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

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-Yi-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.