Tunable valleytronics with symmetry-retaining high polarization degree in SnSxSe1−x model system

Abstract

SnS has recently been shown to possess unique valleytronic capability with large polarization degree, where non-degenerate valleys can be accessed using linearly polarized light, bestowed upon by the unique anisotropy and wavefunction symmetry. It is thus of utmost importance to demonstrate the extension of such effects for the IV-VI system in general, thereby elucidating the generality and tunability of such valleytronics. We show the highly tunable valleytronics via gradual compositional control of the Tin(II) Sulfo-Selenide (SnSxSe1-x) alloy system with excellent retainment of symmetry-determined selection rules. We show the presence of both ΓY and ΓX valleys in all alloy compositions via selectivity in absorption and emission of linearly polarized light by optical reflection (R)/transmission (T) and photoluminescence (PL) measurements, and tuned the bandgaps of the valleys within a range of 1.28eV to 1.05eV and 1.48eV to 1.24eV respectively. This simultaneous tuning of non-degenerate valleys agrees well with theoretical calculations. We then fitted the bandgap values in compositional space, obtaining the bowing parameters as a useful database. We further demonstrated the feasibility of using IV-VI valleytronics systems in general by elucidating the retainment of strong polarization degrees of as high as 91% across all compositions. The generalization of such purely symmetry-dependent valleytronics also opens up opportunities for discovery of more multi-functional materials.

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

“…Obviously, Raman peaks are broadened in the alloy case because of the crystal disorder and mass change in layer with compositional fluctuation. , Reasonably, SnSe-like Raman peaks at 111 cm –1 (B 3g ), 133 cm –1 (A g ), and 156 cm –1 (A g ) are slightly blue-shifted compared with reported SnSe Raman peaks (109 and 150 cm –1 ) . This alloy behavior can also be explained by the modified random element isodisplacement model . Meanwhile, SnS-like Raman peaks at 178 cm –1 (B 3g ) and 197 cm –1 (A g ) are strongly blue-shifted toward reported SnS peaks (163 and 191 cm –1 ) .…”

“…The triangle and hexagon are experimental data, which are nonlinear-fitted and consistent with eqs , , and . Uniquely, I (A g ,∥) shows a period of 180° and reaches its maximum at θ = 130°, which indicates the AC (the strongest intensity) and ZZ (the weakest intensity) directions of SnS 0.5 Se 0.5 . , By contrast, I (B 3g ,∥) reaches its maximum at θ = 80° under a parallel configuration. For contrast, I (B 3g ,⊥) is suppressed at the cross polarization.…”

“…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. , …”

“…As is known, SnS and SnSe with an orthorhombic α-phase structure can be demonstrated as a highly distorted NaCl structure. The long pair electrons of Sn (5s) arranged in a distorted octahedron leads to the strong interlayer interaction . Thus, the PVD growth of SnS 0.5 Se 0.5 probably possesses a high growth rate along the vertical direction.…”

“…The corresponding SEM–EDS analysis can also be seen in Figures S7–S9. The averaged S/Se ratio is about 0.87 (design ratio = 1) because of the lower equilibrium pressure of the SnSe component as compared with SnS . It is believed that the improved LPPVD method can be helpful to the other ultrathin 2D anisotropic material growth.…”