Temperature Dependent Excitonic Transition Energy and Enhanced Electron-Phonon Coupling in Layered Ternary SnS 2-x Se x Semiconductors with Fully Tunable Stoichiometry.

In this study, a series of SnS _2-x Se _x (0 ≤ x ≤ 2) layered semiconductors were grown by the chemical-vapor transport method. The crystal structural and material phase of SnS _2-x Se _x layered van der Waals crystals was characterized by X-ray diffraction measurements and Raman spectroscopy. The temperature dependence of the spectral features in the vicinity of the direct band edge excitonic transitions of the layered SnS _2-x Se _x compounds was measured in the temperature range of 20-300 K using the piezoreflectance (PzR) technique. The near band-edge excitonic transition energies of SnS _2-x Se _x were determined from a detailed line-shape fit of the PzR spectra. The PzR characterization has shown that the excitonic transitions were continuously tunable with the ratio of S and Se. The parameters that describe the temperature variation of the energies of the excitonic transitions are evaluated and discussed.