Structural, electronic and optical calculations of Cu(In,Ga)Se2 ternary chalcopyrites

In this work, we have investigated the structural, electronic and optical properties of the ternary I-III-VI2 chalcopyrite semiconductors ABX(2) (A = Cu, B = In, Ga, X = Se) by means of a first-principles density-functional total-energy calculation with the local-density approximation (LDA), using the all-electron full-potential linear-augmented plane-wave method (FP-LAPW). The equilibrium lattice constants and the bulk moduli (a, c, c/a, u and B-0) are compared with other theoretical calculations. The energy gap at ambient pressure is found to be direct and the nature of the gap crucially depends on the manner in which the d electrons of the A atoms are treated. We have also reported the optical properties of two chalcopyrite semiconductors CuInSe2 and CuGaSe2. Results on complex dielectric functions, refractive indices n, extinction coefficients k, and normal-incidence reflectivity R in the two crystals are given and compared with earlier data where available. We analyze in detail the structures of the dielectric function observed in the studied energy region. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.