  Quantum dot (QD) growth on high ($c_{3v}$) symmetry GaAs{111} surfaces holds
promise for efficient entangled photon sources. Unfortunately, homoepitaxy on
GaAs{111} surfaces suffers from surface roughness/defects and InAs deposition
does not natively support Stranski-Krastanov (SK) QD growth. Surfactants have
been identified as effective tools to alter the epitaxial growth process of
III-V materials, however, their use remains unexplored on GaAs{111}. Here, we
investigate Bi as a surfactant in III-As molecular beam epitaxy (MBE) on
GaAs(111)A substrates, demonstrating that Bi can eliminate surface
defects/hillocks in GaAs and (Al,Ga)As layers, yielding atomically-smooth
hillock-free surfaces with RMS roughness values as low as 0.13 nm. Increasing
Bi fluxes are found to result in smoother surfaces and Bi is observed to
increase adatom diffusion. The Bi surfactant is also shown to trigger a
morphological transition in InAs/GaAs(111)A films, directing the 2D InAs layer
to rearrange into 3D nanostructures, which are promising candidates for
high-symmetry quantum dots. The desorption activation energy ($U_{Des}$) of Bi
on GaAs(111)A was measured by reflection high energy electron diffraction
(RHEED), yielding $U_{Des}$ = 1.7 $\pm$ 0.4 eV. These results illustrate the
potential of Bi surfactants on GaAs(111)A and will help pave the way for
GaAs(111)A as a platform for technological applications including quantum
photonics.

Materials Science