  MX monopnictide compounds (M=Nb,Ta, X = As,P) are prototypical
three-dimensional Weyl semimetals (WSMs) that have been shown in bulk single
crystal form to have potential for a wide variety of novel devices due to
topologically protected band structures and high mobilities. However, very
little is known about thin film synthesis, which is essential to enable device
applications. We synthesize TaAs(001) epilayers by molecular beam epitaxy on
GaAs(001) and provide an experimental phase diagram illustrating conditions for
single phase, single-crystal-like growth. We investigate the relationship
between nanoscale defects and electronic structure, using angle-resolved
photoemission spectroscopy, Kelvin probe microscopy and transmission electron
microscopy. Our results provide a roadmap and platform for developing 3D WSMs
for device applications.
