| Autor: |
Wang, Feilong, Ou, Qiongrong, Zhang, Shuyu |
| Rok vydání: |
2022 |
| Předmět: |
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| Zdroj: |
Phys. Rev. B 106, 155425 (2022) |
| Druh dokumentu: |
Working Paper |
| DOI: |
10.1103/PhysRevB.106.155425 |
| Popis: |
Silicon photoluminescence and lasing have been critical issues to breakthrough bottlenecks in the understanding of luminescence mechanisms. Unfortunately, long-standing disputes about the exciton recombination mechanism and fluorescence lifetime remain unresolved, especially about whether silicon nanocrystals (Si NCs) can realize fast direct-bandgap-like optical transitions. Here, using ground-state and excited-state density functional theory (DFT), we obtained intrinsic phonon-free optical transitions at sizes from Si22 to Si705, showing that very small Si NCs can realize a strong direct optical transition. Orbital labeling results show that this rapid transition does not come from the {\Gamma}-{\Gamma} -like transition, contrary to the conclusions from the effective mass approximation (EMA) and that {\Gamma}-X mixing leads to a quasi-direct bandgap. This anomalous transition is particularly intense with decreasing size (or enhancement of quantum confinement). By investigating electron and hole distributions generated in the optical transition, localized state-induced enhanced emission (LIEE) in Si NCs was proposed. Quantum confinement (QC) distorts the excited-state electron spatial distribution by localizing Bloch waves into the NC core, resulting in increased hole and electron overlap, thus inducing a fast optical process. This work resolves important debates and proposes LIEE to explain the anomalous luminescence--a phase transition from weak (or none) luminescent state to strong optical transition, which will aid attempts at realizing high-radiative-rate NCs materials and application-level Si lasers. |
| Databáze: |
arXiv |
| Externí odkaz: |
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