Synthesis of NbSe 2 /Bilayer Nb‐Doped WSe 2 Heterostructure from Exfoliated WSe 2 Flakes

Forming heterostructures of 2D metals and semiconductors using chemical vapor deposition (CVD) has significant potential to effectively reduce contact resistance in electronic devices. However, semiconducting transition metal dichalcogenide (TMD) layers in metal–semiconductor heterostructures are currently restricted to monolayers despite the superior mobility and density of states in bilayer TMDs. Herein, NbSe 2 /bilayer Nb‐doped WSe 2 metal/semiconductor heterostructure from exfoliated WSe 2 flakes are synthesized first. The exfoliated WSe 2 bulk crystals on an Nb‐coated substrate are heated to 950 °C under a flow of selenium vapor, and then the NbSe 2 /bilayer Nb‐doped WSe 2 heterostructures are formed. Statistics on the number of Nb‐doped WSe 2 layers grown on a 1 cm × 1 cm CVD substrate shows that 65% of the Nb‐doped WSe 2 layers are grown as bilayers. X‐ray photoelectron spectroscopy, optical microscopy, and transmission electron microscopy clearly clarify the number of Nb‐doped WSe 2 layers and heterostructure of NbSe 2 /bilayer Nb‐doped WSe 2 . Electrical measurements using Cr contacts show that bilayer Nb‐doped WSe 2 displays 7‐ and 10‐times higher mobility and on/off ratio than monolayer Nb‐doped WSe 2 . The mobility and on/off ratio are further doubled in NbSe 2 /bilayer Nb‐doped WSe 2 contact compared to Cr/bilayer Nb‐doped WSe 2 contact, attributed to a clean interface in vertical stack heterostructure, enhancing electrical performance.