Thermodynamic stability and gap modulation in defect and Zn-substituted CuAl2X4 (X = S, Se, and Te) chalcopyrite compounds

Abstract

In this study, we have examined the structural and electronic properties of defect and Zn-substituted CuAl${}_2$X${}_4$ (X $=$ S, Se, and Te) chalcopyrite type compounds using the density functional formalism within the pseudopotential framework, employing plane waves as the basis set. All calculations are carried out using the ab initio lattice parameters. The structural analysis indicates that CuAl${}_2$X${}_4$ (X $=$ S, Se, and Te) exhibits tetrahedral distortion due to the presence of vacancy sites. However, with the substitution of Zn atoms at the vacancy sites, the tetrahedra remain distorted. The values of lattice constants are more in the substituted compounds than that of the defect compounds. Both the defect and substituted compounds are thermodynamically stable, as evidenced by their negative cohesive energy values. The analysis of electronic behavior reveals that these compounds are conducting in nature, however, in the defect compounds, the Fermi level is close to the valence band, whereas, in the substituted compounds, the Fermi level lies in the conduction band region. The presence of Zn atoms reduces the electronic band gap than that of the defect compounds.