Salt-Assisted Chemical Vapor Deposition Synthesis of 2D WSe₂ and Its Integration in High Performance Field-Effect Transistors

Abstract

The synthesis of two-dimensional (2D) transitional metal dichalcogenides (TMDCs), including in the monolayer limit with control on crystallinity, is an important factor for their integration into a number of device platforms. Monolayer tungsten diselenide (WSe₂) has recently attracted a great deal of interest because of its tunable charge transport behavior, making it attractive for a variety of electronic and optoelectronic devices. However, the controlled and efficient synthesis of WSe₂ using chemical vapor deposition (CVD) is often challenging because of the high temperatures required to generate a steady flux of tungsten atoms in the vapor phase from the oxide precursors. Here, we use a salt (NaCl)-assisted process within the CVD furnace to reduce the growth temperature to ~750 °C, which is lower than the typical temperatures needed with conventional CVD for realizing monolayer WSe₂. The role of substrates also play an important role in the CVD growth process and we found that sapphire improves the optical and crystalline quality of both CVD-grown and mechanically exfoliated WSe₂ when compared with SiO₂/Si substrates. Finally, we fabricated WSe₂-based field-effect transistors using metal contacts of varying work functions and analyzed the interface properties in metal-2D WSe₂ junctions by extracting the interface state trap density, showing their promise for state-of-the-art electronic, optoelectronic, and quantum-optoelectronic devices using scalable synthesis routes.