Electrical Contacts in Monolayer MoSi2N4 Transistors.

ABSTRACT

The latest synthesized monolayer (ML) MoSi2N4 material exhibits stability in ambient conditions, suitable bandgap, and high mobilities. Its potential as a next-generation transistor channel material has been demonstrated through quantum transport simulations. However, in practical two-dimensional (2D) material transistors, the electrical contacts formed by the channel and the electrode must be optimized, as they are crucial for determining the efficiency of carrier injection. We employed the density functional theory (DFT) combined with the nonequilibrium Green's function (NEGF) method to systematically explore the vertical and horizontal interfaces between the typical metal electrodes and the ML MoSi2N4. The DFT+NEGF method incorporates the coupling between the electrode and the channel, which is crucial for quantum transport. Among these metals, Sc and Ti form n-type Ohmic contacts with zero tunneling barriers at both vertical and horizontal interfaces with ML MoSi2N4, making them optimal for contact metals. In-ML MoSi2N4 contacts display zero Schottky barriers but a 3.11 eV tunneling barrier. Cu and Au establish n-type Schottky contacts, while Pt forms a p-type contact. The Fermi pinning factors of the metal-ML MoSi2N4 contacts for both electrons and holes are above 0.51, much higher than the typical 2D semiconductors. Moreover, there is a strong positive correlation between the Fermi pinning factor and the band gap, with a Spearman rank correlation coefficient of 0.897 and a p-value below 0.001. Our work provides insight into the contact optimization for the ML MoSi2N4 transistors and highlights the promising potential of ML MoSi2N4 as the channel material for the next-generation FETs.