Abstract

Exploring novel materials with superior properties is of a great significance for potential applications in future electronics and optoelectronics. Based on first-principles calculations, we predict new two-dimensional (2D) group-IV carbides containing isolated C2 dimers rather than individual carbon atoms, offering novel properties for nanoelectronics. The 2D carbides, namely th-XC2 (X = Si, Ge, Sn, and so on), are not only dynamically, mechanically, and thermally stable, but also exhibit exceptional properties such as anisotropic elasticity, ideal strength, and tunable phononic band gap. Moreover, they are all narrow direct band gap semiconductors with band gaps up to ∼0.9 eV, which can be continuously tuned by strain and alloy engineering. They show excellent transport properties including strong anisotropic and small electron/hole effective mass and ultrahigh carrier mobilities (up to ∼105cm2V−1s−1). Excitingly, the anisotropy of the hole effective mass can be rotated by 90∘ simply via alloying X element in tetrahexagonal carbon (th-C). Thus, the intrinsic carrier mobility in th-C is significantly enhanced by not only strain but also alloy engineering. In short, the 2D carbides are unique as composed of C2 dimers with novel properties making them promising for nanoelectronics.