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Effect of substrate proximity on luminescence yield from Si nanocrystals
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0003-2562-0540
KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
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2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, no 11, 111124- p.Article in journal (Refereed) Published
Abstract [en]

The influence of the proximity of a high refractive index substrate on the luminescence of Si nanocrystals was investigated by time-integrated and time-resolved photoluminescence. The luminescence yield was found to be ∼2.5 times larger for emitters distanced from the substrate compared to those in proximity with the substrate, while luminescence decay measurements revealed only a slight increase in the luminescence lifetime (∼15%). Results are discussed in terms of local density of optical modes surrounding a pointlike light emitter with important implications for the collection efficiency of luminescence and the estimation of internal quantum efficiency for a quantum dot.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2006. Vol. 89, no 11, 111124- p.
Keyword [en]
Density (optical), Photoluminescence, Quantum efficiency, Refractive index, Semiconductor quantum dots, Silicon
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-6699DOI: 10.1063/1.2226976ISI: 000240545400024ScopusID: 2-s2.0-33748701270OAI: diva2:11480
QC 20100910Available from: 2012-01-13 Created: 2006-12-29 Last updated: 2012-01-13Bibliographically approved
In thesis
1. Synthesis and properties of single luminescent silicon quantum dots
Open this publication in new window or tab >>Synthesis and properties of single luminescent silicon quantum dots
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Silicon is an ubiquitous electronic material and the discovery of strong room temperature luminescence from porous Si in 1990 raised hopes it may find a new lease of life in the emerging field of optoelectronics. First, the luminescence was shown to be emitted from nanostructures remained in a porous Si network. Later the same emission was shown from Si nanocrystals and the concept of a Si quantum dot emerged. Yet a number of different models have been proposed for the origin of light emission. Some involved interface states between a Si nanocrystal and the surrounding shell, while others considered the effect of quantum confinement in an indirect bandgap semiconductor.

In this work a single Si nanocrystal was addressed to shed light on the mechanism of luminescence. Nanocrystals were prepared using e-beam lithography with subsequent etching and oxidation of silicon nanopillars. In particular, the non-uniform oxidation in self-limiting regime was successfully used to form a single nanocrystal inside nanopillars. This preparation method allowed optical probing of a single nanocrystal with far-field optics.

Results revealed sharp luminescence spectra at low temperatures with a linewidth less than the corresponding thermal broadening. This property is a signature of energy level discreetness, which is, in turn, a straightforward consequence of the quantum confinement model. Another effect observed was a random on-off blinking, which is also regarded as a hallmark of single fluorescent objects. This effect appeared to be dependent on the excitation power density suggesting the involvement of Auger-assisted ionization in the dynamics of nanocrystal luminescence. In addition, it was shown how a change in the optical mode density affects the main parameters of luminescence from Si nanocrystals, such as the radiative lifetime, the quantum efficiency and the total yield.

Finally, in order to clarify the influence of morphological properties, such as size or shape, of a Si quantum dot on its luminescence, combined low-temperature photoluminescence and transmission electron microscopy investigations were initiated. A method was developed using focused ion beam preparation for such a joint characterization.

To conclude, the work gives support to the quantum confinement effect in explaining the light emission mechanism from nano-sized Si, as well as highlights the importance of morphological structure in the luminescence process.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 55 p.
Trita-ICT/MAP, 2007:1
National Category
Condensed Matter Physics
urn:nbn:se:kth:diva-4254 (URN)91-7178-533-7 (ISBN)
Public defence
2007-01-19, Aula N2, Electrum-3, Isafjordsgatan 28, Kista, 10:15
QC 20100922Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2011-10-11Bibliographically approved

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