From the metal to the channel: a study of carrier injection through the metal/2D MoS₂interface

Abstract

Despite the fact that two-dimensional MoS films continue to be of interest for novel device concepts and beyond silicon technologies, there is still a lack of understanding on the carrier injection at metal/MoS interface and effective mitigation of the contact resistance. In this work, we develop a semi-classical model to identify the main mechanisms and trajectories for carrier injection at MoS contacts. The proposed model successfully captures the experimentally observed contact behavior and the overall electrical behavior of MoS field effect transistors. Using this model, we evaluate the injection trajectories for different MoS thicknesses and bias conditions. We find for multilayer (>2) MoS, the contribution of injection at the contact edge and injection under the contact increase with lateral and perpendicular fields, respectively. Furthermore, we identify that the carriers are predominantly injected at the edge of the contact metal for monolayer and bilayer MoS. Following these insights, we have found that the transmission line model could significantly overestimate the transfer length and hence the contact resistivity for monolayer and bilayer MoS. Finally, we evaluate different contact strategies to improve the contact resistance considering the limiting injection trajectory.

Impact of Device Scaling on the Electrical Properties of MoS2 Field-effect Transistors

“…Therefore, injection is only allowed from the edge of the metal contact directly into the carrier-rich channel, which is also predicted in other work 18,19 . For thicker MoS2 (more than 5 ML), the MoS2 region underneath the contact is no longer depleted and a longer section of the contact contributes to carrier injection 20,21,22 .…”

Effect of localized helium ion irradiation on the performance of synthetic monolayer MoS2 field-effect transistors

“…Ion beam pre-treatment of the contact region before metal deposition increases the concentration of dangling bonds available for molecular hybridization when the contact metal is deposited [ 32 ]. As we are treating an already hybridized interface, we suspect that the formation of point defects therein, such as migrated interstitials and antisite defects, will serve to trap carriers at the interface and will reduce the crowded injection current at the contact [ 43 ]. This may be empirically confirmed with a combination of low-temperature electrical characterization and capacitance measurements [ 44 – 45 ] in future work.…”

Analysis of black phosphorus double gate MOSFET using hybrid method for analogue/RF application

“…The main drawback of NEGF, it increases the computational cost for simulating three‐terminal devices. Also, it increases the complexity for non‐idealities study such as contact resistance, fermi level pinning, interface traps and ac analysis [12, 13]. Recently, Elahe Yarmoghaddam reported the physics‐based compact model for black phosphorus FETs at low drain voltages and this model to validate against long‐channel experimental results not for ballistic limit [14].…”