Absorption and Photoluminescence of Silicon Nanocrystals Investigated by Excited State DFT: Role of Embedding Dielectric and Defects

Absorption and photoluminescence (PL) properties of silicon (Si) nanocrystals (NCs) covered with dioxide ( SiO 2 ) are fairly well unraveled; corresponding information for nitride Si 3 N 4 coverage is scarce. We elucidate important optical electronic features depending on the embedding dielectric interface defect (dangling bond, DB) properties. Using density functional theory (DFT) time-dependent (TD-) DFT ground state (GS) excited (ES) properties, respectively, we compute fully NH - OH-covered NCs 11–26 Å size, enabling comparisons experimental data. Our non-radiative Shockley-Read-Hall (SRH) recombination model DBs at NC/dielectric interfaces demonstrates that SRH substantially higher -covered NCs. An ensemble TD-DFT calculation eight lowest fundamental transitions accurately describes absorption edge. Exciton binding energies significantly smaller in versus due to delocalizing self-localizing impact onto exciton. find rates -embedded However, renders PL inferior their counterparts. Finally, explain a discrepancy gaps free-standing oxidized by considering adequate phononic boundary conditions.