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 (≲ 10 μ eV) 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.