Fundamental and second-order phonon processes in CdTe and ZnTe

Fundamental and higher-order photon-phonon interactions dominate the far infrared absorption and dispersion spectrum of most semiconductors and dielectrics. We present a detailed investigation of the temperature dependence of the dielectric function of the important II-VI semiconductors CdTe and ZnTe in the frequency range below 3 THz, between 10 and 300 K. From the dielectric function we determine the temperature dependence of the fundamental transverse-optical ~TO! frequency in CdTe and ZnTe as well as the TO phonon damping rate in CdTe, and the dynamic ionic charge of both crystals is inferred from the measurements. Furthermore, our experimental data enable unambiguous assignment of low-frequency absorption bands to sum and difference combinations of fundamental phonon modes at critical points away from the Brillouin zone center.