Fine structure of dark and bright excitons in vertical electric fields: Atomistic theory of alloyed self-assembled InGaAs quantum dots

Abstract

The vertical electric field response of dark- and bright-excitonic fine structures in self-assembled quantum dots remains largely unexplored. Using an atomistic tight-binding model, combined with a configuration-interaction approach, we show that the fine structure of both bright and dark excitons can be effectively tuned with a vertical field. The dark-exciton splitting reveals parabolic evolution under an applied electric field, contrary to linearlike trends for the bright-exciton splitting, with a linear change rate of the latter related to the bright-dark splitting. Atomistic results are further investigated in terms of the hole-band-mixing term, which reverses its sign under the electric field leading to a vanishing bright-exciton fine structure, and a minimum of the dark-exciton splitting in a nonalloyed case. Surprisingly, we find that the dark-exciton optical activity is also highly tunable with the electric field, despite the quantum dot's cylindrical shape, with potential implications for applications involving dark excitons. Finally, we study different random realizations of the same alloyed quantum dot, showing that mere alloy randomness substantially affects the bright-exciton splitting both at zero field and at the splitting minimum.