Effects of Ga addition to CuInSe2 on its electronic, structural, and defect properties

Using a first-principles band structure method we have theoretically studied the effects of Ga additions on the electronic and structural properties of ${\mathrm{CuInSe}}_{\mathrm{2}}.$ We find that (i) with increasing $x_{\mathrm{Ga}},$ the valence band maximum of ${\mathrm{CuIn}}_{\text{1−x}}{\mathrm{Ga}}_x{\mathrm{Se}}_{\mathrm{2}}$ (CIGS) decreases slightly, while the conduction band minimum (and the band gap) of CIGS increases significantly, (ii) the acceptor formation energies are similar in both ${\mathrm{CuInSe}}_{\mathrm{2}}$ (CIS) and ${\mathrm{CuGaSe}}_{\mathrm{2}}$ (CGS), but the donor formation energy is larger in CGS than in CIS, (iii) the acceptor transition levels are shallower in CGS than in CIS, but the ${\mathrm{Ga}}_{\mathrm{Cu}}$ donor level in CGS is much deeper than the ${\mathrm{In}}_{\mathrm{Cu}}$ donor level in CIS, and (iv) the stability domain of the chalcopyrite phase increases with respect to ordered defect compounds. Our results are compared with available experimental observations.