Phonon Bottleneck in the Hot Electron Relaxation of n-Doped Quantum Dots: A Large-Scale Nonadiabatic Dynamics...

It is still controversial whether the phonon bottleneck effect, traditionally considered to be negligible in strongly confined quantum dots (QDs) due to the efficient electron-hole energy exchange in Auger processes, could become more significant in n-doped QDs with fully occupied valence bands. In this study, we employ a generalized Holstein-Peierls Hamiltonian to describe the electron-vibration couplings in QDs and study the hot electron relaxation dynamics by large-scale nonadiabatic dynamics simulations based on the proposed effective Hamiltonian method. The high-energy electron undergoes rapid relaxation, driven by the high electronic density of states (DOS) and strong effective electron-vibration coupling in the energy space. In contrast, the time propagation of medium- and low-energy electrons shows an evident phonon bottleneck effect, characterized by the large energy separations that necessitate multiphonon processes, resulting in the relaxation time on the nanosecond scale. The electron relaxation rate is found to exhibit a power-law dependence on the electronic DOS, with an exponent of approximately 1.62. We also identify the key role of the quantum decoherence effect, which suppresses unphysical overcoherent electron propagation and enables exponential population decay to the conduction band minimum. The electron relaxation time calculated by the real-time simulations further validates the theoretical prediction by the obtained power-law formula. These theoretical findings elucidate the intricate interplay of electronic transitions, electron-vibration couplings, and quantum decoherence in QDs, providing insights for further optimization of QD-based optoelectronic devices.