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

Electronic structural calculations of chalcopyrite-type CuInSe2 and its related compounds, CuGaSe2 and CuAlSe2, were performed by a recently proposed screened-exchange local density approximation (sX-LDA) method. The theoretical band gaps of CuInSe2, CuGaSe2, and CuAlSe2, 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 CuInSe2 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 CuInSe2 (0.96 eV), CuGaSe2 (1.36 eV), and CuAlSe2 (2.22 eV). The obtained electronic structures and band gap energies of CuInSe2, CuGaSe2, and CuAlSe2 are discussed on the basis of schematic molecular orbital diagrams of tetrahedral CuSe47-, InSe45-, GaSe45-, and AlSe45- clusters. (C) 2010 The Japan Society of Applied Physics