Electronic structure, dynamic stability, elastic, and optical properties of MgTMN₂ (TM = Ti, Zr, Hf) ternary nitrides from first-principles calculations

Ternary nitride semiconductors with tunable electronic structure and charge transport properties have attracted increasing attention as optoelectronic materials. The recently discovered ternary $MgTMN2$ (⁠$TM=Ti,Zr,Hf$⁠) are predicted to be nondegenerate semiconductors with visible-range optical absorption onsets. In the present study, the electronic structure, elastic properties, optical absorption spectrum, and dynamic stability of the $MgTMN2$ system have been systematically studied by first-principles calculations based on the density functional theory. These compounds show semiconductor characteristics with a bandgap ranging from 1.0 to 1.5 eV predicted by the Heyd–Scuseria–Ernzerhof approach. Compared to the traditional semiconductors of Si and GaAs and III–V nitrides of GaN and AlN, these ternary nitrides have stronger resistance to external compression, shear strain, and deformation due to the larger elastic modulus. $MgTiN2$ shows a strong anisotropy characteristic along the $xy$ plane and $z$ axis, while for $MgZrN2$ and $MgHfN2$⁠, a weak elastic anisotropy is predicted. The absorption regions of these compounds are mainly concentrated in the ultraviolet region, and $MgTiN2$ is more sensitive to visible light with respect to the other two compounds. The thermodynamic stability of $MgTiN2$⁠, $MgZrN2$⁠, and $MgHfN2$ is verified by the stable phonon dispersion relations. It is found that the most stable low Miller index surface is (110) for $MgTiN2$ and (100) for $MgZrN2$ and $MgHfN2$⁠.