  The growth of Sn-rich group-IV semiconductors at the nanoscale provides new
paths for understanding the fundamental properties of metastable GeSn alloys.
Here, we demonstrate the effect of the growth conditions on the morphology and
composition of Ge/GeSn core/shell nanowires by correlating the experimental
observations with a theoretical interpretation based on a multi-scale approach.
We show that the cross-sectional morphology of Ge/GeSn core/shell nanowires
changes from hexagonal to dodecagonal upon increasing the supply of the Sn
precursor. This transformation strongly influences the Sn distribution as a
higher Sn content is measured under the {112} growth front. Ab-initio DFT
calculations provide an atomic-scale explanation by showing that Sn
incorporation is favored at the {112} surfaces, where the Ge bonds are
tensile-strained. A phase-field continuum model was developed to reproduce the
morphological transformation and the Sn distribution within the wire, shedding
light on the complex growth mechanism and unveiling the relation between
segregation and faceting. The tunability of the photoluminescence emission with
the change in composition and morphology of the GeSn shell highlights the
potential of the core/shell nanowire system for opto-electronic devices
operating at mid-infrared wavelengths.
