Optical Phonons in ZnGeP2 and CdGeP2

The phonon spectra of ZnGeP2 and CdGeP2, determined by Raman scattering on single crystals at room and liquid nitrogen temperature, are presented. The close coincidence of the zone center phonon energies of ZnGeP2 with the corresponding τ, X, and W modes of its isoelectronic analogue, GaP, bears out the expected similarity of lattice vibrations in ternary chalcopyrite compounds and binary zincblende materials. Differences between ZnGeP, and CdGeP2 can be attributed to mass and force constant differences when Zn is substituted by the heavier Cd atom.