Growth of germanium nanowires on silicon(111) substrates by molecular beam epitaxy.

Heteroepitaxial growth of Ge nanowires was carried out on Si(111) substrates by MBE. Au seeds were used as precursor for the VLS growth of the nanowires. Even if the Au droplets do not act as catalyst for the dissociation of gas, they are local preferential areas where the energetic barrier of Ge nucleation is lowered compare to the remaining non activated surface. Two sets of Au seeds were used as precursors for the VLS process. The first set have an average diameter of 125 nm and the second of 25 nm. In-situ RHEED monitoring showed a Au wetting layer between these seeds before the nanowires growth as well as at the end of the Ge nanowires growth. It means that the wetting layer acted as a surfactant from the Si(111) surface to the Ge grown layer between the nanowires. Analysis of SEM images brought the fact that the diffusion of gold from the droplets on the surface and the sidewalls of the nanowires via the Ostwald ripening is a key parameter of the growth of the nanowires.