Lattice Dynamics of Zn-Cd Chalcogenides—A Critical-Point Analysis

The frequency—wave-vector dispersion relations for the normal modes of vibrations for zinc and cadmium tellurides, crystallizing in the zinc-blende crystal structure, have been calculated in the framework of the second-neighbor-ionic model. The frequencies of four critical-point phonons [$\mathrm{LO}\left(\Gamma \right)$, $\mathrm{TO}\left(\Gamma \right)$, $\mathrm{LO}\mathrm{}\left(X\right)\mathrm{}$, and $\mathrm{TA}\mathrm{}\left(X\right)\mathrm{}$] obtained by infrared- and Raman-scattering measurements and the three elastic constants $c_{11}$, $c_{12}$, and $c_{44}$ have been employed as input data so as to calculate the involved seven lattice-dynamical model parameters. Absorption maxima in the infrared and/or second-order Raman-scattering experiments have been tentatively assigned by an extensive use of the lattice-dynamical-calculated critical phonons. The calculated phonon frequencies show a reasonably satisfactory agreement with the available optical data.