X-ray powder diffraction, phase transitions and optical characterization of the Cu(In1−xGax)3Te5 semiconducting system

Ingots of several compositions of the Cu(In1−xGax)3Te5 semiconducting system were prepared by the Vertical Bridgman technique. X-ray powder diffraction, differential thermal analysis and optical absorption studies were used to characterize the fundamental structural aspects and phase transitions and determine the energy band gap EG of this alloy system. It is found that a solid solution with a tetragonal chalcopyrite-related structure is formed over the entire range of composition for temperatures below 620 °C. The parameters a and c at room temperature of the tetragonal unit cell were found to vary linearly with composition x from 6.1639(4) and 12.346(6) Å for x = 0, to 5.93231(8) and 11.825(4) Å for x = 1. A phase transition to a cubic phase in the whole range of composition was observed above 620 °C. The energy band gap has been determined to be direct and varies linearly with composition x.