Devki Talwar, Department of Physics, coauthored “Structural and Dynamical Properties of Bridgman-grown Cd SexTe1−x ( 0 < x ≤ 0.35 ) Ternary Alloys” in the April 29, 2013, issue of Physical Review.
Measurements of the Raman scattering and extended x-ray-absorption fine-structure (EXAFS) spectroscopy are reported on a series of Bridgman-grown zinc-blende CdTe1−xSex (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 (TO1, LO1) and CdSe-like (TO2, LO2) pairs of optical phonons. The composition-dependent peak positions of the LO2 modes exhibited shifts towards the higher-energy side, while those of the LO1 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 CdTe1−xSex 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−1 in the low-temperature infrared reflectivity spectroscopy study to a SeTe localized vibrational mode.
Department of Physics