Optical Study of Filled Tetrahedral Compounds Li_(3)AlN_(2) and Li_(3)GaN_(2)

摘要

A detailed analysis of the optical properties of filled tetrahedral semiconductors Li_(3)AlN_(2) and Li_(3)GaN_(2) has been performed, using the full potential line-arized augmented plane wave method within the density functional theory. The real and imaginary parts of the dielectric function epsilon(omega), the optical absorption coefficient I(omega), the reflectivity R(omega), and the electron energy loss function are calculated within the random phase approximation. The inter-band 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 Li_(3)GaN_(2). In the Li_(3)AlN_(2) 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 Be_(3)N_(2) in the same structure [space group Ia3(206)] are included in this work.