Bi-containing III-V semiconductors constitute an exciting class of metastable
compounds with wide-ranging potential optoelectronic and electronic
applications. However, the growth of III-V-Bi alloys requires group-III-rich
growth conditions, which pose severe challenges for planar growth. In this
work, we exploit the naturally-Ga-rich environment present inside the metallic
droplet of a self-catalyzed GaAs nanowire to synthesize metastable
GaAs/GaAs$_{1-\text{x}}$Bi$_{\text{x}}$ axial nanowire heterostructures with
high Bi contents. The axial GaAs$_{1-\text{x}}$Bi$_{\text{x}}$ segments are
realized with molecular beam epitaxy by first enriching only the
vapor-liquid-solid (VLS) Ga droplets with Bi, followed by exposing the
resulting Ga-Bi droplets to As$_2$ at temperatures ranging from 270 to
380$\,^{\circ}$C to precipitate GaAs$_{1-\text{x}}$Bi$_{\text{x}}$ only under
the nanowire droplets. Microstructural and elemental characterization reveals
the presence of single crystal zincblende GaAs$_{1-\text{x}}$Bi$_{\text{x}}$
axial nanowire segments with Bi contents up to (10$\pm$2)$\%$. This work
illustrates how the unique local growth environment present during the VLS
nanowire growth can be exploited to synthesize heterostructures with metastable
compounds.