Ab initio modeling of phonon-assisted relaxation of electrons and excitons in semiconductor nanocrystals for multiexciton generation

The electron-phonon interaction is fundamental to many physical and chemical processes. The ab initio computation based on modern many-body Green's function (MBGF) theory can be used to accurately calculate the properties of matters including the electron-nucleus coupling of bulk materials and nanocrystals. Yet it is hard to find reports of computed electron-phonon interaction and phonon-assisted dynamics of electrons and excitons in nanocrystals using MBGF theory without any input of semiempirical parameters. We establish a computationally executable approach for modeling electron-phonon and exciton-phonon interaction under the framework of the GW Bethe-Salpeter equation in semiconductor nanoclusters. We computed both nonradiative relaxation and inelastic scattering of electrons and excitons, and uncovered that both single-phonon relaxation and multiple-phonon relaxation are significant for nonradiative relaxation of electrons and excitons in nanocrystal of Si-46, and the two relaxations correspond to two types of physical processes that have totally different spectral line shapes, respectively. The inelastic scattering decay is a primary decay mechanism for multiexciton relaxation. The computed single-phonon and multiphonon nonradiative relaxation rates in Si(46 )are between 1 and 1000 fs for different excitonic energies, which is consistent with experimental results reported for similar nanocrystals.

Automated summary

The study establishes a computationally executable approach for modeling electron-phonon and exciton-phonon interaction in semiconductor nanoclusters. It reveals the significance of single-phonon and multiple-phonon nonradiative relaxation for electrons and excitons in nanocrystals. Nonradiative relaxation rates in Si(46) are consistent with experimental results reported for similar nanocrystals.