Material Synthesis and Device Aspects of Monolayer Tungsten Diselenide

Abstract

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.

Synthesis and Characterization of Metallic Janus MoSH Monolayer

“…Figure c shows the extracted carrier mobility of MoS 2 as a function of the applied gate voltage in different working regions . Evidently, the mobility of monolayer MoS 2 increases monotonically with increasing the gate voltage, as a result of the reduced Coulomb scattering due to the screening effect. − On the other hand, a peak mobility and the saturation region could be observed in the μ versus V g curves for multilayer TMDCs. , The measured mobility of the pristine MoS 2 monolayer was up to ∼14.2 cm 2 V –1 s –1 . The carrier concentration ( n 2D ) of MoS 2 and MoSH can be estimated by using the equation (see Discussion on Mobility, Mean Free Time and the Estimation of Carrier Concentration in SI): , Figure d displays the extracting carrier concentrations of MoS 2 and MoSH at different gate voltages.…”

A WSe2 vertical field emission transistor

“…Assuming an average 𝑉 𝑡ℎ ~16 𝑉 and using the output characteristics, we can evaluate the effective channel mobility 62 65 . The presence of traps, which can be filled or emptied during the forward (F) and reverse (R) gate sweep, manifests as a hysteresis in the transfer characteristics as we have reported and extensively studied for MoS2 back-gated transistors 59 .…”

“…Figs.2(c) and 2(d) show that threshold voltage, subthreshold swing, mobility and hysteresis width are affected by the applied drain bias. The dependence of the transistor parameters on 𝑉 𝑑𝑠 has been previously studied on similar WSe 2 devices and attributed to short channel effects65 . The 𝑉 𝑑𝑠 dependence, in the high bias regime, is further investigated in Figs.3(a) and 3(b), which show the transfer curves, the threshold voltage and the off…”

Hybrid/Integrated Silicon Photonics Based on 2D Materials in Optical Communication Nanosystems

“…and X stands for a chalcogen element (S, Se, Te). [65] The monolayer tungsten disulfide (WS 2 ), [66][67][68][69][70] tungsten diselenide (WSe 2 ), [71][72][73] molybdenum disulfide (MoS 2 ), [74][75][76] and molybdenum diselenide (MoSe 2 ) [77,78] are just four salient examples, whose direct bangap is in the range of 1.0-2.5 eV, [79] as presented in Figure 1b. Notably, the bandgaps of TMDCs can be engineered via numerous approaches, such as changing the layer numbers, inducing element defects, or forming van der Waals with other 2D materials, [80,81] allowing for a signficantly-large operation wavelngth regime.…”