Finite-bias first-principles calculations of contact resistance of transition metal dichalcogenides

Despite the tremendous amount of experimental and theoretical efforts to achieve the low contact resistance between metal electrodes and transition metal dichalcogenide (TMDC) semiconductors, a critical issue in developing TMDC-based electronic and optoelectronic devices, the atomic-scale understanding of metal-TMDC interfaces is still incomplete. In this study, adopting the junction models based on the Ag/MoS₂ top- and edge-contact models, we perform equilibrium density functional theory (DFT) and finite-bias multi-space DFT calculations [1,2] and extract contact resistance values at different TMDC channel lengths. From finite-bias calculations, we identify the transitions in the contact resistance scaling with the increase of the channel length and find that they result from the transition from the regime where Ag metal-induced gap states dominate the charge injection to that where the conduction band edge states of the MoS₂ channel contribute to the charge transport. Such transition behavior cannot be observed, indicating a critical missing ingredient of the previous first-principles studies of TMDC contact resistance. Quantitatively, the finite-bias contact resistance value of the Ag/MoS₂ top contact is found to be lower than that of the Ag/MoS₂ edge contact. However, considering the Ag/WSe₂ top- and Ag-WSe₂ edge-contact models, we obtain an opposite conclusion, which indicates that the optimal contact geometry for TMDCs can be different depending on the metal-TMDC material combination. This work clarifies many contradicting conclusions in the literature and provides theoretical guidelines for designing low-resistance metal-TMDC contact.

[1] J. Lee, H. Yeo, and Y.-H. Kim, Proc. Nat. Acad. Sci. 117, 10142-10148 (2020).

[2] J. Lee, H.S.Kim, and Y.-H. Kim, Adv. Sci. 7, 2001038 (2020).