  Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted
great attention due to their physical and chemical properties that make them
promising in electronics and optoelectronics. Because of the difficulties in
controlling concentrations of solid precursors and spatially non-uniform growth
dynamics, it is challenging to grow wafer-scale 2D TMDCs with good uniformity
and reproducibility so far, which significantly hinders their practical use.
Here we report a vertical chemical vapor deposition (VCVD) design to grow
monolayer TMDCs with a uniform density and high quality over the whole wafer,
and with excellent reproducibility. The use of such VCVD design can easily
control the three key growth parameters of precursor concentration, gas flow
and temperature, which cannot be done in currently widely-used horizontal CVD
system. Statistical results show that VCVD-grown monolayer TMDCs including MoS2
and WS2 are of high uniformity and quality on substrates over centimeter size.
We also fabricated multiple van der Waals heterostructures by the one-step
transfer of VCVD-grown TMDC samples, owning to its good uniformity. This work
opens a way to grow 2D materials with high uniformity and reproducibility on
the wafer scale, which can be used for the scalable fabrication of 2D materials
and their heterostructures.

Applied Physics;Materials Science