Monolayer C7N6 : Room-temperature excitons with large binding energies and high thermal conductivities

Two-dimensional (2D) carbon nitrides compounds have attracted wide attention in recent years due to their diverse structures and excellent electronic, thermal, and optical properties. Here, by using first-principles approach, we investigate in details the stability, many-body effect, electronic/thermal transport properties, and thermoelectric performance of monolayer C₇N₆ , as a new kind of 2D carbon nitride compounds composed of s p²-hybridized carbon atoms forming hexagonal lattice. Our results show that C₇N₆ monolayer is a direct band-gap semiconductor with a band-gap value of 3.56 eV under the accurate G₀W₀ method. Ab initio molecular dynamics simulations demonstrate that C₇N₆ maintains stable up to 1500 K . Two exciton absorption peaks can be observed within the band gap with the respective large binding energies of 0.84 and 0.09 eV , which means both excitons can exist at room temperature. Monolayer C₇N₆ possesses high carrier mobility with the order of 10²-10³cm²V^-1s^-1 . Moreover, we find that the lattice thermal conductivity for C₇N₆ is as high as 134.55 W /mK at room temperature, thus the thermoelectric figure of merit for C₇N₆ is relatively low. Our work suggests that C₇N₆ is a promising candidate for nanoscale (opto-)electronic and heat transport devices.