Analyzing the Effect of High-k Dielectric-Mediated Doping on Contact Resistance in Top-Gated Monolayer MoS₂ Transistors

A scalable process that can yield low-resistance contacts to transition metal dichalcogenides is crucial for realizing a viable device technology from these materials. Here, we systematically examine the effect of high-k dielectric-mediated doping on key device metrics including contact resistance and carrier mobility. Specifically, we use top-gated transistors from monolayer MoS₂ as a test vehicle and vary the MoS₂ doping level by adjusting the amount of oxygen vacancies in the HfO_x gate dielectric. To understand the effect of doping on the contact resistance, from a fundamental standpoint, we first estimate the doping level in monolayer MoS₂. The results of our device studies quantitatively show that the reduction in contact resistance with an increase in doping is due to the doping-induced lowering of the Schottky barrier height (SBH) at the metal-semiconductor interface. Furthermore, our temperature-dependent measurements reveal that a mixture of thermionic and field emissions, even at high carrier densities, dominates carrier conduction at the contact. While our study reveals the effectiveness of dielectric-induced doping in lowering SBH, it suggests that a further reduction of SBH using alternative methods is necessary for achieving an ohmic-like contact to monolayer MoS₂.