Electronic and optical properties of Tl4GeX3 (X = S, Se and Te) compounds for optoelectronics applications: insights from DFT-computations

In this work, first-principles computational study on the structural, electronic and optical properties of Tl4GeS3, Tl4GeSe3 and Tl4GeTe3 ternary compounds are presented. The computations are performed with pseudopotential plane wave method based on density functional theory with the generalized gradient approximation of Perdew–Burke and Enzerhof (PBE-GGA). The calculated structural, electronic and optical parameters are consistent with the available experimental results. The computed electronic band structures confirm the semiconducting nature for these compounds with direct band gaps of 0.17 eV, 0.085 eV and 0.015 eV for Tl4GeS3, Tl4GeSe3 and Tl4GeTe3, respectively. Furthermore, the electron charge density distribution indicated that the nature of bonds between Ge and S/Se/Te are covalent nature, whereas Ge and S/Se/Te anions formed ionic bonds. The optical parameters revealed that Tl4GeS3, Tl4GeSe3 and Tl4GeTe3 are highly dielectric materials and has the potential to be beneficial in the optoelectronic device applications.