Ordering-induced changes in the optical spectra of semiconductor alloys

It is shown how the recently predicted and subsequently observed spontaneous long-range ordering of pseudobinary A0.5B0.5C isovalent semiconductor alloys into the (AC)1(BC)1 superlattice structure (a CuAuI-type crystal) gives rise to characteristic changes in the optical and photoemission spectra. We predict new direct transitions and substantial splittings of transitions absent in the disordered alloy.