Optical phonons of SnSe((1−x))S(x) layered semiconductor alloys

The evolution of the optical phonons in layered semiconductor alloys SnSe((1–x))S(x) 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 A(g)(2) mode of SnSe((1−x))S(x) (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 A(g)(1), A(g)(2) and B(3g)(1) in the alloys show the typical one-mode behavior of optical phonons, whereas the higher-frequency modes of B(3g)(2), A(g)(3) and A(g)(4) show two-mode behavior.