Electrical and physical comparison of MoS₂ monolayers synthesized via CVD in different carrier gas environments

Transition metal dichalcogenides (TMDs) are an important family of two- dimensional (2D) materials currently being studied for implementation in next-generation electronics. Like graphene, this group of materials is a promising alternative to silicon as scaling effects begin to degrade silicon-based device performances. However, contrary to graphene, this family of 2D materials has an indirect bandgap in bulk form, and many members experience a shift to a direct bandgap in monolayers. MoS₂ is one of the most highly researched members of TMDs. With a direct bandgap of 1.8eV, the material is suited for applications from optoelectronics to spin electronics. One major difficulty in using MoS₂ in future devices is the struggle to produce large area, single crystalline layers. Chemical vapor deposition is one method of synthesizing single crystal MoS2. However, the large number of growth parameters makes optimization difficult. This study varies one parameter of growth, the carrier gas used in the synthesis of MoS₂, and compares the resulting electrical and surface characteristics of the synthesized MoS₂ layers. Hydrogen, nitrogen, and argon were the three carrier gases compared in this study. The samples grown using each carrier gas were also characterized with Raman spectroscopy and imaged with a scanning electron microscope to compare surface morphology and crystallinity. Back-gated field effect transistors were fabricated on each sample grown with each different carrier gas in order to compare electrical properties of the respective monolayers. Hydrogen is less commonly used as a carrier gas, but the resulting crystalline layers grown with H₂ displayed higher mobility and lower contact resistance than the layers grown with N₂ and Ar carrier gases. Other electrical properties compared included threshold voltage, channel resistance, and on/off ratio.