Investigating contact-limited scaling in sub-15-nm TMD FETs from first-principles

Abstract In this article, we present a first-principles field-effect transistors (FETs) contact study based on density functional theory and the non-equilibrium Green’s function method. We estimate device performance for three transition-metal-dichalcogenide (TMD) channel materials (WSe 2 , WS 2 , and MoS 2 ), including metal contacts (Ni) at source and drain for the first time. The results show that the variation in R c has less impact on I ON and I OFF at a given V DD than the variation in subthreshold swing ( SS ; with differences exceeding 30 mV/dec), suggesting SS may be more sensitive to the contacting material choice than previously realized at gate lengths below 15 nm. Among the channel and contact material combinations studied, Ni/WSe 2 FET leads to the best short-channel device performance. The quantum transport calculation shows the highest density of charge accumulation at the Ni/WSe 2 contact edge. Inspired by this first-principles study, we performed X-ray photoelectron spectroscopy and verified the bonding strength at the Ni/WSe 2 contact to be stronger than Ni/WS 2 and Ni/MoS 2 contacts. This supports the theoretical finding that the contact/channel materials need to be chosen to optimize SS and I ON in short-channel TMD FETs.