Barrier-assisted vapor phase CVD of large-area MoS(2) monolayers with high spatial homogeneity

Atomically thin molybdenum disulphide (MoS(2)) is a direct band gap semiconductor with negatively charged trions and stable excitons in striking contrast to the wonder material graphene. While large-area growth of MoS(2) can be readily achieved by gas-phase chemical vapor deposition (CVD), growth of continuous MoS(2) atomic layers with good homogeneity is indeed one of the major challenges in vapor-phase CVD involving all-solid precursors. In this study, we demonstrate the growth of large-area continuous single crystal MoS(2) monolayers on c-plane sapphire by carefully positioning the substrate using a facile staircase-like barrier. The barrier offered great control in mitigating the secondary and intermediate phases as well as second layer nucleation, and eventually a continuous monolayer with high surface homogeneity is realized. Both micro-Raman and high-resolution transmission electron microscopy (HRTEM) results confirmed the high structural quality of the grown MoS(2) layers. Using low temperature photoluminescence spectroscopy, additional pieces of information are provided for the strong band-edge emission in the light of vacancy compensation and formation of Mo–O bonding. The monolayer MoS(2) transferred to SiO(2)/Si exhibited a room temperature field-effect mobility of ∼1.2 cm(2) V(−1) s(−1) in a back-gated two-terminal configuration.