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

Ingots of several compositions of the Cu(In1-xGa x)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 E G 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 deg. 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) A for x = 0, to 5.93231(8) and 11.825(4) A for x = 1. A phase transition to a cubic phase in the whole range of composition was observed above 620 deg. C. The energy band gap has been determined to be direct and varies linearly with composition x