  Scalable fabrication of high quality photodetectors derived from
synthetically grown monolayer transition metal dichalcogenides is highly
desired and important for wide range of nanophotonics applications. We present
here scalable fabrication of monolayer MoS2 photodetectors on sapphire
substrates through an efficient process, which includes growing large scale
monolayer MoS2 via chemical vapor deposition (CVD), and multi-step optical
lithography for device patterning and high quality metal electrodes
fabrication. In every measured device, we observed the following universal
features: (i) negligible dark current $(I_{dark}\leqslant10 fA)$; (ii) sharp
peaks in photocurrent at $\sim$1.9eV and $\sim$2.1eV attributable to the
optical transitions due to band edge excitons; (iii) a rapid onset of
photocurrent above $\sim$2.5eV peaked at $\sim$2.9eV due to an excitonic
absorption originating from the van Hove singularity of MoS$_2$. We observe low
($\leqslant 300\%$) device-to-device variation of photoresponsivity.
Furthermore, we observe very fast rise time $\sim$0.5 ms, which is three orders
of magnitude faster than other reported CVD grown 1L-MoS$_2$ based
photodetectors. The combination of scalable device fabrication, ultra-high
sensitivity and high speed offer a great potential for applications in
photonics.
