Electronic and optical properties of Y-doped Si₃N₄ by density functional theory

Highlights: • Y-doped α-Si₃N₄ and β-Si₃N₄ are systematically investigated by DFT. • Impacts of local structure and bond character on electronic property are studied. • Static dielectric constants and optical absorption properties are investigated. - Abstract: Geometry structures, formation energies, electronic and optical properties of Y-doped α-Si₃N₄ and β-Si₃N₄ are investigated based on the density functional theory (DFT). The low values of formation energies indicate both Y-doped Si₃N₄ models can be easily synthesized. Besides, the negative formation energies of α-Y_i-Si₃N₄ demonstrate that interstitial Y-doped α-Si₃N₄ has an excellent stability. The energies of impurity levels are different resulting from the different chemical environment around Y atoms. The impurity levels localized in the band gap reduces the maximum energy gaps, which enhances the optical properties of Si₃N₄. The static dielectric constants become larger and the optical absorption spectra show the red-shift phenomena for all Y-doped Si₃N₄ models