Structural and dynamical properties of Bridgman-grown CdSexTe1−x(0<x≤

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 1−x Se 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 1 , LO 1) and CdSe-like (TO 2 , LO 2) pairs of optical phonons. The composition-dependent peak positions of the LO 2 modes exhibited shifts towards the higher-energy side, while those of the LO 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 1−x Se 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 −1 in the low-temperature infrared reflectivity spectroscopy study to a Se Te localized vibrational mode.

Polarization Dependent Reflectivity and Transmission for Cd1-Xznxte/GaAs(001) Epifilms in the Far-Infrared and Near-Infrared to Ultraviolet Region

“…The derived optical parameters n, k and ε 1 , ε 2 are included in Figures 2b and 2c, ) at n = k with 1 ( ) ε ω = 0. For Cd 1-x Zn x Te alloy [9] with x = 0.2, the analysis of our FIR reflectivity spectra (Figure 3a) at near normal incidence offered optical parameters (Figures 3b and 3c) in excellent affirmation to the RS results [14] revealing CdTe-like (TO 1 , LO 1 ) and ZnTe-like (TO 2 , LO 2 ) modes. Not only these observations provided strong corroboration to the polarization dependent results (Figure 3d) but are also found consistent with the recent elucidations of the two-phonon-mode behavior predicted by RS and modified random element iso-displacement (MREI) model [8][9][10].…”

“…The results when analyzed by a classical method envisioned a "two-phonon-mode" behavior. Recently, we have performed extensive micro-Raman and extended X-ray absorption fine-structure (EXAFS) measurements on the Bridgman-grown Cd 1-x Zn x Te alloyed samples [14,15] in the entire composition range 1.0 ≥ x ≥ 0.0 and comprehended their phonon and structural traits. A careful evaluation of the experimental data by an average-t-matrix Green's function (ATM-GF) approach has authenticated the "twophonon mode" stance [14].…”

“…Recently, we have performed extensive micro-Raman and extended X-ray absorption fine-structure (EXAFS) measurements on the Bridgman-grown Cd 1-x Zn x Te alloyed samples [14,15] in the entire composition range 1.0 ≥ x ≥ 0.0 and comprehended their phonon and structural traits. A careful evaluation of the experimental data by an average-t-matrix Green's function (ATM-GF) approach has authenticated the "twophonon mode" stance [14]. While the composition-dependent EXAFS data revealed a bimodal distribution of nearest-neighbor bond lengthstheoretical analysis by first-principles bond-orbital model permitted an accurate appraisal of the lattice relaxations around Zn/Cd atoms in CdTe/ZnTe materials.…”

“…One must note that only limited efforts have been made by SE to uncover the optical properties of CZT alloys in the near-IR (NIR) to ultraviolet (UV) energy range [16][17][18][19][20]. From a theoretical stand point, it has now become possible [14,15] to expend pragmatic model dielectric functions (MDFs) of binary materials to elucidate structural and optical characteristics of semiconducting ternary alloys, and SLs grown on different substrates. Earlier, it was comprehended that only first principles methods could yield material characteristics with accuracies required of the experiments [21].…”

STRUCTURAL AND OPTICAL PROPERTIES IN NEAR INFRARED OF CdTeSe COLOIDAL QUANTUM DOTS FOR POTENTIAL APPLICATION IN SOLAR CELLS

“…When the temperature is increased to 280 o C, most of the Te ions would have reacted, and Se ions would keep linked with Cd ions creating many Cd-Se bonds, shrinking the crystal lattice structure in the same tendency with zb-CdSe and shifting diffraction lines towards angles 2θ higher -as observed on the XRD patterns of sample created at 280 o C. Figure 2 is the Raman spectra of CdTeSe QD samples fabricated at different temperatures recorded with the micro Raman XploRa Plus using 532 nm laser as an excitation source. On the Raman spectra, two main vibrational lines appearing at 159 cm -1 and 188 cm -1 are characteristic for phonon vibrations of CdTe-like LO and CdSe-like LO modes as observed in [12,13]. When the fabricating temperature is as low as 180 o C, the intensity of the CdTe-like LO phonon is much higher compared to that of the CdSe-like LO phonon, proving that there are more formations of Cd-Te bonds than of Cd-Se in the alloy.…”