First Principles study of Silver Argyrodites-structured compounds A8BC6 (A=Ag; B=Si, Ge; C=Te) for Opto-electronic application

Abstract

The structural and optical properties of a material are studied using Density Functional Theory. By the method of full potential linearized augmented plane wave (FP-LAPW) silver argyrodites Ag8SiTe6 and Ag8GeTe6 has been investigated. To obtain stable geometry of A8BC6 materials, the energy minimization approach is applied. The Generalized Gradient Approximation (GGA) approach is used to optimize the crystal structure of the Argyrodites materials. All these compounds crystalize in a cubic unit cell with lattice constant increasing from 12.13 Å (Si) to 12.28 Å (Ge). The mBJ-functional shows a semiconducting nature Ag8SiTe6 for and metallic nature for Ag8GeTe6 of these compounds with an indirect band gap lying at the L-X symmetry points with a band gap of 0.24 eV (Si) and 0.0068 eV (Ge) to obtain the optical properties such as refractive index, complex dielectric constant with real and imaginary part of dielectric function, and other optical properties are discussed. Effective mass of electrons is smaller than those of holes resulting in higher carrier mobility for electrons. Due their direct band gap, these Argyrodites materials could be particularly useful in optoelectronic devices.