Absorption edge and optical constants of layered structured Tl₂Ga₂Se₃S single crystals

Abstract

The optical properties of Tl2Ga2Se3S layered crystals have been studied through transmission and reflection measurements in the photon energy range 1.13-2.82 eV. The optical indirect and direct transitions with band gap energies of 2.15 and 2.54 eV, respectively, were determined from the analysis of absorption data at room temperature. The dispersion of refractive index is discussed in terms of the Wemple-DiDomenico single-effective oscillator model. The refractive index dispersion parameters, namely oscillator and dispersion energies, oscillator strength and zero-frequency refractive index, were found to be 4.90 eV, 32.44 eV, 1.03x10(14) m(-2) and 2.76, respectively. Furthermore, the transmission measurements were made in the temperature range 10-300 K. As a result, the rate of indirect band gap variation with temperature gamma = -4.6x10(-4) eVK(-1) and the absolute zero value of the band gap energy E-gi(0) = 2.24 eV were obtained.