Optical properties of Tl₂In₂Se₃S layered single crystals

Abstract

The optical properties of Tl2In2Se3S layered single crystals have been analyzed using transmission and reflection measurements in the wavelength region between 500 and 1100 nm. The optical indirect transitions with a band gap energy of 1.96 eV and direct transitions with a band gap energy of 2.16 eV were determined from analysis of absorption data at room temperature. Dispersion of the refractive index is discussed in terms of the Wemple-DiDomenico single-effective-oscillator model. The refractive index dispersion parameters - oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index - were found to be 4.67 eV, 45.35 eV, 1.38 x 1014 m-2 and 3.27, respectively. Transmission measurements were also performed in the temperature range 10-300 K. As a result of temperature-dependent transmission measurements, the rate of change in the indirect band gap with temperature, i.e. = -5.6 x 10-4 eV/K, and the absolute zero value of the band gap energy, Egi(0) = 2.09 eV, were obtained.