Understanding the Impact of Contact-Induced Strain on the Electrical Performance of Monolayer WS<sub>2</sub> Transistors
Lauren Hoang, Marc Jaikissoon, Çağıl Köroğlu, Zhepeng Zhang, Robert K. A. Bennett, Jung‐Hwan Song, Jerry A. Yang, Jung-Soo Ko, Mark L. Brongersma, Krishna C. Saraswat, Eric Pop, Andrew J. Mannix
Abstract
High Resolution Image Download MS PowerPoint Slide Two-dimensional (2D) electronics require low contact resistance ( R C ) to approach their fundamental limits. WS 2 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 2 conduction band. Here, we investigate the effects of contact size on nanoscale monolayer WS 2 transistors and uncover that Ni contacts impart stress, which affects the WS 2 device performance. The strain applied to the WS 2 depends on contact size, where long (1 μm) contacts ( R C ≈ 1.7 kΩ·μm) show a 78% reduction in R C compared to shorter (0.1 μm) contacts ( R C ≈ 7.8 kΩ·μm). We also find that thermal annealing can relax the WS 2 strain in long-contact devices, increasing R C 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.