Quantum transport study of transition-metal dichalcogenide top-contacted geometries investigating the impact of nonuniform doping, dielectric environment, and image-force barrier lowering

Abstract

Computational studies on contacts between transition-metal dichalcogenides (TMDs) and metals generally focus on understanding the interface between metal and TMD using ab initio approaches such as density functional theory. However, the computational expense inherent in ab initio simulations limits their usage in simulating more realistic contacts with larger dimensions that include doping, dielectrics, back-gate and phenomena such as image-force barrier lowering (IFBL). In this work, we perform transport simulations to calculate contact resistance in top-contacted metal-MoS2 systems. We investigate the influence of spatially nonuniform doping in MoS2, metal workfunction, back-gate bias and the surrounding dielectric environment on contact resistance in metal-MoS2 contacts. We find that doping in the channel region plays a more critical role compared with doping in the overlap region. We also find that a low-kappa top dielectric greatly aids in reducing the tunneling barrier and therefore the contact resistance. Furthermore, we find that an addition of merely a few nanometers of low-kappa at the right edge of the overlap region is sufficient to significantly improve contact resistance. Finally, we highlight the importance of IFBL in transport simulations by comparing contact resistance with and without IFBL. Our results show that a low-kappa top dielectric, together with doping concentration greater than 1013 cm-2 in MoS2 and metal work- function less than 4.4 eV are simultaneously required to realize contact resistance of less than 1 kQ mu m in metal-MoS2 top contacts.