Understanding the Impact of Contact-Induced Strain on the Electrical Performance of Monolayer WS Transistors.

Two-dimensional (2D) electronics require low contact resistance () to approach their fundamental limits. WS is a promising 2D semiconductor that is often paired with Ni contacts, but their operation is not well understood considering the nonideal alignment between the Ni work function and the WS conduction band. Here, we investigate the effects of contact size on nanoscale monolayer WS transistors and uncover that Ni contacts impart stress, which affects the WS device performance. The strain applied to the WS depends on contact size, where long (1 μm) contacts ( ≈ 1.7 kΩ·μm) show a 78% reduction in compared to shorter (0.1 μm) contacts ( ≈ 7.8 kΩ·μm). We also find that thermal annealing can relax the WS strain in long-contact devices, increasing to 8.5 kΩ·μm. These results reveal that thermo-mechanical phenomena can significantly influence 2D semiconductor-metal contacts, presenting opportunities to optimize device performance through nanofabrication and thermal budget.