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Synthesis and properties of single luminescent silicon quantum dots
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0003-2562-0540
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.
Series
Trita-ICT/MAP, 2007:1
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-4254ISBN: 91-7178-533-7 (print)OAI: oai:DiVA.org:kth-4254DiVA: diva2:11484
Public defence
2007-01-19, Aula N2, Electrum-3, Isafjordsgatan 28, Kista, 10:15
Opponent
Supervisors
Note
QC 20100922Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2011-10-11Bibliographically approved
List of papers
1. Narrow luminescence linewidth of a silicon quantum dot
Open this publication in new window or tab >>Narrow luminescence linewidth of a silicon quantum dot
2005 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 94, no 8, 087405 (1)-087405 (4) p.Article in journal (Refereed) Published
Abstract [en]

Single-dot luminescence spectroscopy was used to study the emission linewidth of individual silicon nanocrystals from low temperatures up to room temperature. The results show a continuous line narrowing towards lower temperatures with a linewidth as sharp as 2 meV at 35 K. This value, clearly below the thermal broadening at this temperature, proves the atomiclike emission from silicon quantum dots subject to quantum confinement. The low temperature measurements further reveal a similar to6 meV replica, whose origin is discussed. In addition, an similar to60 meV TO-phonon replica was detected, which is only present in a fraction of the dots.

Place, publisher, year, edition, pages
American Physical Society, 2005
Keyword
electron-phonon interactions, photoluminescence spectroscopy, semiconductor nanocrystals, porous silicon, confinement
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6697 (URN)10.1103/PhysRevLett.94.087405 (DOI)000227386000066 ()2-s2.0-18144403210 (Scopus ID)
Note
QC 20100922Available from: 2012-01-11 Created: 2006-12-29 Last updated: 2012-01-11Bibliographically approved
2. Luminescence blinking of a Si quantum dot in a SiO2 shell
Open this publication in new window or tab >>Luminescence blinking of a Si quantum dot in a SiO2 shell
2005 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 11, 115331-1-115331-5 p.Article in journal (Refereed) Published
Abstract [en]

The phenomenon of on-off luminescence intermittency - blinking - in silicon nanocrystals was studied using a single-dot microphotoluminescence technique. From recordings of the luminescence intensity trace, on- and off-time distributions were extracted revealing exponential behavior, as expected for systems with blinking of a purely random nature. The corresponding switching rates for on-off and off-on processes exhibit different dependence on the excitation intensity. While the on-off switching rate grows quadratically with the excitation, the inverse process is nearly pumping power independent. Experimental findings are interpreted in terms of a dot "charging" model, where a carrier may become trapped in the surrounding matrix due to thermal and Auger-assisted processes. Observed blinking kinetics appear to be different from that of porous silicon particles.

Place, publisher, year, edition, pages
The American Physical Society, 2005
Keyword
silicon, silicon dioxide, analytic method, article, comparative study, crystal structure, kinetics, luminescence, mathematical model, photoluminescence, quantum dot, recording
National Category
Condensed Matter Physics Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6698 (URN)10.1103/PhysRevB.71.115331 (DOI)000228065500106 ()2-s2.0-20044378177 (Scopus ID)
Note
QC 20100921Available from: 2012-01-18 Created: 2006-12-29 Last updated: 2012-01-18Bibliographically approved
3. Effect of substrate proximity on luminescence yield from Si nanocrystals
Open this publication in new window or tab >>Effect of substrate proximity on luminescence yield from Si nanocrystals
Show others...
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
Keyword
Density (optical), Photoluminescence, Quantum efficiency, Refractive index, Semiconductor quantum dots, Silicon
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6699 (URN)10.1063/1.2226976 (DOI)000240545400024 ()2-s2.0-33748701270 (Scopus ID)
Note
QC 20100910Available from: 2012-01-13 Created: 2006-12-29 Last updated: 2012-01-13Bibliographically approved
4. Single dot optical spectroscopy of silicon nanocrystals: Low temperature measurements
Open this publication in new window or tab >>Single dot optical spectroscopy of silicon nanocrystals: Low temperature measurements
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2005 (English)In: Optical materials (Amsterdam), ISSN 0925-3467, Vol. 27, no 5, 973-976 p.Article in journal (Refereed) Published
Abstract [en]

Single dot spectroscopy allows studying properties of a single nanocrystal avoiding inhomogeneous broadening of the emission band. Here, data obtained by this technique for Si nanocrystals fabricated by electron beam lithography, plasma etching and subsequent size-reduction by oxidation are presented. First, blinking (on–off intermittence) of the luminescence was observed for most individual nanocrystals, although some exhibited relatively stable luminescence. As a result of the quantum confinement effect spectra with different emission wavelengths for different nanocrystals were recorded. While at room temperature the full width at half-maximum of the nanocrystal emission peaks was measured to be 100–150 meV, at 80 K the linewidth for some dots appeared to be about 25 meV only. The observed temperature dependence of the homogeneous linewidth may lead to an understanding of the exciton–phonon interaction in indirect band-gap quantum dots.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-6700 (URN)10.1016/j.optmat.2004.08.046 (DOI)000227621300048 ()2-s2.0-13444273345 (Scopus ID)
Note
QC 20100922 QC 20111011. Symposium of the European-Materials-Research-Society on Si-Based Photonics - Towards True Monolithic Integration. Strasbourg, FRANCE. MAY 25-28, 2004. Tidigare titel: Single dot optical spectroscopy of silicon nanocrystals: Low-T measurements Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2011-10-11Bibliographically approved
5. Light emission from silicon nanocrystals: probing a single quantum do
Open this publication in new window or tab >>Light emission from silicon nanocrystals: probing a single quantum do
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2006 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, no 15, 5249-5253 p.Article in journal (Refereed) Published
Abstract [en]

Analysis of low-temperature photoluminescence measurements performed on single silicon nanocrystals is presented. The luminescence emission linewidth of Si nanocrystals is found to be less than thermal broadening at low temperature, confirming the atomic-like nature of their energetic states. Beside the main peak the low-temperature spectra reveal a similar to 6 meV replica, the origin of which is discussed. For some of the investigated dots, we also observe a similar to 60 meV transverse optical (TO) phonon replica. The regular arrangement of individual nanocrystals used in this work enables combined high-resolution transmission electron microscopy (TEM) and low-temperature photoluminescence characterization of the same single quantum dot.

Place, publisher, year, edition, pages
Elsevier, 2006
Keyword
silicon nanocrystal, luminescence, electron-phonon interactions, semiconductor nanocrystals
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-6701 (URN)10.1016/j.apsusc.2005.12.030 (DOI)000238623300003 ()2-s2.0-33744533732 (Scopus ID)
Conference
8th International Conference on Atomically Controlled Surfaces, Interfaces, and Nanostructures/13th International Congress on Thin Films Stockholm, SWEDEN, JUN 20-23, 2005
Note
QC 20100922. Conference: 8th International Conference on Atomically Controlled Surfaces, Interfaces, and Nanostructures/13th International Congress on Thin Films. Stockholm, SWEDEN. JUN 20-23, 2005 Available from: 2012-01-27 Created: 2006-12-29 Last updated: 2012-01-27Bibliographically approved
6. Structural imaging of a Si quantum dot: Towards combined PL and TEM characterization
Open this publication in new window or tab >>Structural imaging of a Si quantum dot: Towards combined PL and TEM characterization
2006 (English)In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 121, no 2, 353- p.Article in journal (Refereed) Published
Abstract [en]

Individual silicon quantum dots were fabricated by electron-beam lithography, plasma etching and a two-step oxidation process. This enables photoluminescence (PL) from individual dots at various temperatures to be detected and spectrally resolved using a sensitive charge-coupled device camera-imaging system, as reported previously. The regular array-like arrangement of oxidized pillars containing individual nanocrystals, in principle, enables combined transmission electron microscopy (TEM) and low-temperature PL characterization of the same Si quantum dot. To this end, a technique employing focused ion beam was developed for preparation of the pillar/nanocrystal of interest for TEM. It is shown that silicon quantum dots of several nanometers in size can be characterized using such a method.

Keyword
Silicon nanocrystal, Luminescence
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-6702 (URN)10.1016/j.jlumin.2006.08.061 (DOI)000242751200039 ()2-s2.0-33750377121 (Scopus ID)
Note
Tidigare titel: Structural and optical properties of a single silicon quantum dot: towards combined PL and TEM characterization. Conference: Symposium on Si-based Photonics held at the EMRS 2006 Conference. Nice, FRANCE. MAY 29-JUN 02, 2006. QC 20100922Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2011-09-29Bibliographically approved

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