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Impact of short-range order and clusterization on the bandgap bowing: First-principles calculations on the electronic properties of metastable (GaAs)1–x(Ge2)x alloys



The large, negative, and asymmetric bandgap bowing in (GaAs)1–x(Ge2)x alloys is investigated as function of Ge concentration, via the combination of density functional theory and GW0 approach. We revealed that the large negative character of the gap bowing is due to the increase of the octet-rule violating bonds (bad bonds) as Ge reaches intermediate concentrations, while the asymmetry is governed by the presence of GaAs clusters embedded in the Ge matrix at Ge concentration between 0.3 and 1. Both the clusterization and fragmentation of GaAs region are phenomena able to delocalize the extracharges on the formed bad bonds, causing thermodynamic stabilization, and bandgap increase. Our results are in very good agreement with the experimental ones, confirming the bandgap bowing dependency on the nearest-neighbor atomic interactions.