The paper by Kawai et al. (pp. 29–37) aims to complete previous theoretical analysis on Ge-doped GaAs alloys, here mainly focusing on the impact that the formation of GaAs and Ge clusters, in conjunction with their morphology, has in the final bandgap of such systems. For investigating the relationship between the local geometry of the alloy vs. the bandgap opening, the authors analyze several representative extended alloy models with different local geometry and composition. The back cover shows the preferential formation of n- and p-type GaAs clusters in a Ge matrix (top panel) and their charge density (bottom panel). The atoms of the Ge matrix are depicted by green intermediate spheres, the Ga atoms by large pink and the As atoms by small purple ones. The agreement with the experimental trend shows the appropriateness of the modellization (inset plot).