Coulomb interactions in single charged self-assembled quantum dots: Radiative lifetime and recombination energy

Abstract

We present results on the charge dependence of the radiative recombination lifetime, $\ensuremath{\tau}$, and the emission energy of excitons confined to single self-assembled InGaAs quantum dots. There are significant dot-to-dot fluctuations in the lifetimes for a particular emission energy. To reach general conclusions, we present the statistical behavior by analyzing data recorded on a large number of individual quantum dots. Exciton charge is controlled with extremely high fidelity through an $n$-type field effect structure, which provides access to the neutral exciton (${X}^{0}$), the biexciton $(2{X}^{0})$, and the positively $({X}^{1+})$ and negatively $({X}^{1\ensuremath{-}})$ charged excitons. We find significant differences in the recombination lifetime of each exciton such that, on average, $\ensuremath{\tau}({X}^{1\ensuremath{-}})/\ensuremath{\tau}({X}^{0})=1.25$, $\ensuremath{\tau}({X}^{1+})/\ensuremath{\tau}({X}^{0})=1.58$, and $\ensuremath{\tau}(2{X}^{0})/\ensuremath{\tau}({X}^{0})=0.65$. We attribute the change in lifetime to significant changes in the single particle hole wave function on charging the dot, an effect more pronounced on charging ${X}^{0}$ with a single hole than with a single electron. We verify this interpretation by recasting the experimental data on exciton energies in terms of Coulomb energies. We directly show that the electron-hole Coulomb energy is charge dependent, reducing in value by 5%--10% in the presence of an additional electron, and that the electron-electron and hole-hole Coulomb energies are almost equal.