Impact of Rh, Ru, and Pd Leads and Contact Topologies on Performance of WSe 2 FETs: A First Comparative Ab Initio Study.

2D field-effect transistors (FETs) fabricated with transition metal dichalcogenide (TMD) materials are a potential replacement for the silicon-based CMOS. However, the lack of advancement in p-type contact is also a key factor hindering TMD-based CMOS applications. The less investigated path towards improving electrical characteristics based on contact geometries with low contact resistance ( R C ) has also been established. Moreover, finding contact metals to reduce the R C is indeed one of the significant challenges in achieving the above goal. Our research provides the first comparative analysis of the three contact configurations for a WSe 2 monolayer with different noble metals (Rh, Ru, and Pd) by employing ab initio density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. From the perspective of the contact topologies, the R C and minimum subthreshold slope ( SS MIN ) of all the conventional edge contacts are outperformed by the novel non-van der Waals (vdW) sandwich contacts. These non-vdW sandwich contacts reveal that their R C values are below 50 Ω∙μm, attributed to the narrow Schottky barrier widths (SBWs) and low Schottky barrier heights (SBHs). Not only are the R C values dramatically reduced by such novel contacts, but the SS MIN values are lower than 68 mV/dec. The new proposal offers the lowest R C and SS MIN , irrespective of the contact metals. Further considering the metal leads, the WSe 2 /Rh FETs based on the non-vdW sandwich contacts show a meager R C value of 33 Ω∙μm and an exceptional SS MIN of 63 mV/dec. The two calculated results present the smallest-ever values reported in our study, indicating that the non-vdW sandwich contacts with Rh leads can attain the best-case scenario. In contrast, the symmetric convex edge contacts with Pd leads cause the worst-case degradation, yielding an R C value of 213 Ω∙μm and an SS MIN value of 95 mV/dec. While all the WSe 2 /Ru FETs exhibit medium performances, the minimal shift in the transfer curves is interestingly advantageous to the circuit operation. Conclusively, the low- R C performances and the desirable SS MIN values are a combination of the contact geometries and metal leads. This innovation, achieved through noble metal leads in conjunction with the novel contact configurations, paves the way for a TMD-based CMOS with ultra-low R C and rapid switching speeds.