Vibrational modes in (TlGaS₂)_x‒(TlGaSe₂)_1−x mixed crystals by Raman measurements: compositional dependence of the mode frequencies and line-shapes

TlGaS₂ and TlGaSe₂ ternary semiconducting compounds have been of scientific interest due to their large ultrafast optical nonlinearity characteristics. These remarkable properties make them promising semiconducting materials in photonic applications. A series of (TlGaS₂)_x‒(TlGaSe₂)_1−x layered mixed crystals grown by Bridgman method were investigated from the standpoint of their Raman spectroscopy characteristics. Experimental Raman scattering study of crystals were reported in the frequency range of 80–400 cm⁻¹ for compositions of x = 0, 0.25, 0.50, 0.75 and 1.0. The effects of crystal disorder on the line-width broadening of Raman-active modes were studied in detail. The asymmetry in the Raman line-shape was analyzed for two highest-frequency intralayer mode presenting two-mode behavior. It was shown that mixed crystal disorder effect is the major source for change of Raman line-shape with composition.