Tunable Schottky Barrier and Efficient Ohmic Contacts in MSi₂N₄ (M = Mo, W)/2D Metal Contacts

Monolayer MSi₂N₄ (M = Mo, W) has been fabricated and proposed as a promising channel material for field-effect transistors (FETs) due to the high electron/hole mobility. However, the barrier between the metal electrode and MSi₂N₄ will affect device performance. Hence, it is desirable to reduce the barrier for achieving high-performance electrical devices. Here, using density functional theory (DFT) calculations, we systematically investigate the electrical properties of the van der Waals (vdW) contacts formed between MSi₂N₄ and two-dimensional (2D) metals (XY₂, X = Nb, Ta, Y = S, Se, Te). It is found that the contact types and Schottky barrier height (SBH) of MSi₂N₄/XY₂ can be effectively tuned by selecting 2D metals with different work functions (WFs). Specifically, n- and p-type Schottky contacts and Ohmic contacts can be achieved in MSi₂N₄/XY₂. Among them, MoSi₂N₄/H-NbS₂, WSi₂N₄/H-XS₂, and WSi₂N₄/H-NbSe₂ present Ohmic contacts due to the high WF of 2D metals. Notably, the pinning factors of MSi₂N₄/XY₂ are obviously larger than those of the other 2D semiconductor/metal contacts, indicating that the Fermi-level pinning (FLP) effect is weak in MSi₂N₄/XY₂. Therefore, vdW stack engineering can strongly weaken the FLP effect, making the Schottky barrier tunable in MSi₂N₄/XY₂ by choosing 2D metals with different WFs. The results provide important insights into the selection of appropriate electrodes and valuable guidance for the development of MSi₂N₄-based 2D electronic devices with high performance.