COMPOSITION EFFECTS ON THE CRYSTAL-STRUCTURE OF CUINSE2

By x-ray powder diffraction and the Rietveld refinement method, the at omic positions in CuInSe2 were determined for compositions close to st oichiometry. The Se position, x(Se) was found to be correlated to the Cu content. According to a model proposed by Jaffe and Zunger [Phys. R ev, B 29, 1882 (1984)], changes in x(Se) induce a variation in the opt ical band gap, E(g). This could explain the spread in energy gap, E(g) , found by many authors for this compound. The increase in the lattice parameter, a, correlated with the difference between the energy dispe rsive analysis of x rays and x-ray diffraction determined Cu contents, suggests the presence of a fraction of Cu atoms as interstitials. (C) 1996 American Institute of Physics.