Bottom-up
growth offers precise control over the structure and
geometry of semiconductor nanowires (NWs), enabling a wide range of
possible shapes and seamless heterostructures for applications in
nanophotonics and electronics. The most common vapor–liquid–solid
(VLS) growth method features a complex interaction between the liquid
metal catalyst droplet and the anisotropic structure of the crystalline
NW, and the growth is mainly orchestrated by the triple-phase line
(TPL). Despite the intrinsic mismatch between the droplet and the
NW symmetries, its discussion has been largely avoided because of
its complexity, which has led to the situation when multiple observed
phenomena such as NW axial asymmetry or the oscillating truncation
at the TPL still lack detailed explanation. The introduction of an
electric field control of the droplet has opened even more questions,
which cannot be answered without properly addressing three-dimensional
(3D) structure and morphology of the NW and the droplet. This work
describes the details of electric-field-controlled VLS growth of germanium
(Ge) NWs using environmental transmission electron microscopy (ETEM).
We perform TEM tomography of the droplet–NW system during an
unperturbed growth, then track its evolution while modulating the
bias potential. Using 3D finite element method (FEM) modeling and
crystallographic considerations, we provide a detailed and consistent
mechanism for VLS growth, which naturally explains the observed asymmetries
and features of a growing NW based on its crystal structure. Our findings
provide a solid framework for the fabrication of complex 3D semiconductor
nanostructures with ultimate control over their morphology.