Self-assisted nucleation and vapor-solid growth of InAs nanowires on bare Si(111)

The nucleation and growth of InAs nanowires on bare Si(111) has been investigated by molecular beam epitaxy. Nontapered InAs nanowires with high aspect ratio were grown perpendicular to the substrate without the use of catalyst particles, surface oxide, or other substrate mask. The nucleation of InAs takes place in In-rich areas forming spontaneously on the substrate in the beginning of the growth process. As the nucleation proceeds, the local stoichiometry on the growth interface changes from In-rich to As-rich, and the growth continues in a vapor-solid mode. This transition to As-rich conditions is correlated with the evolution of nanowire morphology, that is, with the growth becoming strictly uniaxial and with well-defined vertical sidewalls forming. The diameter, the number density, and the axial growth rate of the nanowires were found to depend exclusively on the surface diffusivity of In adatoms on the substrate.