Electrical\nContacts in Monolayer MoSi₂N₄ Transistors

Abstract

The\nlatest synthesized monolayer (ML) MoSi₂N₄ material\nexhibits stability in ambient conditions, suitable bandgap,\nand high mobilities. Its potential as a next-generation transistor\nchannel material has been demonstrated through quantum transport simulations.\nHowever, in practical two-dimensional (2D) material transistors, the\nelectrical contacts formed by the channel and the electrode must be\noptimized, as they are crucial for determining the efficiency of carrier\ninjection. We employed the density functional theory (DFT) combined\nwith the nonequilibrium Green’s function (NEGF) method to systematically\nexplore the vertical and horizontal interfaces between the typical\nmetal electrodes and the ML MoSi₂N₄. The DFT+NEGF\nmethod incorporates the coupling between the electrode and the channel,\nwhich is crucial for quantum transport. Among these metals, Sc and\nTi form <i>n</i>-type Ohmic contacts with zero tunneling\nbarriers at both vertical and horizontal interfaces with ML MoSi₂N₄, making them optimal for contact metals. In-ML\nMoSi₂N₄ contacts display zero Schottky barriers\nbut a 3.11 eV tunneling barrier. Cu and Au establish <i>n</i>-type Schottky contacts, while Pt forms a <i>p</i>-type\ncontact. The Fermi pinning factors of the metal-ML MoSi₂N₄ contacts for both electrons and holes are above 0.51,\nmuch higher than the typical 2D semiconductors. Moreover, there is\na strong positive correlation between the Fermi pinning factor and\nthe band gap, with a Spearman rank correlation coefficient of 0.897\nand a <i>p</i>-value below 0.001. Our work provides insight\ninto the contact optimization for the ML MoSi₂N₄ transistors and highlights the promising potential of ML MoSi₂N₄ as the channel material for the next-generation\nFETs.