Promotion of a Mo-based ionic crystal precursor for MoS2 wafer growth†

Abstract

Two-dimensional MoS₂ semiconductors have emerged as a promising solution for extending Moore's law. Nevertheless, their wafer-scale growth from lab to fab is still in infancy stages within the semiconductor industry. The distribution, concentration, and reactivity of both sulfur and molybdenum precursors exert a substantial influence on the uniformity of MoS₂ wafers, including on parameters such as the grain size, thickness, and vacancy density. While considerable emphasis has been directed towards sulfur precursors—such as those derived from ZnS, which facilitate MoS₂ growth—the role of molybdenum precursors and their associated growth mechanisms remain inadequately understood. In this study, we investigated the effects of covalent and ionic molybdenum precursors, grounded in the principles of chemical vapor deposition, with the aim of identifying a universal synthesis pathway for wafer production. Our findings indicate that the reaction kinetics of Na₂MoO₄, a representative ionic precursor, are particularly advantageous for controlling wafer growth defects and enhancing surface homogeneity in comparison to those of MoO₃, a conventional covalent precursor. Evaporated [MoO₄]²⁻ ions, characterized by their smaller cluster size, exhibited high reactivity, facilitating uniform control over MoS₂ wafer characteristics. Furthermore, we demonstrate that a 2-inch monolayer MoS₂ film could be synthesized within a growth timeframe of 3–5 minutes using ionic precursors, achieving a mobility of 12 cm² V⁻¹ s⁻¹ and a maximum I_on/I_off ratio of 9.87 × 10⁹. This study elucidates the growth mechanisms of MoS₂ wafers and contributes to the advancement of MoS₂-based electronic systems.