Electronic and optical properties of Cu₂ZnGeX₄ (X = S, Se and Te) quaternary semiconductors

The electronic structures and optical properties of Cu ₂ZnGeS₄, Cu₂ZnGeSe₄ and Cu ₂ZnGeTe₄ in kesterite and stannite structures are investigated using first-principles calculations. The critical points in the optical spectra are assigned to the interband transitions according to the calculated band structures. The trends in the variation of the electronic and optical properties are discussed with respect to the crystal structure and the anion atomic number. Our calculated properties, such as, lattice constants, optical transitions, refractive index and dielectric constants are compared to the available experimental data and good agreement is obtained.