First principles calculations of electronic structures and optical properties of Al- and Ca-doped β-Si₃N₄

Abstract

The crystal structures, formation energies, electronic structures and optical properties of Al- and Ca-doped β-Si₃N₄ were studied using first principles calculations based on density functional theory within the generalised gradient approximation. Results show that the band gaps E_g of Al- and Ca-doped β-Si₃N₄ decrease distinctly in comparison to that of β-Si₃N₄. The band structures of Ca-doped supercell behave like semiconductors. The binding energy E_b and formation energy E_f of β-Si₃N₄ doped with Al are lower than those of Ca-doped β-Si₃N₄, indicating that the former has a more stable crystal structure than the latter. The static dielectric constant ϵ(0) increases significantly to ∼35 after Al doping and almost does not change after Ca doping. The strong absorption band located at 5·11–20·81 eV becomes much sharper and shows a red shift after Al and Ca doping. The offset of the Al-doped system is larger than that of the Ca-doped system. The absorption coefficient can be remarkably modulated by Al and Ca doping, indicating the potential applications of Al- and Ca-doped β-Si₃N₄ in optical system.

Keywords:

• First principles
• Electronic structures
• Optical properties
• β-Si₃N₄
• Doping

Acknowledgement

The work was supported by the National Natural Science Foundation of China (grant no. 90816018).