Electronic and optical features of the mixed crystals Ag0.5Pb1.75Ge(S1–xSex)4

Abstract

A single crystal with the Ag_0.5Pb_1.75GeS₃Se composition (25 mol% Ag_0.5Pb_1.75GeSe₄) was grown and characterized. Its phase diagram was explored. The section is non-quasi-binary. The role of defects in the conductivity mechanism was explored by electrical, optical and photoconductivity measurements. The band gap value was around 2.0 eV at 100 K. Two photoconductivity maxima with λ_m1 = 615 nm and λ_m2 = 775 nm were dominant at 100 K. We have performed X-ray crystallographic data analysis of Ag_0.5Pb_1.75GeS₃Se and the obtained data were used as the starting point for a comprehensive theoretical investigation of the electronic structure using the all-electron full potential linearized augmented plane wave method within density functional theory. The calculations have confirmed that the investigated compound possesses an indirect band gap of about 1.6 eV in good agreement with the experimental value. The angular momentum decomposition of the atoms projected density of states show there exists a strong hybridization between various states, and evaluated the origin of the chemical bonding.