Understanding\nthe Impact of Contact-Induced Strain\non the Electrical Performance of Monolayer WS<sub>2</sub> Transistors

Two-dimensional (2D) electronics require low contact\nresistance\n(<i>R</i><sub>C</sub>) to approach their fundamental limits.\nWS<sub>2</sub> is a promising 2D semiconductor that is often paired\nwith Ni contacts, but their operation is not well understood considering\nthe nonideal alignment between the Ni work function and the WS<sub>2</sub> conduction band. Here, we investigate the effects of contact\nsize on nanoscale monolayer WS<sub>2</sub> transistors and uncover\nthat Ni contacts impart stress, which affects the WS<sub>2</sub> device\nperformance. The strain applied to the WS<sub>2</sub> depends on contact\nsize, where long (1 μm) contacts (<i>R</i><sub>C</sub> ≈ 1.7 kΩ·μm) show a 78% reduction in <i>R</i><sub>C</sub> compared to shorter (0.1 μm) contacts\n(<i>R</i><sub>C</sub> ≈ 7.8 kΩ·μm).\nWe also find that thermal annealing can relax the WS<sub>2</sub> strain\nin long-contact devices, increasing <i>R</i><sub>C</sub> to 8.5 kΩ·μm. These results reveal that thermo-mechanical\nphenomena can significantly influence 2D semiconductor–metal\ncontacts, presenting opportunities to optimize device performance\nthrough nanofabrication and thermal budget.