Lattice vibrations of Zn$_{1-x}$Cd$_x$Se semiconductor alloy in the two-mode and percolation models of rearrangement of the vibrational spectrum with the composition

The lattice-vibration spectra of (Zn,Cd)Se and Zn(Se,Te) alloy crystals are considered together. The rearrangement of vibrational modes of the crystals under variations in the alloy composition is interpreted within the context of the two-mode (1-bond $\to$ 1-mode) and percolation (1-bond $\to$ 2-mode) models. In (Zn,Cd)Se alloys of any composition, the lattice vibration modes are distributed in frequency in accordance with the two-mode type of behavior and can be divided into ZnSe- and CdSe-like vibrations and one complimentary low-intensity mode. In the percolation model of rearrangement of the vibrational spectra of the alloy, the complementary mode is a consequence of the composite character of the alloy formed with natural local fluctuations of the alloy composition in accordance with percolation theory. The complementary mode is not associated with defects; in contrast, it is a derivative of the principal mode of ZnSe-like vibrations. The optical vibration spectrum of the (Zn,Cd)Se alloy consists of a single CdSe-like vibrational mode and a percolation doublet of ZnSe-like vibrational modes.