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 HfOx 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.