Indirect Energy Gap in GaSe and GaS

Abstract

Abstract Optical absorption measurements on thick monocrystalline samples of GaSe 1− x S x show that in these mixed crystals the lowest energy gap is indirect in the complete range 0 ≦ x ≦ 1. These results are contrary to earlier reports which indicate that GaSe is a direct gap semiconductor. In the case of GaS the absorption spectra allow a tentative identification of the phonons involved in the indirect transition.