Yttrium-doping-induced metallization of molybdenum disulfide for ohmic contacts in two-dimensional transistors

The van der Waals systems could be used to overcome the issue of Fermi-level pinning in contacts of transistors based on two-dimensional semiconductors. However, the lack of advanced-node-lithography-compatible methods limits the use of such materials in wafer-scale integrated manufacturing. Here we report a yttrium-doping approach to convert semiconducting molybdenum disulfide (MoS2) into metallic MoS2. The approach, which is compatible with advanced-node wafer-scale integration, improves the band alignment and provides ohmic device contacts. It is based on a solid-state-source three-step doping method involving plasma, deposition and annealing, and can provide ångström-thickness surface doping. The yttrium-doped MoS2 acts as a metallic buffer that improves charge carrier transfer from the metal electrode to semiconducting MoS2. With this approach, we fabricate self-aligned, 10-nm-channel-length MoS2 field-effect transistors on two-inch wafers with an average contact resistances of 69 Ω µm and total resistances of 235 Ω µm. Our devices exhibit an ON-current density of 1.22 mA µm–1 at a drain voltage of 0.7 V, a ballistic ratio of 79% and a transconductance of 3.2 mS µm–1. A yttrium-doped metallic two-dimensional buffer layer can be used to improve charge carrier transport between the metal contacts and semiconductor channel in molybdenum-disulfide-based transistors.