Growth, structural characterization, and optical band gap of Cu(In1-xGax)5Se8 alloys

The phase diagram of the Cu(In1-xGax)(5)Se-8 (0 less than or equal to x less than or equal to 1) alloy system, prepared by direct fusion of the stoichiometric mixture of the elements, has been established by X-ray diffraction (XRD) and differential thermal analysis (DTA). The presence of a tetragonal structure at room temperature is found in the composition range 0.4 less than or equal to x less than or equal to 1.0. The reason for the reported tetragonal and hexagonal structures of CuIn5Se8 an also their co-existence below x < 0.4 observed in the present work is explained. In the composition range 0 less than or equal to x less than or equal to 1, the unit cell lattice parameters a and c of the tetragonal phase vary from 5.73-5.48 Angstrom and 10.90-11.56 Angstrom, respectively. From the absorption coefficient spectra, the band gap energy is found to vary from about 1.17 to 1.85 eV, with a downward bowing parameter b(2) approximate to 0.21 eV. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.