Reduced Turn-On Voltage and Boosted Mobility in Monolayer WS₂ Transistors by Mild Ar⁺ Plasma Treatment

Abstract

Monolayer two-dimensional transition-metal dichalcogenides, such as tungsten disulfide (WS 2 ), are regarded as promising candidates for optoelectronic and electronic applications. Although theoretical calculations have predicted outstanding electronic properties of WS 2 , the performance of WS 2 -based electronic devices is still limited by the relatively high Schottky barrier and low carrier mobility. In this work, low-energy argon (Ar + ) plasma treatment was used as a nondestructive preconditioning technique to tailor the electrical properties of the WS 2 monolayer grown by chemical vapor deposition. Photoluminescence and Raman spectroscopy were used to monitor the modified optical properties of WS 2 with increasing plasma treatment time. An improved electrical conductivity was observed after a short-time plasma treatment. The physical mechanism was further revealed by a comparative study between topelectrode and bottom-electrode devices and simulation based on the density functional theory. It is concluded that mild Ar + plasma treatment can effectively lower the Schottky barrier height and the effective mass of carriers, which reduces the turn-on voltage and enhances the mobility, respectively. However, if the processing time is too long, the WS 2 lattice structure will be destroyed. This work has provided an effective method for manipulating the Schottky barrier and mobility of monolayer WS 2 transistors and paves the way for developing high-performance electronic devices based on 2D semiconductors. KEYWORDS: tungsten disulfide (WS 2 ), WS 2 field-effect transistors, Ar + plasma treatment, Schottky barrier (SB), work function

Unraveling the Mechanism of the 150-Fold Photocurrent Enhancement in Plasma-Treated 2D TMDs

“…13,14 The reduction of WS 2 monolayer-based fieldeffect transistors' (FETs) threshold voltage and mobility improvement were also seen after treatment with argon plasma due to the creation of sulfur vacancies in the WS 2 layer and removing surface contaminants from the sample. 15 Although some recent works on photocurrent in TMDs highlight the difference between measurements in different environments, 16,17 In the light of the aforementioned reports, we argue that the photocurrent enhancement of the TMD samples is a combined result of vacancy creation and oxide formation on the sample. In this work, we show on-chip tuning of the photocurrent response of WS 2 to significantly enhance the electrical signal while elongating the duration of the PPC under UV illumination.…”

“…WS 2 samples were also previously subjected to plasma-induced defect formation. There have been reports of photoluminescence enhancement and patching up sulfur vacancies of WS 2 by nitrogen plasma. , The reduction of WS 2 monolayer-based field-effect transistors’ (FETs) threshold voltage and mobility improvement were also seen after treatment with argon plasma due to the creation of sulfur vacancies in the WS 2 layer and removing surface contaminants from the sample . Although some recent works on photocurrent in TMDs highlight the difference between measurements in different environments, , none of the aforementioned plasma treatment experiments discussed the direct influence of plasma on photocurrent in relation to measurements performed in air and vacuum for WS 2 and MoS 2 .…”

Recent progress in plasma modification of 2D metal chalcogenides for electronic devices and optoelectronic devices

“…As mentioned above, p-type doping can be obtained through substitution doping, while introducing chalcogenide element defects for n-type doping has also been achieved with great properties, such as mobility, conductivity, doping concentration, on/off current ratio, threshold voltage, and subthreshold swing. 52,87,127,128,[153][154][155][156][157][158][159][160][161][162] For instance, hole mobilities of 8.4 cm 2 (V s) −1 and 137.7 cm 2 (V s) −1 have been achieved by Phosphorus (P) plasma-treated substitutional doping with the sheet hole concentrations of 2.4 × 10 12 cm −2 and 1.3 × 10 10 cm −2 in degenerately and non-degenerately doped p-type transistors, respectively (at V GS = 0 V), as shown in Fig. 9(a-d).…”

Plasma Processing and Treatment of 2D Transition Metal Dichalcogenides: Tuning Properties and Defect Engineering

“…As a result, bioreceptors can be immobilized on the surface more effectively, improving the sensitivity of BioFET devices. Recently, Hou et al 413 have employed a mild Ar plasma treatment to generate sulfur vacancies in WS 2 monolayers that reduce the effective mass of holes and the work function, while increasing the mobility. The results are reduced turn-on voltage in bottom-electrode FETs, and enhanced conductivity in both top-and bottom-electrode FETs.…”