Scalable Synthesis of Highly Crystalline MoSe₂ 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 I_on/I_off 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 I_on/I_off 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.