Material Synthesis and Device Aspects of Monolayer Tungsten Diselenide

In this paper, we investigate the synthesis of WSe₂ by chemical vapor deposition and study the current transport and device scaling of monolayer WSe₂. We found that the device characteristics of the back-gated WSe₂ transistors with thick oxides are very sensitive to the applied drain bias, especially for transistors in the sub-micrometer regime. The threshold voltage, subthreshold swing, and extracted field-effect mobility vary with the applied drain bias. The output characteristics in the long-channel transistors show ohmic-like behavior, while that in the short-channel transistors show Schottky-like behavior. Our investigation reveals that these phenomena are caused by the drain-induced barrier lowering (short-channel effect). For back-gated WSe₂ transistors with 280 nm oxide, the short-channel effect appears when the channel length is shorter than 0.4 µm. This extremely long electrostatic scaling length is due to the thick back-gate oxides. In addition, we also found that the hydrogen flow rate and the amount of WO₃ precursor play an important role in the morphology of the WSe₂. The hole mobility of the monolayer WSe₂ is limited by Columbic scattering below 250 K, while it is limited by phonon scattering above 250 K. These findings are very important for the synthesis of WSe₂ and accurate characterization of the electronic devices based on 2D materials.