High mechanical strength and broad optical absorption in underexplored group IV nitride chalcogenides

Abstract

While lab-scale synthesis of trigonal-Zr₂N₂S, hexagonal-Zr₂N₂S and hexagonal-Zr₂N₂Se has been reported, meaningful data on the photophysical properties of IV-nitride chalcogenides in general are scarcely available. The first-principles calculations and genetic algorithm modeling in our work reveal the existence of remarkably stable, indirect gap trigonal-Zr₂N₂Se and trigonal-Hf₂N₂Se phases, which progress to direct gap, monoclinic materials in monolayer form. These structures display the desired optoelectronic properties, such as exceptionally high visible-UV absorption spectra (10⁵–10⁶ cm⁻¹) and exciton binding energy below 0.02 eV. Strong hybridization between the Zr-d, N-p and Se-p orbitals is accounted for by the polysilicon comparable Vickers hardness (10.64–12.77 GPa), while retaining ductile nature.