  Thin crystalline layers of TaAs Weyl semimetal (9 and 18 nm thick) are grown
by molecular beam epitaxy on GaAs(001) substrates. The (001) planes of the
tetragonal TaAs lattice are parallel to the GaAs(001) substrate, but the
corresponding in-plane crystallographic directions of the substrate and the
layer are rotated by 45{\deg}. In spite of a substantial lattice mismatch
(about 19%) between GaAs(001) substrate and TaAs epilayer no misfit
dislocations are observed at the GaAs(001)/TaAs(001) interface. Only stacking
fault defects in TaAs are detected with transmission electron microscopy.
Thorough X-ray diffraction measurements and analysis of the in-situ reflection
high energy electron diffraction images indicates that TaAs layers are fully
relaxed already at the initial deposition stage. Atomic force microscopy
imaging reveals the columnar structure of the layers, with lateral (parallel to
the layer surface) columns about 20 nm wide and 200 nm long. Both X-ray
diffraction and transmission electron microscopy measurements indicate that the
columns share the same orientation and crystalline structure.
