Layer-Controlled, Wafer-Scale, and Conformal Synthesis of Tungsten Disulfide Nanosheets Using Atomic Layer Deposition

Abstract

The synthesis of atomically thin transition-metal disulfides (MS2) with layer controllability and large-area uniformity is an essential requirement for their application in electronic and optical devices. In this work, we describe a process for the synthesis of WS2 nanosheets through the sulfurization of an atomic layer deposition (ALD) WO3 film with systematic layer controllability and wafer-level uniformity. The X-ray photoemission spectroscopy, Raman, and photoluminescence measurements exhibit that the ALD-based WS2 nanosheets have good stoichiometry, clear Raman shift, and bandgap dependence as a function of the number of layers. The electron mobility of the monolayer WS2 measured using a field-effect transistor (FET) with a high-k dielectric gate insulator is shown to be better than that of CVD-grown WS2, and the subthreshold swing is comparable to that of an exfoliated MoS2 FET device. Moreover, by utilizing the high conformality of the ALD process, we have developed a process for the fabrication of WS2 nanotubes.

Synthesis, properties and potential applications of two-dimensional transition metal dichalcogenides

“…Raman (lower left) and PL spectra (lower right) for the obtained MoS 2 trilayer after MoO 3 sulfurization [63]. (d) Synthesis procedure for the ALD-based WS 2 nanosheets [65]. (e) OM images of the transferred WS 2 nanosheet on the SiO 2 substrate for the single-, bi-, and tetralayered thicknesses [65].…”

“…(d) Synthesis procedure for the ALD-based WS 2 nanosheets [65]. (e) OM images of the transferred WS 2 nanosheet on the SiO 2 substrate for the single-, bi-, and tetralayered thicknesses [65]. (f) AFM images and height profiles (inset) of the WS 2 nanosheet transferred onto the SiO 2 substrate for the single-, bi-, and tetralayered thicknesses [65].…”

“…(e) OM images of the transferred WS 2 nanosheet on the SiO 2 substrate for the single-, bi-, and tetralayered thicknesses [65]. (f) AFM images and height profiles (inset) of the WS 2 nanosheet transferred onto the SiO 2 substrate for the single-, bi-, and tetralayered thicknesses [65]. (g) Raman spectra for the single-(red), bi-(blue), and tetralayer (black) WS 2 nanosheets on SiO 2 substrates [65].…”

Top‐Down Integration of Molybdenum Disulfide Transistors with Wafer‐Scale Uniformity and Layer Controllability

“…[17] So far, synthesis for high quality MoS 2 films by sulfurizing MoO 3 deposited by ALD have rarely been reported. [18][19][20] In the published work, for example, large area amorphous MoS 2 thin films have been grown by ALD with molybdenum hexacarbonyl (Mo(CO) 6 ) and dimethyldisulfide (DMDS (CH 3 S 2 CH 3 )) as the precursors of Mo and S, [6,7] respectively. However, DMDS is highly toxic and the electrical properties of the as deposited MoS 2 films were not studied.…”

Progress on Crystal Growth of Two-Dimensional Semiconductors for Optoelectronic Applications

“…Spatially inhomogeneous mixtures of monolayer, multi-layer, and non-deposition region on the wafer could be avoided. Nevertheless, as mentioned above, the crystallinity of the ALD-involved films and the device performance still need to be improved [70]. Although wafer-scale uniformity could be achieved in various synthesis methods as discussed above, the growth of high-quality large-area single crystal thin film is still the main challenge for further nanoelectronic applications of TMDCs.…”