Structural and dynamical properties of Bridgman-grown CdSe[subscript x]Te[subscript 1−x] (0<x≤0.35) ternary alloys

Abstract

Measurements of the Raman scattering and extended x-ray-absorption fine-structure (EXAFS) spectroscopy are reported on a series of Bridgman-grown zinc-blende CdTe[subscript 1−x]Se[subscript x] (0.35 ≥ x > 0.05) ternary alloys to empathize their lattice dynamical and structural properties. Low-temperature Raman spectra have revealed the classic CdTe-like (TO[subscript 1], LO[subscript 1]) and CdSe-like (TO[subscript 2], LO[subscript 2]) pairs of optical phonons. The composition-dependent peak positions of the LO[subscript 2] modes exhibited shifts towards the higher-energy side, while those of the LO[subscript 1] phonon frequencies have unveiled the slight redshifts. Detailed analyses of EXAFS data by using the first-principles bond orbital model have enabled us to estimate both the lattice relaxations and nearest-neighbor radial force constants around the Se/Te atoms in the CdTe/CdSe matrix. These results are methodically integrated in the “average t-matrix” formalism within the Green's-function theory for defining the impurity perturbations to comprehend the composition-dependent optical phonons in CdTe[subscript 1−x]Se[subscript x] alloys. Based on our comprehensive calculations of impurity modes in the low-composition regime x → 0, we have assigned the weak phonon feature observed near ∼175 cm[superscript −1] in the low-temperature infrared reflectivity spectroscopy study to a Se[subscript Te] localized vibrational mode.