Synthesis of wafer-scale monolayer MoS <sub>2</sub> on sapphire: Unlocking the influence of key growth parameters
Rong Song, Dingyi Shen, Dongyan Liu, Jingyi Liang, Zimei Zhang, Jingmei Tang, Liang Chen, Bo Li, Li Jia, Xidong Duan
Abstract
Large-scale synthesis of high-quality two-dimensional (2D) semiconductors, such as molybdenum disulfide (MoS<sub>2</sub>), is a prerequisite for their lab-to-fab transition. It is crucial to systematically explore and understand the influence of key synthetic conditions on the nucleation, uniformity, and quality of MoS<sub>2</sub> wafers. Here, we report the epitaxial growth of high-quality and uniform monolayer MoS<sub>2</sub> films on 2-in c-plane sapphire by chemical vapor deposition (CVD) method under optimized growth conditions (0–1 mg NaCl, adequate S/Mo ratio, and the addition of 0–1 sccm O<sub>2</sub>). We systematically explore the influence of critical synthetic conditions on the nucleation, and stitching of MoS<sub>2</sub> domains over the wafer scale, including the dosage of the alkali metal salt NaCl additive, the evaporation temperature of MoO<sub>3</sub>, the distance between MoO<sub>3</sub> and the substrate, and the flow rate of O<sub>2</sub>. Among them, the dosage of NaCl and the S/Mo ratio have important influences on the quality and film coverage of MoS<sub>2</sub>, while the flow rate of O<sub>2</sub> plays a key role in controlling the nucleation density and domain size. We further discovered that a-plane sapphire could easily guide the unidirectional growth of MoS<sub>2</sub> without the need for other specific synthetic conditions compared with c-plane and m-plane sapphire. The field-effect transistors (FETs) fabricated from the full-coverage films show an average and the highest mobilities of 28.5 and around 45 cm<sup>2</sup>·V<sup>−1</sup>·s<sup>−1</sup>, respectively.