Tunable Doping of Rhenium and Vanadium into Transition Metal Dichalcogenides for Two‐Dimensional Electronics

Abstract

Two‐dimensional (2D) transition metal dichalcogenides (TMDCs) with unique electrical properties are fascinating materials used for future electronics. However, the strong Fermi level pinning effect at the interface of TMDCs and metal electrodes always leads to high contact resistance, which seriously hinders their application in 2D electronics. One effective way to overcome this is to use metallic TMDCs or transferred metal electrodes as van der Waals (vdW) contacts. Alternatively, using highly conductive doped TMDCs will have a profound impact on the contact engineering of 2D electronics. Here, a novel chemical vapor deposition (CVD) using mixed molten salts is established for vapor–liquid–solid growth of high‐quality rhenium (Re) and vanadium (V) doped TMDC monolayers with high controllability and reproducibility. A tunable semiconductor to metal transition is observed in the Re‐ and V‐doped TMDCs. Electrical conductivity increases up to a factor of 108 in the degenerate V‐doped WS2 and WSe2. Using V‐doped WSe2 as vdW contact, the on‐state current and on/off ratio of WSe2‐based field‐effect transistors have been substantially improved (from ≈10–8 to 10–5 A; ≈104 to 108), compared to metal contacts. Future studies on lateral contacts and interconnects using doped TMDCs will pave the way for 2D integrated circuits and flexible electronics.

Controllable p‐Type Doping of 2D WSe2 via Vanadium Substitution

“…However, while various doping techniques can tune the electrical conductivity of TMDCs (e.g., surface charge transfer doping, [15] electrostatic doping, [16] intercalation, [17] and substitutional doping, [18,19] ) progress is still limited in truly scalable doping. Furthermore, even though "proof-of-concept" devices have been demonstrated based on doped TMDCs including vanadium dopants, [20][21][22][23][24] uniform distribution and precise control of the impurity density over a large scale and use of methods compatible with the state-of-the-art Si CMOS 300 mm process lines, still remains challenging. [19,25,26] Thus, scalable doping of TMDCs at a large temperature window with accurate control over the doping concentration is urgently needed.…”

Review of strategies toward the development of alloy two-dimensional (2D) transition metal dichalcogenides

“… Doping synthesis Method Ref. MoS 2 Mo Re 7 n-type 2.1 atomic % Molten salt CVD ( Li et al., 2021 ; Zhang et al., 2020a ) WS 2 W Fe 8 n-type 0.7–2.8 atomic % Liquid precursor-assisted technique ( Zhang et al., 2020a , 2020b ) NbS 2 Nb Cu 11 p-type 0–1.2 atomic % Powder metallurgy ( Liu et al., 2020 ) WS 2 , MoS 2 , WSe 2 , MoSe 2 Mo, W Rb 1 n-type ∼ 10 12 cm −2 In-situ surface doping ( Kang et al., 2017 ) WSe 2 , MoS 2 , WS 2 Mo, W V 5 p-type 2.7–5 atomic % CVD ( Li et al., 2021 ; Williamson et al., 2019 ) MoSe 2 , MoS 2 , MoSe 2 Mo, W W 6 p-type 2.083 atomic % – ( Williamson et al., 2019 ) NbS 2 , NbSe 2 Nb Li,Na 1 n-type 0.125 atomic % – ( Fan et al., 2017 ) MoS 2 , MoSe 2 , WS 2 , WSe 2 Mo, W Li,Na 1 n-type …”

Structure Engineering of 2D Materials toward Magnetism Modulation

“…[73] The appropriate choice of precursors is also of great importance for uniform doping. [83] 4.3. Defect Engineering…”