Revealing Atomistic Mechanisms of Gold-Catalyzed Germanium Growth Using Molecular Dynamics Simulations

Abstract

The vapor−liquid−solid (VLS) method is considered a plausible technique for synthesizing germanium (Ge) nanostructures (e.g., nanowires), which have a broad range of applications due to their unique electronic properties and intrinsic compatibility with silicon. However, crystallization failures and material defects are still frequently observed in VLS processes, with insufficient understanding of their underlying mechanisms due to instrumental limitations for high-resolution in situ characterizations. Employing an accurate interatomic potential well fitted to the gold−germanium (Au−Ge) phase diagram, we performed molecular dynamics simulations for a systematic investigation of the Au-catalyzed growth process of Ge crystals. From the simulations, relationships were established between the overall Ge growth rate and several main synthesis conditions, including substrate crystallographic orientation, temperature, and Ge supersaturation in liquid. The dynamical behaviors of Ge atoms near the liquid−solid growing interface were captured, from which the atom surface stability and exchange rate were estimated for quantifying the atomistic details of the growth. These interface properties were further linked to the surface morphologies, to explain the observed orientation-dependent growing modes. This study sheds new light on the understanding of the VLS growth mechanisms of Ge crystals and provides scientific guidelines for designing innovative synthesis methods for similar nanomaterials.

Diffusion-Limited Crystal Growth of Gallium Nitride Using Active Machine Learning

“…Computationally, this is an unusually slow rate for epitaxial growth in nonreactive systems, e.g., the growth of semiconductors, such as Si, Ge, and their alloy SiGe, or metals, 29,39,40 which under ideal undercooling conditions can reach the maximum velocity at which it is possible to "pull" the crystal at growth rates up to 15−20 m/s. In comparison, the experimental growth velocity for GaN is exceptionally slow, 0.03−0.7 μm/min (equivalent to 5 × 10 −10 −1.17 × 10 −8 m/ s).…”