First-Principles Investigation of Structural, Electronic, and Elastic Properties of Cu(In,Ga)Se2 Chalcopyrite Alloys Using GGA+U

This paper presents a theoretical study of the structural, electronic, and elastic properties of gallium-doped CuInSe2 using the GGA exchange-correlation functional with the Hubbard correction for five Ga compositions: 0, 0.25, 0.5, 0.75, and 1. The found lattice parameters decrease with gallium composition and obey Vegard’s law. Traditional DFT calculations fail to explain the band structure of Copper Indium Gallium Selenide compounds (CIGS). The use of Hubbard corrections of d-electrons of copper, indium, gallium, and p-electrons of selenium opens the gap, showing a semiconductor’s behavior of CuInGaSe2 alloys in the range 1.04 eV to 1.88 eV, which are in good agreement with available experimental data and current theory using an expensive hybrid exchange-correlation functional. The obtained formation energies for the different gallium compositions are close to −1 eV/atom, and the phonon spectra indicate the thermodynamic stability of these alloys. The values of the elastic constant satisfy the Born elastic stability conditions, suggesting that these compounds are mechanically stable. Moreover, we compute the bulk modulus (B), shear modulus (G), Young’s modulus (E), Poisson ratio (p), Pugh’s ratio (r), and average Debye speed (v), and the Debye temperature (ΘD) with the Ga composition. There is a symmetry between our results and the experimental data, as well as earlier simulation results.