A graphene-like Mg₃N₂ monolayer: high stability, desirable direct band gap and promising carrier mobility

Based on density functional calculations and a global particle-swarm optimization method, a novel Mg₃N₂ monolayer (g-Mg₃N₂) with a hexagonal lattice was firstly predicted, displaying an intrinsic direct band gap of 1.86 eV, close to that (1.90 eV) of a MoS₂ monolayer. In the infinite planar geometry, each N atom adopts sp² hybridization with three Mg atoms and each Mg atom as a 2-fold coordinated "bridge" enables the stable bonding with two N atoms. Such a g-Mg₃N₂ sheet is not only dynamically stable, but also can withstand temperatures up to 2000 K. Importantly, the intrinsic acoustic-phonon-limited carrier mobility of the g-Mg₃N₂ sheet can reach ∼10³ cm² V^-1 s^-1 for electrons and ∼433 cm² V^-1 s^-1 for holes under ambient conditions, higher than that (60-200 cm² V^-1 s^-1) of MoS₂ and comparable to that (∼10³ cm² V^-1 s^-1) of few-layer phosphorene. In particular, the derivative nanotubes have direct band gaps, independent of chirality and radius. The versatility of g-Mg₃N₂ and its derivatives is expected to possess a broad range of applications in FET devices.