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

Abstract

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 Ag 2 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 Ag 1 , Ag 2 and B3g 1 in the alloys show the typical one-mode behavior of optical phonons, whereas the higher-frequency modes of B3g 2 , Ag 3 and Ag 4 show two-mode behavior.

Anisotropic Optical and Vibrational Properties of GeS

“…Due to the observed behavior of different peaks, we can assume that (i) the polarization properties of the B 2 1g mode can be used to determine the crystallographic axes in GeS, but without attribution the zigzag and armchair directions; (ii) the variation of the polarization axis of the A 3 g as a function of the excitation energy suggests that the electron-phonon coupling may change the A 3 g polarization axis (see the work in [32] for details); and (iii) due to 2-fold symmetries of the polarization properties (except for 1.96 eV) and the almost fixed polarization axis of the A 4 g mode, its polarization properties are good to identify the zigzag and armchair crystallographic directions. Note that the observed influence of the excitation energies on the axes and shape of polarization properties of phonon modes is very similar to those reported for different anisotropic layered materials, e.g., BP, ReS 2 , ReSe 2 , SnSe 1−x S x [6,9,[32][33][34]. Moreover, as the effect of thickness on the polarization properties of different modes in BP has been reported [6,33], the outline of further research on thin layers of GeS seems to be clear.…”

Circular SnS0.5Se0.5 Nanosheets with Highly Anisotropic Performance for Nanoelectronics

“…Wen et al found the highest anisotropic mobility ratio of 5.6 for ReS 1.02 Se 0.98 , which is larger than that of ReS 2 and ReSe 2 . As for 2D SnS 1– x Se x , the synthesis, valleytronics, optoelectricity, and anisotropic optical and structural characteristics as a function of content are systematically studied in recent years by us , and other groups. − It is confirmed that the polarized Raman spectrum and electrical and photoresponse time in the broadband spectrum are maintained and improved through alloying. However, in-plane anisotropic electrical and photoresponse properties of ultrathin 2D SnS 1– x Se x have rarely been reported, which also need an ultrathin rounded shape to stimulate the optimum anisotropic properties such as black phosphorus (BP), GaTe, and so on. , …”

“…The ultrathin orthorhombic SnS 0.5 Se 0.5 belongs to the D 2 h point group. Meanwhile, only A g and B 3g Raman modes can be found in the sample on the Y – Z plane (100), and their Raman tensors are given as follows ,, …”

“…The Raman scatter intensity I for Raman modes can be expressed as follows ,, Here, θ is the rotation angle and φ is the angle between the Z -axis and the 0° reference. According to the equations, B 2 implies the maximum of I (A g ,∥) when the incident light is parallel to the AC direction, while C 2 is the minimum value of this condition.…”

Anisotropic Optical And Vibrational Properties Of GeS

“…BP, ReS 2 , ReSe 2 , SnSe 1−x S x . [28][29][30][31][32] Moreover, as the effect of thickness on the polarization properties of different modes in BP has been reported, 29,30 the outline of further research on thin layers of GeS seems to be clear.…”