3D\nShape Reconstruction of Ge Nanowires during Vapor–Liquid–Solid\nGrowth under Modulating Electric Field

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