Electronic structures and optical properties of γ-Si3N4 doped with La

The crystal structures, electronic structures and optical properties of γ-Si3N4 doped with La are studied using the plane-wave pseudo-potential method (PWP) based upon the density functional theory with Perdew-Wang 91 (PW91) generalized gradient approximation (GGA). The calculated band gap of doping γ-Si3N4 was found to significantly decrease after the introduction of La. The band structures of γ-Si3N4 behave like semiconductors for low La concentration and metal for high La concentration. The calculated optical properties showed that the static dielectric constant of γ-Si3N4 doped with La is much higher than that of undoped γ-Si3N4, so it may act as a new dielectric and refractive material.