The specific advantages of MBE are: i) epitaxial growth under ultra-high vacuum conditions, ii) clean surfaces, free of an oxide layer, iii) in-situ deposition of metal seeds, semiconductor materials, and dopants.
MBE growth of NWs can successfully be combined with a surface structuring, e.g. by electron-beam lithography and reactive plasma etching that is a way to get regular and periodic NW arrays.