Scalable Synthesis of Highly Crystalline MoSe 2 and Its Ambipolar Behavior.

Atomically thin, two-dimensional material molybdenum diselenide (MoSe2 ) has been shown to exhibit significant potential for diverse applications. The intrinsic band gap of MoSe2 allows it to overcome the shortcomings of the zero-band-gap graphene, while its higher electron mobilities when compared to molybdenum disulfide (MoS2 ) make it more appropriate for practical devices in electronics and optoelectronics. However, its controlled growth has been an ongoing challenge for investigations and practical applications of the material. Here, we present an atmospheric pressure chemical vapor deposition (CVD) method to achieve highly crystalline, single- and few-layered MoSe2 using a SiO2 /Si substrate. Our findings suggested that careful optimization of the flow rate can result in the controlled growth of large-area MoSe2 with desired layer numbers due to the adjustment of gaseous MoSe2 partial pressure and nucleation density. The FETs fabricated on such as-synthesized MoSe2 displayed different transport behaviors depending on the layer numbers, which can be attributed to the formation of Se vacancies generated during low flow rates. Monolayer MoSe2 showed n-type characteristics with an Ion /Ioff ratio of ∼106 and a carrier mobility of ∼19 cm2 V-1 s-1 , whereas bilayer MoSe2 showed n-type-dominant ambipolar behavior with an Ion /Ioff ratio of ∼105 and a higher mobility of ∼65 cm2 V-1 s-1 for electrons as well as ∼9 cm2 V-1 s-1 for holes. Our results provide a foundation for property-controlled synthesis of MoSe2 and offer insight on the potential applications of our synthesized MoSe2 in electronics and optoelectronics.