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Effect of X-ray irradiation on the blinking of single silicon nanocrystals
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0001-5304-913X
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0003-3833-9969
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
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2015 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 212, no 12Article in journal (Refereed) Published
Abstract [en]

Photoluminescence (PL) intermittency (blinking) observed for single silicon nanocrystals (Si-NCs) embedded in oxide is usually attributed to trapping/de-trapping of carriers in the vicinity of the NC. Following this model, we propose that blinking could be modified by introducing new trap sites, for example, via X-rays. In this work, we present a study of the effect of X-ray irradiation (up to 65 kGy in SiO) on the blinking of single Si-NCs embedded in oxide nanowalls. We show that the luminescence characteristics, such as spectrum and life-time, are unaffected by X-rays. However, substantial changes in ON-state PL intensity, switching frequency, and duty cycle emerge from the blinking traces, while the ON- and OFF- time distributions remain of mono-exponential character. Although we do not observe a clear monotonic dependence of the blinking parameters on the absorbed dose, our study suggests that, in the future, Si-NCs could be blinking-engineered via X-ray irradiation.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2015. Vol. 212, no 12
National Category
Other Physics Topics
URN: urn:nbn:se:kth:diva-174101DOI: 10.1002/pssa.201532652ISI: 000366589900006ScopusID: 2-s2.0-84949591107OAI: diva2:857823

QC 20151001

Available from: 2015-09-30 Created: 2015-09-30 Last updated: 2016-01-15Bibliographically 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.
, Trita-ICT, 2015:09
National Category
Physical Sciences
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)

QC 201501001

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

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