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Non-radiative decay in Si/SiO2 quantum dots in transition from dark to bright exciton states
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. (Nano Silicon group)ORCID iD: 0000-0003-3833-9969
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. (Nano Silicon group)ORCID iD: 0000-0003-2562-0540
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0002-5260-5322
(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-174096OAI: oai:DiVA.org:kth-174096DiVA: diva2:857796
Note

QS 2015

Available from: 2015-09-30 Created: 2015-09-30 Last updated: 2015-10-01Bibliographically approved
In thesis
1. Carrier Dynamics in Single Luminescent Silicon Quantum Dots
Open this publication in new window or tab >>Carrier Dynamics in Single Luminescent Silicon Quantum Dots
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bulk silicon as an indirect bandgap semiconductor is a poor light emitter. In contrast, silicon nanocrystals (Si NCs) exhibit strong emission even at room temperature, discovered initially at 1990 for porous silicon by Leigh Canham. This can be explained by the indirect to quasi-direct bandgap modification of nano-sized silicon according to the already well-established model of quantum confinement.

In the absence of deep understanding of numerous fundamental optical properties of Si NCs, it is essential to study their photoluminescence (PL) characteristics at the single-dot level. This thesis presents new experimental results on various photoluminescence mechanisms in single silicon quantum dots (Si QDs).

The visible and near infrared emission of Si NCs are believed to originate from the band-to-band recombination of quantum confined excitons. However, the mechanism of such process is not well understood yet. Through time-resolved PL decay spectroscopy of well-separated single Si QDs, we first quantitatively established that the PL decay character varies from dot-to-dot and the individual lifetime dispersion results in the stretched exponential decays of ensembles. We then explained the possible origin of such variations by studying radiative and non-radiative decay channels in single Si QDs. For this aim the temperature dependence of the PL decay were studied. We further demonstrated a model based on resonance tunneling of the excited carriers to adjacent trap sites in single Si QDs which explains the well-known thermal quenching effect.

Despite the long PL lifetime of Si NCs, which limits them for optoelectronics applications, they are ideal candidates for biomedical imaging, diagnostic purposes, and phosphorescence applications, due to the non-toxicity, biocompability and material abundance of silicon. Therefore, measuring quantum efficiency of Si NCs is of great importance, while a consistency in the reported values is still missing. By direct measurements of the optical absorption cross-section for single Si QDs, we estimated a more precise value of internal quantum efficiency (IQE) for single dots in the current study. Moreover, we verified IQE of ligand-passivated Si NCs to be close to 100%, due to the results obtained from spectrally-resolved PL decay studies. Thus, ligand-passivated silicon nanocrystals appear to differ substantially from oxide-encapsulated particles, where any value from 0 % to 100 % could be measured. Therefore, further investigation on passivation parameters is strongly suggested to optimize the efficiency of silicon nanocrystals systems.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xviii, 73 p.
Series
Trita-ICT, 2015:09
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-174149 (URN)978-91-7595-665-7 (ISBN)
Public defence
2015-10-23, SAL C, Electrum 229, KTH-ICT, Electrum 229, KTH-ICT, Kistagången 16, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 201501001

Available from: 2015-10-01 Created: 2015-10-01 Last updated: 2015-10-01Bibliographically approved

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Sangghaleh, FatemehSychugov, IlyaLinnros, Jan

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