Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Biexciton Emission as a Probe of Auger Recombination in Individual 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, Material Physics, MF.ORCID iD: 0000-0003-2562-0540
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.
Show others and affiliations
2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 13, p. 7499-7505Article in journal (Refereed) Published
Abstract [en]

Biexciton emission from individual silicon nanocrystals was detected at room temperature by time-resolved, single-particle luminescence measurements. The efficiency of this process, however, was found to be very low, about 10-20 times less than the single exciton emission efficiency. It decreases even further at low temperature, explaining the lack of biexciton emission line observations in silicon nanocrystal single-dot spectroscopy under high excitation. The poor efficiency of the biexciton emission is attributed to the dominant nonradiative Auger process. Corresponding measured biexciton decay times then represent Auger lifetimes, and the values obtained here, from tens to hundreds of nanoseconds, reveal strong dot-to-dot variations, while the range compares well with recent calculations taking into account the resonant nature of the Auger process in semiconductor nanocrystals.

Place, publisher, year, edition, pages
2015. Vol. 119, no 13, p. 7499-7505
Keywords [en]
Augers, Efficiency, Optical waveguides, Silicon, Temperature, Auger recombination, Biexciton emission, Luminescence measurements, Poor efficiencies, Room temperature, Semiconductor nanocrystals, Silicon nanocrystals, Single dot spectroscopy
National Category
Other Chemistry Topics
Identifiers
URN: urn:nbn:se:kth:diva-166326DOI: 10.1021/acs.jpcc.5b01114ISI: 000352329500060Scopus ID: 2-s2.0-84926436244OAI: oai:DiVA.org:kth-166326DiVA, id: diva2:810847
Funder
Swedish Research CouncilCarl Tryggers foundation
Note

QC 20150508

Available from: 2015-05-08 Created: 2015-05-07 Last updated: 2018-11-13Bibliographically 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. p. xviii, 73
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
2. Optical Properties of Single Silicon Quantum Dots
Open this publication in new window or tab >>Optical Properties of Single Silicon Quantum Dots
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For over 60 years silicon (Si) has dominated the semiconductor microelectronics industry mainly due to its abundance and good electrical and material properties. The advanced processing technology of Si has made it the workhorse for photovoltaics industry as well. However, this material has also a big drawback: it is an indirect-bandgap semiconductor in its bulk form, hence an inefficient light emitter. This has hindered the silicon photonics revolution envisioned in 1980s, where photons were thought to replace electrons inside computer chips.

In parallel with the exponential scaling of Si transistor's size over the years, the discovery of quantum phenomena at the nanoscale raised new hopes for this semiconductor. In the 1990s bright luminescence from nanostructured porous Si was demonstrated claiming the quantum confinement effect as origin of the emission. Since then, an intense research activity has been focused on Si quantum dots (Si-QDs) due to their potential use as abundant and non-toxic light emitters. More precisely, they could be used as fluorescent biolabels in biomedicine, as light-emitting phosphors in e.g. TV screens or as down-converters in luminescent solar concentrators. Nevertheless, in order to realize such applications, it is necessary not only to improve the fabrication of Si-QDs but also to gain a better understanding of their photo-physics. Among different types of optical measurements, those performed at the single-dot level are free of sample inhomogeneities, hence more accurate for a correct physical description.

This doctoral thesis presents a study of the optical properties of single Si-QDs of different type: encapsulated in an oxide matrix, capped with ligands or covered by a thin passivation layer. The homogeneous photoluminescence (PL) linewidth is found to strongly depend on the type of embedding matrix, being narrower for less rigid ones. A record resolution-limited linewidth of ~200 μeV is measured at low temperatures whereas room-temperature values can even compete with direct-bandgap QDs like CdSe. Such narrow PL lines exhibit intensity saturation at high excitation fluxes without any indication of emission from multiexciton states, suggesting the presence of fast non-radiative Auger recombination. Characteristic Auger-related lifetimes extracted from power-dependent decays show a variation from dot-to-dot and confirm the low biexciton quantum efficiency.

For the first time, the absorption curve of single Si-QDs is probed by means of photoluminescence excitation in the range 2.0-3.5 eV. A step-like structure is found which depends on the nanocrystal shape considered and agrees well with simulations of the exciton level structure. Rod-like Si-QDs can exhibit ~50 times higher absorption than spherical-like ones due to local field effects and enhanced optical transitions. In contrast with previous studies, evidence of a direct-bandgap red-shift for small Si-QDs is missing at the single dot level, in agreement with atomistic calculations.

Low-temperature PL decay measurements reveal no triplet-like emission lines, but two ~μs decay constants appearing at low temperatures. They suggest presence of a temperature-dependent fast blinking process based on trapping/detrapping of carriers in the oxide matrix, leading to delayed emission. The proposed model allows to extract characteristic trapping/de-trapping rates for Si-QDs featuring mono-exponential blinking statistics. From PL saturation curves, ligand-passivated Si-QDs do not exhibit such detrimental phenomenon, in agreement with the proposed model.

Last, Si-QDs demonstrate to be very hard against ~10 keV X-ray radiation, in contrast with CdSe-QDs whose PL quenching is correlated with a change in the blinking parameters. This property could be exploited for example in space applications, where radiation-hard materials are required.

To conclude, the results achieved in this thesis will help to understand and engineer the properties of Si-QDs whose application potential has increased after several years of research both at the ensemble and at the single-dot level.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 77
Series
TRITA-SCI-FOU ; 2018:47
Keywords
silicon, nanocrystals, quantum dots, photoluminescence, optics, emission, absorption
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-238859 (URN)978-91-7873-027-8 (ISBN)
Public defence
2018-12-07, Sal A, Electrum building, 2nd floor, Kistagången 16, Kista (Stockholm), 10:00 (English)
Opponent
Supervisors
Note

QC 20181114

Available from: 2018-11-14 Created: 2018-11-13 Last updated: 2018-11-14Bibliographically approved

Open Access in DiVA

No full text in DiVA

Other links

Publisher's full textScopus

Authority records BETA

Pevere, FedericoSychugov, IlyaSangghaleh, FatemehLinnros, Jan

Search in DiVA

By author/editor
Pevere, FedericoSychugov, IlyaSangghaleh, FatemehFucikova, AnnaLinnros, Jan
By organisation
Material Physics, MFMaterials- and Nano Physics
In the same journal
The Journal of Physical Chemistry C
Other Chemistry Topics

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 118 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf