Optical Properties of CuGaS₂ near the Fundamental Absorption Edge

The absorption and reflection spectra of “green” and “orange” CuGaS 2 crystals, prepared by chemical transport reaction, have been studied at low temperatures. The “orange” crystal presents an excitonic spectrum characteristic for intrinsic material. The triplet structure can be explained by comparison with CuCl. This configuration involves that the upper valence band, as in the case of cuprous halides, is formed by a mixing of p‐ and d‐like wave functions. The observation of a n ‐ S h e by a wavelength modulation technique permits the calculation of the binding energy of the free exciton. The spectrum of the “green” sample, shifted towards the low‐energy side, is much more complicated. It is characteristic for a compound strongly perturbated by defects.