Electronic Structure and Characteristics of Chemical Bonds in CuInSe2, CuGaSe2, and CuAlSe2

Electronic structural calculations of chalcopyrite-type CuInSe 2 and its related compounds, CuGaSe 2 and CuAlSe 2 , were performed by a recently proposed screened-exchange local density approximation (sX-LDA) method. The theoretical band gaps of CuInSe 2 , CuGaSe 2 , and CuAlSe 2 , obtained by the conventional calculation method using a generalized gradient approximation (GGA) functional, were 0.04, 0.14, and 1.11 eV, respectively. These values were considerably underestimated in comparison with their experimental values of 1.04, 1.68, and 2.67 eV because the exchange–correlation energy was not precisely calculated. Therefore, electronic structural calculations of chalcopyrite-type CuInSe 2 and related compounds were performed with an sX-LDA functional to obtain accurate electronic structure. The present sX-LDA calculation successfully reproduced the band gaps of CuInSe 2 (0.96 eV), CuGaSe 2 (1.36 eV), and CuAlSe 2 (2.22 eV). The obtained electronic structures and band gap energies of CuInSe 2 , CuGaSe 2 , and CuAlSe 2 are discussed on the basis of schematic molecular orbital diagrams of tetrahedral CuSe 4 7- , InSe 4 5- , GaSe 4 5- , and AlSe 4 5- clusters.