Formation of thicker silicon wires on a sufficiently cooled substrate during the gas phase zinc reduction reaction of SiCl4

Abstract

In this study, we demonstrate that thick silicon whiskers (wires) formed on a sufficiently cooled substrate. We used the gas phase zinc reduction reaction of SiCl4 at a gas reaction temperature of 910 °C. Wires formed via the tip-growth mode in the vapor–liquid–solid mechanism. When the substrate was the same temperature as the gas phase, the formation of multiple wires from a single point was observed. Conversely, this multiple formation was not observed, and thicker wires formed, on the sufficiently cooled substrate. We propose that splitting of a zinc catalytic droplet into several smaller ones is one of the main reasons for the formation of multiple wires. Suppression of this splitting on the cooled substrate was considered to be a main reason for the formation of thicker wires. We conducted a numerical approach to predict temperature profiles along a growing wire, because the growth rate of wires was about 5 mm min−1 and heating owing to the release of the latent heat for solidification was not negligible. Three processes, the conduction in a wire, the convection to the surrounding gas and the radiation via the surface of wire, were considered. We also considered the heating of the growing tip due to solidification as well. Our simulation revealed that the tip temperature of a rapidly growing wire increased and was higher than that of the substrate. The effect of substrate temperature and subsequent temperature profile for a growing wire was discussed.