Synthesis of Nb-Doped-WS₂–NbS₂: A Degenerate-Semiconductor–Metal Heterostructure

The synthesis of semiconductor–metal (S–M) heterostructures comprising semiconducting (S)-transition metal dichalcogenides (TMDs) and metallic (M)-TMDs via chemical vapor deposition (CVD) has emerged as a highly promising avenue for achieving low contact resistance in TMD-based devices. However, CVD-grown S–M heterostructures are mainly focused on non-degenerate semiconductors, despite degenerate semiconductors also being essential for semiconductor technology, such as negative differential resistance (NDR) device. In this study, a degenerate-S–M heterostructure, Nb-doped-WS₂–NbS₂, is synthesized via CVD with a liquid-metal precursor. Optimizing the growth parameters, such as growth temperature, precursor ratio, and H₂ content in the mixture gas, affords the desirable degenerate-Nb-doped-WS₂–NbS₂ heterostructure. Raman and photoluminescence spectroscopies, transmission electron microscopy, and energy-dispersive spectroscopy clearly clarify the doping signal and layer structure of the heterostructure. A growth mechanism has been proposed using in-plane and vertical models based on structural analysis. Electrical transport measurements reveal degenerate p-type behavior in the Nb-doped-WS₂. In the Nb-doped-WS₂–NbS₂ degenerate-S–M heterostructure, the device flows about twice as much on-state current as that by an Nb-doped-WS₂/Cr contact.