Effects of atomic clustering on the optical properties of III-V alloys
  Self-consistent electronic structure calculations together with a structural model are used to study the effect of short-range atomic order on the optical properties of otherwise random Al(0.5)Ga(0.5)As, Ga(0.5)In(0.5)P, and Al(0.5)In(0.5)As alloys. We find that clustering can reduce the direct band gap of these alloys by as much as 100 meV. Furthermore, sufficiently strong clustering is predicted to transform Al(0.5)Ga(0.5)As into a direct gap material. 
Kurt A. Mader and Alex Zunger