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We use an $sp^3d^5s^* $ tight-binding model to investigate the electronic andoptical properties of realistic site-controlled (111)-oriented InGaAs/GaAsquantum dots. Special attention is paid to the impact of random alloyfluctuations on key factors that determine the fine-structure splitting inthese systems. Using a pure InAs/GaAs quantum dot as a reference system, weshow that the combination of spin-orbit coupling and biaxial strain effects canlead to sizeable spin-splitting effects in these systems. Then, a realisticalloyed InGaAs/GaAs quantum dot with 25\% InAs content is studied. Our analysisreveals that the impact of random alloy fluctuations on the electronic andoptical properties of (111)-oriented InGaAs/GaAs quantum dots reduces stronglyas the lateral size of the dot increases and approaches realistic sizes. Forinstance the optical matrix element shows an almost vanishing anisotropy in the(111)-growth plane. Furthermore, conduction and valence band mixing effects inthe system under consideration are strongly reduced compared to standard(100)-oriented InGaAs/GaAs systems. All these factors strongly indicate areduced fine structure splitting in site-controlled (111)-oriented InGaAs/GaAsquantum dots. Thus, we conclude that quantum dots with realistic (50-80~nm)base length represent promising candidates for polarization entangled photongeneration, consistent with recent experimental data.

physical review. b./physical review. b

Theoretical analysis of influence of random alloy fluctuations on the  opto-electronic properties of site-controlled (111)-oriented InGaAs/GaAs  quantum dots