Control of the size and position of silicon nanowires grown via the vapor-liquid-solid technique

The diameter and position of vapor-liquid-solid (VLS) grown Si nanowires can be controlled by exploiting the difference in Au condensation coefficient on Si and SiO 2 surfaces at elevated temperature. For low Au fluxes in the temperature range 520–700° C, Au condensation is completely selective to Si. Holes are etched through the surface oxide layer of a thermally oxidized Si(111) wafer to expose the Si. When Au is then evaporated onto the surface, the Au atoms condense selectively in the holes and form liquid Au/Si alloy balls. If the holes contain a small Si island protrusion formed by etching this acts as an alloy nucleation center and the alloy can agglomerate to form a single ball, the diameter of which is determined by the diameter of the hole and the total dose of Au. When silane gas is then introduced into the chamber as the Si source gas in the VLS reaction each alloy ball grows to form a Si wire of controlled diameter and position.