Electron–hole symmetry breakings in optical fine structures of single self-assembled quantum dots

The effects of electron–hole (e–h) symmetry breaking on the optical fine structure splitting (FSS) of single excitons in individual InGaAs/GaAs self-assembled quantum dots are experimentally and theoretically studied. The measured FSSs of small InGaAs/GaAs self-assembled quantum dots show a monotonic decrease with increasing emission energy and eventually almost vanish (View the MathML source) in the high energy regime. A theory based on 3D asymmetric parabolic model for e–h exchange interaction in combination with 3D finite difference simulations for Ga-diffused InGaAs/GaAs QDs is developed to explore the underlying physics. The reduced FSSs in the high emission energy regime are shown closely related to the e–h wave function symmetry breaking which is especially significant in highly Ga-diffused quantum dots. The Ga-diffusion induced e–h asymmetry reduces the e–h wave function overlap and results in the feature of reduced fine energy splitting.