Transition
metal dichalcogenides (TMDCs), together with other two-dimensional
(2D) materials, have attracted great interest due to the unique optical
and electrical properties of atomically thin layers. In order to fulfill
their potential, developing large-area growth and understanding the
properties of TMDCs have become crucial. Here, we have used molecular
beam epitaxy (MBE) to grow atomically thin MoSe2 on GaAs(111)B.
No intermediate compounds were detected at the interface of as-grown
films. Careful optimization of the growth temperature can result in
the growth of highly aligned films with only two possible crystalline
orientations due to broken inversion symmetry. As-grown films can
be transferred onto insulating substrates, allowing their optical
and electrical properties to be probed. By using polymer electrolyte
gating, we have achieved ambipolar transport in MBE-grown MoSe2. The temperature-dependent transport characteristics can
be explained by the 2D variable-range hopping (2D-VRH) model, indicating
that the transport is strongly limited by the disorder in the film.