Two-dimensional ScN with high carrier mobility and unexpected mechanical properties

Two-dimensional (2D) semiconductors with desirable bandgaps and high carrier mobility have great potential in electronic and optoelectronic applications. In the present work, 2D M-ScN, H-ScN, and O-ScN are predicted by the swarm-intelligent global structure search method. The low formation energies and high dynamical and thermal stabilities indicate the high feasibility of experimental synthesis of these ScN monolayers. The electronic structure calculations reveal that M-ScN and O-ScN are both direct bandgap semiconductors with the bandgaps of 1.39 and 2.14 eV, respectively, while H-ScN has a large indirect bandgap of 3.21 eV. In addition, both M-ScN and H-ScN exhibit ultra-high electron mobilities (3.09 × 10⁴ cm² V^-1 s^-1 and 1.22 × 10⁴ cm² V^-1 s^-1, respectively). More notably, O-ScN is found to be a promising 2D auxetic and ferroelastic material. The values of negative Possion's ratios and reversible strain of this monolayer are predicted to be -0.27% and 15%, respectively.