On the band gap in (In2S3)x(CuIn5S8)1 − x alloy single crystals

For In2S3, CuIn5S8 and (In2S3)x(CuIn5S8)1 − x alloy single crystals grown by the Bridgman method (vertical variant), the transmittance spectra in the region of the fundamental absorption-band edge are studied at 80 and 295 K. From the spectra, the band gaps of the In2S3 and CuIn5S8 compounds and the alloys based on them are determined, and the dependences of the band gap on the composition parameter x of the alloys are established. It is shown that, at 80 and 295 K, the band gap nonlinearly varies with x and the variation is described by a quadratic function.