Although many prototype devices based on two-dimensional (2D) MoS₂ have been fabricated and wafer scale growth of 2D MoS₂ has been realized, the fundamental nature of 2D MoS₂-metal contacts has not been well understood yet. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS₂-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS₂ due to a charge transfer. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS₂-Sc interface. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS₂-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. BL MoS₂-metal contacts generally have a reduced SBH than ML MoS₂-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency.

By using first-principles calculations, we predict that a sizable band gap can be opened at the Dirac point of silicene without degrading silicene's electronic properties with n-type doping by Cu, Ag, and Au adsorption, p-type doping by Ir adsorption, and neutral doping by Pt adsorption. A silicene p–i–n tunneling field effect transistor (TFET) model is designed by the adsorption of different transition metal atoms on different regions of silicene. Quantum transport simulations demonstrate that silicene TFETs have an on–off ratio of 10³, a small sub-threshold swing of 77 mV dec⁻¹, and a large on-state current of over 1 mA μm⁻¹ under a supply voltage of about 1.7 V.

Recently, constructing van der Waals (vdW) heterojunctions by stacking different two-dimensional (2D) materials has been considered to be effective strategy to obtain the desired properties. Here, through first-principles calculations, we find theoretically that the 2D $n$-InSe/$p$-GeSe(SnS) vdW heterojunctions are the direct-band-gap semiconductor with typical type-II band alignment, facilitating the effective separation of photogenerated electron and hole pairs. Moreover, they possess the high optical absorption strength ($\sim {10}^5$), broad spectrum width, and excellent carrier mobility ($\sim {10}^3\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$). Interestingly, under the influences of the interlayer coupling and external electric field, the characteristics of type-II band alignment is robust, while the band-gap values and band offset are tunable. These results indicate that 2D $n$-InSe/$p$-GeSe(SnS) heterojunctions possess excellent optoelectronic and transport properties, and thus can become good candidates for next-generation optoelectronic nanodevices.