Low Temperature WS₂ Metal-Organic Chemical Vapor Deposition Using n-Bunc-W(CO)₅ for W Precursor

Abstract

Tungsten disulfide (WS2) is one of the representative two-dimensional layered materials, and its applications in various fields have been actively studied due to its preferable properties such as reasonably wide band gap (monolayer: 2.03 eV, bulk: 1.32 eV) [1] and excellent stability. In particular, large area, a few layer WS2 has a high potential as channel material for MOSFET in the next generation LSI. In most of the WS2 CVD reported so far, WF6 or W(CO)6 has been widely used for tungsten precursor as well as H2S for S precursor. However, there are critical problems for the precursors: WF6 is toxic, and W(CO)6 is solid and hard to supply to the reaction chamber. Sublimation supply of solids is not stable in terms of transport volume, and sometime clogging of pipes is also a concern. H2S is also highly toxic. In this study, a tungsten precursor of n-BuNC-W(CO)5 was investigated for WS2 deposition. One of its favorable characteristics is that it is liquid above 35 °C with stable vapor supply. It is also expected to interact with the substrate efficiently due to its polarity in the molecule. The vapor pressure is 1.2 torr at 115 °C, which is an appropriate for a CVD precursor. As a sulfur precursor, (t-C4H9)2S2 [2], which is non-toxic in contrast to H2S, was employed. WS2 thin films were grown by MOCVD in a cold-wall reactor, using the organic compounds introduced above as precursors for W and S, respectively, on silicon (001) or sapphire (0001) substrates. The deposited films were evaluated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (wavelength: 355 nm), and transmission electron microscopy (TEM). As a result, the continuous films were successfully obtained at the deposition temperature over 250 °C. XPS measurements showed the S/W ratio were slightly larger than the stoichiometric value of two (Fig. 1(a) and (b)). Residual C contamination was significantly reduced by elevating the deposition temperature over 300 °C. The Raman spectra confirmed the film was multi-layer WS2 with peak at 356 cm-1 (E1 2g) and 419 cm-1 (A1g) (Fig. 1(c)). TEM observation also revealed the film had a layered structures as is shown in the typical 2D materials (Fig. 1(d)). This study was partly supported by JST CREST Number JPMJCR16F4, Japan. Reference [1] J. Gusakova, X. Wang, L. L. Shiau, A. Krivosheeva, V. Shaposhnikov, V. Borisenko, V. Gusakov, and B. K. Tay, Phys Status Solidi. 214, 12 (2017). [2] C. Kirito, K. Yamazaki, Y. Hibino, Y. Hashimoto, H. Machida, M. Ishikawa, H. Sudoh, H. Wakabayashi, R. Yokogawa and A. Ogura, ECS Trans. 104, 3 (2021). Figure 1

Conformal deposition of WS2 layered film by low-temperature metal-organic chemical vapor deposition

“…This may be due to the different strains that the grown WS 2 thin film undergoes. [38][39][40] These results are consistent with our previous study 41) and those presented in other studies, [42][43][44] which verify that the films near the substrate surface have a 2H structure. This is consistent with the XPS results.…”

Phase-Engineered Tin Sulfides and Their Heterostructure with Ti3C2Tx MXene for All-Solid-State Flexible Asymmetric Supercapacitors

“…Likewise, the partition of C 1s spectra is linked to C–Ti, C–C, CO, and O–CO, which can be found at 283.9, 286.7, 288.2, and 292.6 eV, respectively. All of the deconvolution of the individual signal also well matched with the previous findings. − …”

“…These values are consistent with the previous literature. − Following relaxations, self-consistent field (SCF) calculations were conducted, and the density of states for α-SnS, β-SnS, and π-SnS structures are plotted in Figure S2e,f. The analysis revealed that β-SnS exhibited the lowest band gap of 0.52 eV among all considered SnS phases, aligning with previous theoretical studies . The minimal band gap or maximum conductivity in β-SnS may contribute to the superior electrochemical performance.…”

“…The predominant bonds are likely Sn–OH, resembling the common hydroxylated metal atoms found on oxide surfaces. Figure e demonstrates the splitting of S 2p spectra consisting of four peaks. − The peaks at 161.5 and 162.7 eV reveal the divalent nature of sulfur and belong to the S–Sn bond, which proves the formation of SnS. The peaks at 162.9 and 164.3 eV keep up a correspondence to the S–Ti–C bond.…”

“…Figure c exhibits the survey spectra of the heterostructure, indicating the presence of all of the constituent elements. In the heterostructure, the Sn 3d peak showed four peaks after deconvolution, from which peaks at 485.2 and 486.7 eV (corresponding to Sn 3d 5/2 ) demonstrate the presence of Sn 4+ , while the other two peaks at 493.6 and 495.1 eV (corresponding to Sn 3d 3/2 ) indicate Sn 2+ oxidation states (Figure d). ,− The significance of d-electrons in the chalcogens within metal dichalcogenides is more critical than it appears, capable of substantially modifying the physicochemical properties in a radical manner. The elevated level of Sn oxidation specifies the effective incorporation of oxygen-containing functional groups onto the Sn atom surface.…”