Ab Initio Modeling of Phonon-Assisted Relaxation of Electrons and Excitons in Semiconductor Nanocrystals for Multiexciton Generation

TL;DR

This paper models phonon-assisted relaxation processes of electrons and excitons in semiconductor nanocrystals using a GW-BSE framework, revealing significant multi-phonon effects and their impact on multiexciton relaxation mechanisms.

Contribution

It introduces a novel two-particle phonon modeling approach within GW-BSE to analyze nonradiative relaxation in nanocrystals, highlighting the importance of multi-phonon processes.

Findings

Multi-phonon relaxation rates are comparable to single-phonon rates.

Inelastic scattering is a primary decay mechanism for multiexciton relaxation.

Nonradiative relaxation rates exceed inelastic scattering rates for most excitonic states.

Abstract

Electron-phonon and exciton-phonon interactions in nanoclusters are formulated and computed under the framework of GW-BSE (Bethe-Salpeter equation) approach. The phonon effect is modeled with the two-particle representation for the first time. The nonradiative relaxation rates of electrons and excitons are calculated. It is uncovered that both single-phonon relaxation and multiple-phonon relaxation are significant in nanocrystals, and correspond to two types of physical processes that have totally different spectral lineshapes. Furthermore, the multiple-phonon relaxation always occurs and its rates are comparable to the corresponding single-phonon relaxation rates for both electrons and excitons in the system studied (Si46). The inelastic scattering rates of electrons and excitons are also calculated based on many-body Green function theory. For the electronic states in Si46, the inelastic scattering decay is predicted to be a primary decay mechanism for multiexciton relaxation, and nonradiative relaxation rates are larger than inelastic scattering rates for most excitonic states in Si46.