Monolayer XN2 (X Ti, Zr, Hf): Novel 2D materials with high stability, simultaneously high electron and hole mobilities from density functional theory

2D nitrides have attracted extensive attention because of their novel photoelectric properties and wide applications. In this work, we propose three novel 2D nitride materials, namely TiN2, ZrN2 and HfN2, and further systematically studied their stability, elastic property, electronic structure and thermal conductivity. The results show that the proposed monolayer XN2 (XTi, Zr, Hf) have high mechanical and dynamic stabilities. Furthermore, the monolayers are all direct bandgap semiconductors with band gaps of 1.87 eV, 2.00 eV and 2.69 eV, respectively. Based on deformation potential theory, it is found that the monolayers simultaneously have high hole and electron mobility at room temperature, up to 104–105 cm2 V−1 s−1. Also, due to the high group velocity and phonon lifetime, as well as volume specific heat capacity, monolayer XN2 (XTi, Zr, Hf) show high lattice thermal conductivity, as high as 41.80 W/m K, 60.22 W/m K and 56.88 W/m K, respectively. All these characteristics indicate that the proposed monolayer XN2 (XTi, Zr, Hf) have the potential to be applied in the fields of high-mobility polar semiconductors and photovoltaic devices in the future.