Raman scattering from the filled tetrahedral semiconductor LiZnAs

The bonding character in the filled tetrahedral semiconductor LiZnAs (space group, F4-3m), which can be naturally interpreted as a zinc-blende-like (ZnAs)(-) lattice stoichiometrically filled with He-like Li+ interstitials, is studied using a Raman-scattering method. Two longitudinal-optical (LO) and transverse-optical (TO) phonons at k similar to 0 (Gamma point) for Li-As and Zn-As pairs are observed at 452 and 420 cm(-1) and 233 and 204 cm(-1), respectively. The macroscopic transverse effective charge e(T)(*) estimated from the separation of the LO and TO branches at k similar to 0 for Li-As pair is less than that for Zn-As pair, showing the relatively high ionicity of the Li-As bond, whereas the force constant of Zn-As is about 23% higher than that of Li-As, showing the relatively high covalency of Zn-As bond. In comparison with the e(T)(*) values of Zn-As bond in LiZnAs and Ga-As bond in GaAs, the covalency of Zn-As bond is comparable with that of Ga-As bond.