  Despite its potential in the fields of optoelectronics and topological
insulators, experimental electronic band structure studies of Bi-doped GaAs are
scarce. The reason is the complexity of growth which tends to leave bulk and in
particular surface properties in an undefined state. Here we present an in
depth investigation of structural and electronic properties of GaAsBi epilayers
grown by molecular beam epitaxy with high (001) crystalline order and
well-defined surface structures evident from low-energy electron diffraction.
X-ray and ultraviolet photoemission spectrocopy as well as angle-resolved
photoemission data at variable photon energies allows to disentangle a Bi-rich
surface layer with $(1\times3)$ symmetry from the effects of Bi atoms
incorporated in the GaAs bulk matrix. The influence of Bi concentrations up to
$\approx 1$\% integrated in the GaAs bulk are visible in angle-resolved
photoemission spectra after mild ion bombardment and subsequent annealing
steps. Interpretation of our results is obtained via density functional theory
simulations of bulk and $\beta 2(2\times 4)$ reconstructed slab geometries with
and without Bi. Bi-induced energy shifts in the dispersion of GaAs heavy and
light hole bulk bands are evident both in experiment and theory, which are
relevant for modulations in the optical band gap and thus optoelectronic
applications.
