HfN₂ monolayer: A new direct-gap semiconductor with high and anisotropic carrier mobility

Searching for two-dimensional (2D) stable materials with direct band gap and high carrier mobility has attracted great attention for their electronic device applications. Using the first principles calculations and particle swarm optimization (PSO) method, we predict a new 2D stable material (HfN₂ monolayer) with the global minimum of 2D space. The HfN₂ monolayer possesses direct band gap (~1.46 eV) and it is predicted to have high carrier mobilities (~10³ cm²·V^-1·s^-1) from deformation potential theory. The direct band gap can be well maintained and flexibly modulated by applying an easily external strain under the strain conditions. In addition, the newly predicted HfN₂ monolayer possesses good thermal, dynamical, and mechanical stabilities, which are verified by ab initio molecular dynamics simulations, phonon dispersion and elastic constants. These results demonstrate that HfN₂ monolayer is a promising candidate in future microelectronic devices.