Metallic Transport in Monolayer and Multilayer Molybdenum Disulfides by Molecular Surface Charge Transfer Doping

Abstract

Carrier modulation in transition-metal dichalcogenides (TMDCs) is of importance for applying electronic devices to tune their transport properties and controlling phases, including metallic to superconductivity. Although the surface charge transfer doping method has shown a strong modulation ability of the electronic structures in TMDCs and a degenerately doped state has been proposed, the details of the electronic states have not been elucidated, and this transport behavior should show a considerable thickness dependence in TMDCs. In this study, we characterize the metallic transport behavior in the monolayer and multilayer MoS2 under surface charge transfer doping with a strong electron dopant, benzyl viologen (BV) molecules. The metallic behavior transforms to an insulative state under a negative gate voltage. Consequently, metal–insulator transition (MIT) was observed in both monolayer and multilayer MoS2 correlating with the critical conductivity of order e 2/h. In the multilayer case, the BV molecules strongly modulated the topmost surface layer in the bulk MoS2; the transfer characteristics suggested a crossover from a heterogeneously doped state with a doped topmost layer to doping in the deep layers caused by the variation in the gate voltage. The findings of this work will be useful for understanding the device characteristics of thin-layered materials and for applying them to the controlling phases via carrier modulation.

Unusual selective monitoring of N,N-dimethylformamide in a two-dimensional layered field-effect transistor

“…The carrier concentration was 6.5 × 10 12 (cm − 2 ) based on the slope obtained by the linear approximation. These results indicate that the DMF molecules have medium strength in their electron donor ability to MoS2 compared with the previous molecular electron dopants of benzyl viologen, among others [36][37][38] .…”

Unusual Selective Monitoring of N,N-Dimethylformamide in a Two-Dimensional Material Field-Effect Transistor

“…The carrier concentration was 6.5 × 10 12 cm –2 based on the slope obtained by the linear approximation. These results indicate that the DMF molecules have medium strength in their electron donor ability to MoS 2 compared with the previous molecular electron dopants of benzyl viologen, among others. − The electron doping ability of the DMF molecule was observed in WS 2 and WSe 2 -MOSFETs as well (Figure S4).…”

Bright and Efficient Light‐Emitting Devices Based on 2D Transition Metal Dichalcogenides

“…Surface chargetransfer doping (SCTD) is one such technique, capable of doping TMDCs by interfacial charge transfer in a non-destructive manner. [243][244][245][246][247][248] When kept in close vicinity, a doping material (e.g., a metal oxide) dopes the host semiconductor p-type when its Fermi level (or electron-rich orbital in case of a molecular dopant) lies below that of the semiconductor, and vice versa. [248,249] This concept is illustrated schematically in Figure 7a.…”