Electron-Electron and Electron-Phonon Interactions in the Dynamics of Trap-Filling in Charged Quantum Dots

We analyze theoretically the effects of electron-electron and electron-phonon interactions in the dynamics of a system of a few electrons that can be trapped in a localized state and detrapped in an extended band state of a small quantum dot (QD) using a simple model. In our model, the QD is described by one or two single-particle energy levels, while the trap is described by one single-particle level connected to the QD by a hopping Hamiltonian. Electron-electron Coulomb repulsion and electron-phonon interactions are included in the localized trap state. In spite of its simplicity, the time-dependent model has no analytical solution, but a numerically exact one can be found at a relatively low computational cost. Using values of the parameters appropriate for defects in semiconductor QDs, we find that the electronic motion is quasi-periodic in time, with oscillations around mean values that are set in time scales of typically a few tenths of picoseconds. We increase the number of electrons initially in the QD from one to four and find that one electron is transferred to the trap state for three electrons in the QD. At the more efficient values of the electron-phonon coupling, these characteristics are quite independent of the value of the electron-electron Coulomb repulsion in the trap up to the value above which its infinite limit is reached. We conclude that strong electron-phonon interaction is an efficient mechanism that can provide the complete filling of a deep trap state on a sub- to picosecond time scale, faster than radiative exciton decay and Auger recombination processes. This leads to a complete suppression of the luminescence to the deep trap state and the accumulation of electrons in the QD.