ELECTRONIC STRUCTURES AND OPTICAL PROPERTIES OF 2Al-AND 2Ca-DOPED β-Si3N4: A FIRST-PRINCIPLES STUDY

First-principles calculations have been conducted to study the electronic structures and optical properties of 2Al- and 2Ca-doped beta-Si3N4. Calculated formation energies of 2Al- and 2Ca-doped systems are 5.9745 eV and 18.9376 eV, respectively, indicating the former has a stable structure than the latter. The band gaps of two systems are 3.1573 eV and 2.0155 eV, respectively, reveals that the band structures of them behave like semiconductors. The static dielectric constants of two systems are 40 and 37, respectively, which denotes their potential applications in electronics and optics. The strong absorption bands ranging from 4 eV to 16 eV become much sharper and show a red-shift after doping. The offset of 2Al-doped system is larger than that of 2Ca-doped system. The absorption coefficient can be remarkably modulated by doping. In calculated frequency-dependent electron energy loss spectra (EELS) of doping systems, the host peaks all locate at about 15 eV.