The evolution of the optical phonons in layered semiconductor alloys SnSe(1–x)Sx 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 SnSe(1−x)Sx (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.
Bibliographical noteFunding Information:
This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry and Energy (MOTIE) of the Republic of Korea (No. 20173010012980) and the Basic Science Research Program through the National Research Foundation of Korea (NRF-2017R1A5A1014862, NRF-2019R1F1A1058473 and NRF-2019R1A6A1A11053838) and Institute for Basic Science (IBS-R026-D1). T.S. acknowledges the supports from Swedish International Development Cooperation Agency (SIDA) through Sweden and Royal University of Phnom Penh (RUPP)’s Pilot Research Cooperation Programme (Sida Contribution No. 11599) and RUPP.
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