Structural analysis and optical and electrical characterization of the ordered defect compound CuIn₅Se₈

Thin polycrystalline films of the ordered defect compound CuIn 5 Se 8 and CuInSe 2 are prepared on soda lime glass substrates at temperature 623 K by coevaporation of the constituent elements. X-ray diffraction, scanning electron microscopy and energy dispersive analysis of x-rays are done on the films for structural, morphological and composition determination. The lattice constants and the anion displacements for the compounds are calculated. The deformation parameter values show that the compounds have slightly distorted tetragonal unit cells. Assuming the atomic positions, the x-ray structure factor calculations have been made and the emergence of (110) reflection in the x-ray diffraction pattern of the ordered defect compound CuIn 5 Se 8 is explained. High resistivity measured for the compound film is attributed to the compensated defect levels in it. Hot probe measurements show the conductivity of the films to be n-type. A band gap E g = 1.32 eV is observed for the compound and the increase in band gap compared to E g = 0.98 eV for CuInSe 2 is explained as a consequence of the lowering of the valence band due to weaker SeΓ 15 (p)–CuΓ 15 (d) repulsion in the defect compound and electronic passivation due to 2V Cu –In Cu pairing.