Synthesis of wafer-scale monolayer MoS2 on sapphire: Unlocking the influence of key growth parameters

Abstract

Large-scale synthesis of high-quality two-dimensional (2D) semiconductors, such as molybdenum disulfide (MoS2), 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 MoS2 wafers. Here, we report the epitaxial growth of high-quality and uniform monolayer MoS2 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 O2). We systematically explore the influence of critical synthetic conditions on the nucleation, and stitching of MoS2 domains over the wafer scale, including the dosage of the alkali metal salt NaCl additive, the evaporation temperature of MoO3, the distance between MoO3 and the substrate, and the flow rate of O2. Among them, the dosage of NaCl and the S/Mo ratio have important influences on the quality and film coverage of MoS2, while the flow rate of O2 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 MoS2 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 cm2·V−1·s−1, respectively.