Sub-millimeter size high mobility single crystal MoSe 2 monolayers synthesized by NaCl-assisted chemical vapor deposition.

Monolayer MoSe 2 is a transition metal dichalcogenide with a narrow bandgap, high optical absorbance and large spin-splitting energy, giving it great promise for applications in the field of optoelectronics. Producing monolayer MoSe 2 films in a reliable and scalable manner is still a challenging task as conventional chemical vapor deposition (CVD) or exfoliation based techniques are limited due to the small domains/nanosheet sizes obtained. Here, based on NaCl assisted CVD, we demonstrate the simple and stable synthesis of sub-millimeter size single-crystal MoSe 2 monolayers with mobilities ranging from 38 to 8 cm 2 V -1 s -1 . The average mobility is 12 cm 2 V -1 s -1 . We further determine that the optical responsivity of monolayer MoSe 2 is 42 mA W -1 , with an external quantum efficiency of 8.22%.