Atomistic mechanisms of orientation and temperature dependence in gold-catalyzed silicon growth

Abstract

Gold-catalyzed vapor-liquid-solid (VLS) growth is widely used in the synthesis of silicon-based low-dimensional nano-structures. However, its growth mechanisms are not fully understood yet. In this paper, we systematically study the orientation and temperature dependences in the VLS process, by means of long molecular dynamics (MD) simulations up to 100 ns using an MEAM potential that well reproduces the binary phase diagram. The crystal growth velocities are extracted from the simulations under various conditions for {110} and {111} orientations, respectively. Our data suggest a linear dependence of the growth velocity on the Si supersaturation for {110} growth, in contrast to a non-linear dependence for {111} growth. By analyzing the surface morphologies, this difference is linked to the continuous growth mechanism on the {110} substrate and the island nucleation controlled growth on the {111} substrate. Furthermore, we find that the {111} growth in our MD simulations operates in the regime where the nucleation rate is higher than the island expansion rate. This is traced to the formation of a gold saturated monolayer above the nucleated Si island, impeding its further growth. Also, it is found that the atom activity near the {111} interface is lower, explaining the smaller growth velocity of the {111} surface than that of the {110} surface.