  Chemical vapor deposition (CVD) allows growing transition metal
dichalcogenides (TMDs) over large surface areas on inexpensive substrates. In
this work, we correlate the structural quality of CVD grown MoS$_2$ monolayers
(MLs) on SiO$_2$/Si wafers studied by high-resolution transmission electron
microscopy (HRTEM) with high optical quality revealed in optical emission and
absorption from cryogenic to ambient temperatures. We determine a defect
concentration of the order of 10$^{13}$ cm$^{-2}$ for our samples with HRTEM.
To have access to the intrinsic optical quality of the MLs, we remove the MLs
from the SiO$_2$ growth substrate and encapsulate them in hBN flakes with low
defect density, to reduce the detrimental impact of dielectric disorder. We
show optical transition linewidth of 5 meV at low temperature (T=4 K) for the
free excitons in emission and absorption. This is comparable to the best ML
samples obtained by mechanical exfoliation of bulk material. The CVD grown
MoS$_2$ ML photoluminescence is dominated by free excitons and not defects even
at low temperature. High optical quality of the samples is further confirmed by
the observation of excited exciton states of the Rydberg series. We optically
generate valley coherence and valley polarization in our CVD grown MoS$_2$
layers, showing the possibility for studying spin and valley physics in CVD
samples of large surface area.
