One-Step Synthesis of NbSe/Nb-Doped-WSe Metal/Doped-Semiconductor van der Waals Heterostructures for Doping Controlled Ohmic Contact.

van der Waals heterostructures (vdWHs) of metallic (m-) and semiconducting (s-) transition-metal dichalcogenides (TMDs) exhibit an ideal metal/semiconductor (M/S) contact in a field-effect transistor. However, in the current two-step chemical vapor deposition process, the synthesis of m-TMD on pregrown s-TMD contaminates the van der Waals (vdW) interface and hinders the doping of s-TMD. Here, NbSe/Nb-doped-WSe metal-doped-semiconductor (M/d-S) vdWHs are created via a one-step synthesis approach using a niobium molar ratio-controlled solution-phase precursor. The one-step growth approach synthesizes Nb-doped WSe with a controllable doping concentration and metal/doped-semiconductor vdWHs. The hole carrier concentration can be precisely controlled by controlling the Nb/(W + Nb) molar ratio in the precursor solution from ∼3 × 10/cm at Nb-0% to ∼1.38 × 10/cm at Nb-60%; correspondingly, the contact resistance value decreases from 10 888.78 at Nb-0% to 70.60 kΩ.μm at Nb-60%. The Schottky barrier height measurement in the Arrhenius plots of ln(/) versus / demonstrated an ohmic contact in the NbSe/WNbSe vdWHs. Combining p-doping in WSe and M/d-S vdWHs, the mobility (27.24 cm V s) and on/off ratio (2.2 × 10) are increased 1238 and 4400 times, respectively, compared to that using the Cr/pure-WSe contact (0.022 cm V s and 5 × 10, respectively). Together, the value using the NbSe contact shows 2.46 kΩ.μm, which is ∼29 times lower than that of using a metal contact. This method is expected to guide the synthesis of various M/d-S vdWHs and applications in future high-performance integrated circuits.