  Chemical vapor deposition (CVD) is a powerful method employed for high
quality monolayer crystal growth of 2D transition metal dichalcogenides with
much effort invested toward improving the growth process. Here, we report a
novel method for CVD based growth of monolayer molybdenum disulfide (MoS2) by
using thermally evaporated thin films of molybdenum trioxide (MoO3) as the
molybdenum (Mo) source for co-evaporation. Uniform evaporation rate of the MoO3
thin films provides uniform Mo vapor which promotes highly reproducible single
crystal growth of MoS2 throughout the substrate. These high-quality crystals
are as large as 95 um and were characterized by scanning electron microscopy,
Raman spectroscopy, photoluminescence spectroscopy, atomic force microscopy and
transmission electron microscopy. The bottom gated field effect transistors
fabricated using the as grown single crystals show n-type transistor behavior
with a good on/off ratio of 10^6 under ambient condition. Our results presented
here addresses the precursor vapor control during the CVD process and is a
major step forward toward reproducible growth of MoS2 for future semiconductor
device applications.
