Scalable Synthesis of Highly Crystalline MoSe and Its Ambipolar Behavior.

Atomically thin, two-dimensional material molybdenum diselenide (MoSe) has been shown to exhibit significant potential for diverse applications. The intrinsic band gap of MoSe allows it to overcome the shortcomings of the zero-band-gap graphene, while its higher electron mobilities when compared to molybdenum disulfide (MoS) 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 MoSe using a SiO/Si substrate. Our findings suggested that careful optimization of the flow rate can result in the controlled growth of large-area MoSe with desired layer numbers due to the adjustment of gaseous MoSe partial pressure and nucleation density. The FETs fabricated on such as-synthesized MoSe 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 MoSe showed n-type characteristics with an I/I ratio of ∼10 and a carrier mobility of ∼19 cm V s, whereas bilayer MoSe showed n-type-dominant ambipolar behavior with an I/I ratio of ∼10 and a higher mobility of ∼65 cm V s for electrons as well as ∼9 cm V s for holes. Our results provide a foundation for property-controlled synthesis of MoSe and offer insight on the potential applications of our synthesized MoSe in electronics and optoelectronics.