Quantum-confined Stark shifts of charged exciton complexes in quantum dots

We probe the permanent excitonic dipole of neutral and positively charged excitons in individual In0.5Ga0.5As self-assembled quantum dots using Stark effect perturbation spectroscopy. A systematic reduction of the permanent excitonic dipole is found as excess holes are controllably added to individual dots containing a single exciton (X-0). Calculations of the few-body states show that this effect arises from a strong, Coulomb-mediated, spatial redistribution of the few-body wave function upon charging. By investigating correlations between the permanent dipole, polarizability, and the emission energy of X-0 for many dots, we also show that the strength of the In:Ga composition gradient is related to the absolute In content.