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

Abstract

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.

Computational Insights into Schottky Barrier Heights: Graphene and Borophene Interfaces with H- and H́-XSi2N4 (X = Mo, W) Monolayers

“…Previous studies have reported a Schottky to Ohmic contact transition in MS heterojunctions by applying several techniques such as electric field, doping, interlayer distance, altering the metal work function and strain engineering, thus achieving a tunneling probability of 100% by reducing the barrier width ( d TB ) to 0 eV . This Schottky to Ohmic transition has also been previously observed in graphene/MoSi 2 X 4 (X = N, P, and As) and MSi 2 N 4 /2D metal (M = Mo and W) vdW heterostructures. Based on these reports, applying electric field, strain engineering, and varying interlayer distance may tune the electric contact properties in studied heterostructures resulting in enhanced efficiency of nanoelectronic devices.…”

“…Based on these reports, applying electric field, strain engineering, and varying interlayer distance may tune the electric contact properties in studied heterostructures resulting in enhanced efficiency of nanoelectronic devices. Addressing the shift from Schottky to Ohmic contacts in these MS heterostructures can help regulate interfacial current flow and improve carrier transport probability for a variety of electronic applications. , …”

Ultralow Contact Resistance and Efficient Ohmic Contacts in MoGe2P4–Metal Contacts

“…Two-dimensional (2D) semiconductors, such as graphene, transition metal dichalcogenides (TMDs), and black phosphorene (BP), have exhibited potential applications in field effect transistors (FETs). − However, their practical applications still have some limitations, such as the zero-band gap in graphene, , poor environmental stability in BP, , and low carrier mobility in TMDs. , MoSi 2 N 4 and WSi 2 N 4 monolayers, recently synthesized by the chemical vapor deposition (CVD), have shown the potential to realize high-speed and low-power consumption devices due to the suitable band gap, high carrier mobility, and outstanding environmental stability. − Another MoSi 2 N 4 family material, the MoGe 2 P 4 monolayer, has attracted much attention due to its suitable band gap (0.5 eV) and outstanding carrier mobility (exceeding 10 3 cm 2 V –1 s –1 ), which is higher than those of the recently reported MoSi 2 N 4 /WSi 2 N 4 . Besides, the MoGe 2 P 4 monolayer is both dynamically and mechanically stable, which is much better than that of black phosphorene .…”