Structural and dynamical properties of Bridgman-grown Cd SexTe1−x ( 0 < x ≤ 0.35 ) ternary alloys
Devki N. Talwar Department of Physics,
Indiana University of Pennsylvania, 975 Oakland Avenue, 56 Weyandt Hall,
Indiana, Pennsylvania 15705-1087, USA
Zhe Chuan Feng Institute of Photonics and
Optoelectronics, Department of Electrical Engineering, and Center for
Emerging Material and Advanced Devices, National Taiwan University,
Taipei 106-17, Taiwan, Republic of China
Jyh-Fu LeeNational Synchrotron Radiation Research Center, Hsinchu 300-76, Taiwan, Republic of China
P. Becla Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
Received 15 August 2012; revised 20 November 2012; published 29 April 2013
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 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.
Phys. Rev. B
87,
165208
(2013)
[12 pages]