Evidence for a modified-stannite crystal structure in wide band gap Cu-poor CuIn1-xGaxSe2:: Impact on the optical properties

The crystal structure of high Ga-content CuIn1-xGaxSe2 (CIGSe) compounds has been further investigated with the help of single crystal x-ray diffraction technique. It is known that CIGSe compounds adopt the chalcopyrite crystal structure. In the case of Cu-poor, Ga-rich CIGSe, the present study shows that an alternative structure should be considered. This structure is derived from that of stannite in which there is a Ga/In segregation on two different atomic planes. The diffuse reflectance measurements of the Cu-poor compound reveal a slightly different band gap and a smoother transition compared with those of the stoichiometric compound. (C) 2008 American Institute of Physics.