  Two-dimensional materials (2D) arranged in hybrid van der Waals (vdW)
heterostructures provide a route toward the assembly of 2D and conventional
III-V semiconductors. Here, we report the structural and electronic properties
of single layer WSe2 grown by molecular beam epitaxy on Se-terminated
GaAs(111)B. Reflection high-energy electron diffraction images exhibit sharp
streaky features indicative of a high-quality WSe2 layer produced via vdW
epitaxy. This is confirmed by in-plane x-ray diffraction. The single layer of
WSe2 and the absence of interdiffusion at the interface are confirmed by high
resolution X-ray photoemission spectroscopy and high-resolution transmission
microscopy. Angle-resolved photoemission investigation revealed a well-defined
WSe2 band dispersion and a high p-doping coming from the charge transfer
between the WSe2 monolayer and the Se-terminated GaAs substrate. By comparing
our results with local and hybrid functionals theoretical calculation, we find
that the top of the valence band of the experimental heterostructure is close
to the calculations for free standing single layer WSe2. Our experiments
demonstrate that the proximity of the Se-terminated GaAs substrate can
significantly tune the electronic properties of WSe2. The valence band maximum
(VBM, located at the K point of the Brillouin zone) presents an upshifts of
about 0.56 eV toward the Fermi level with respect to the VBM of WSe2 on
graphene layer, which is indicative of high p-type doping and a key feature for
applications in nanoelectronics and optoelectronics.
