Ranges of solid solubility and optical energy gap values in CuIn(SxSeyTe1−xy)2 alloys

Abstract
Equilibrium conditions for the alloy system CuIn(SxSeyTe1−xy)2 were determined throughout the complete composition range. Polycrystalline samples of 60 different compositions were prepared by a melt and anneal technique, annealing times of up to three months at 600 °C being required. Debye–Scherrer x‐ray powder photographs were used to investigate the equilibrium conditions. Single phase behavior was found over approximately two‐thirds of the composition range, a broad miscibility gap being found on the CuIn(SxTe1−x)2 edge and extending into the center of the diagram. All phases were found to have the chalcopyrite structure with c/a=2. Values of a were determined in all cases and hence contours of constant a were plotted. Optical absorption measurements were carried out on all single phase samples to determine values of energy gap E0 at 70 and 300 K. For each temperature, the variation of E0 was fitted to a power series in x and z(=1−xy) and hence contours of constant E0 plotted. The experimental values were compared with the predictions of the interpolation equation of Williams et al. [J. Electronic Mater. 7, 639 (1978)].