Optical phonons of SnSe(1-x)Sx layered semiconductor alloys

TL;DR

This study investigates how optical phonons in layered SnSe1-xSx alloys evolve with composition using polarized Raman spectroscopy, revealing polarization behaviors, crystallographic orientations, and phonon mode characteristics.

Contribution

It provides new insights into the polarization dependence and phonon mode behavior in SnSe1-xSx alloys across different compositions.

Findings

Ag2 mode's maximum intensity aligns with the armchair direction regardless of excitation wavelength.

Lower-frequency modes exhibit one-mode behavior, higher-frequency modes show two-mode behavior.

Polarization dependence varies with excitation wavelength for some Raman modes.

Abstract

The evolution of the optical phonons in layered semiconductor alloys SnSe1-xSx is studied as a function of the composition by using polarized Raman spectroscopy with six different excitation wavelengths (784.8, 632.8, 532, 514.5, 488, and 441.6 nm). The polarization dependences of the phonon modes are compared with transmission electron diffraction measurements to determine the crystallographic orientation of the samples. Some of the Raman modes show significant variation in their polarization behavior depending on the excitation wavelengths. It is established that the maximum intensity direction of the Ag2 mode of SnSe1-xSx (0<=x<=1) does not depend on the excitation wavelength and corresponds to the armchair direction. It is additionally found that the lower-frequency Raman modes of Ag1, Ag2 and B3g1 in the alloys show the typical one-mode behavior of optical phonons, whereas the higher-frequency modes of B3g2, Ag3 and Ag4 show two-mode behavior.