Optical Study of Filled Tetrahedral Compounds Li3AlN2 and Li3GaN2

Abstract

A detailed analysis of the optical properties of filled tetrahedral semiconductors Li3AlN2 and Li3GaN2 has been performed, using the full potential linearized augmented plane wave method within the density functional theory. The real and imaginary parts of the dielectric function e(ω), the optical absorption coefficient I(ω), the reflectivity R(ω), and the electron energy loss function are calculated within the random phase approximation. The interband transitions responsible for the structures in the spectra are specified. Looking at optical matrix element, we note that the major peaks are dominated by transition from metal s, N 2p states to N 2p, Ga 3d states. The theoretical calculated optical properties and electron energy loss spectrum yield a static dielectric constant of 5.34 and a plasmon energy of 19.47 eV for Li3GaN2. In the Li3AlN2 compound, the static dielectric constant decreases to 4.75 and yields a plasmon energy of 18.5 eV. The effect of spin–orbit coupling on the optical properties is also investigated and found to be quite small, especially in the low-energy region. In order to check the reliability of our calculations, analogous results obtained for Be3N2 in the same structure [space group Ia3(206)] are included in this work.