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Polarization of photoluminescence excitation and emission spectra of silicon nanorods within single Si/SiO2 nanowires
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.ORCID iD: 0000-0002-5260-5322
2011 (English)In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 8, no 3, 1017-1020 p.Article in journal (Refereed) Published
Abstract [en]

Polarization properties of individual silicon nanowires are studied using an optical micro-spectroscopy setup equipped with a Fresnel rhomb to rotate the polarization of the exciting laser and the analyzer to characterize the polarization of emitted photoluminescence. The Si nanowire samples are prepared by electron-beam lithography, plasma etching and oxidation. The fabricated wires are embedded in SiO2 and oriented parallel to the Si substrate. Due to the fluctuating wire diameter (around 5 nm) the very long wires (several tens of μm) are effectively divided into an array of quantum rods (prolate ellipsoids). These structures have strong photoluminescence under UV-blue excitation at room temperature. The degree of photoluminescence linear polarization of both excitation and emission is very high, between 0.9-1, and reveals relatively low fluctuations at different spots of the wires. Experimental results are compared with available theoretical models leading to the conclusion that the high polarization degree is mostly due to surface charges (dielectric confinement) with smaller contribution of quantum confinement effects.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2011. Vol. 8, no 3, 1017-1020 p.
Keyword [en]
Luminescence, Nanorod, Nanowire, Polarization, Silicon
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-49809DOI: 10.1002/pssc.201000398ISI: 000301537100087ScopusID: 2-s2.0-79952675785OAI: diva2:460344
QC 20111130Available from: 2012-03-21 Created: 2011-11-29 Last updated: 2012-09-20Bibliographically approved
In thesis
1. Fabrication and characterization of single luminescing quantum dots from 1D silicon nanostructures
Open this publication in new window or tab >>Fabrication and characterization of single luminescing quantum dots from 1D silicon nanostructures
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon as a mono-crystalline bulk semiconductor is today the predominant material in many integrated electronic and photovoltaic applications. This has not been the case in lighting technology, since due to its indirect bandgap nature bulk silicon is an inherently poor light emitter.With the discovery of efficient light emission from silicon nanostructures, great new interest arose and research in this area increased dramatically.However, despite more than two decades of research on silicon nanocrystals and nanowires, not all aspects of their light emission mechanisms and optical properties are well understood, yet.There is great potential for a range of applications, such as light conversion (phosphor substitute), emission (LEDs) and harvesting (solar cells), but for efficient implementation the underlying mechanisms have to be unveiled and understood.Investigation of single quantum emitters enable proper understanding and modeling of the nature and correlation of different optical, electrical and geometric properties.In large numbers, such sets of experiments ensure statistical significance. These two objectives can best be met when a large number of luminescing nanostructures are placed in a pattern that can easily be navigated with different measurement methods.This thesis presents a method for the (optional) simultaneous fabrication of luminescent zero- and one-dimensional silicon nanostructuresand deals with their structural and optical characterization.Nanometer-sized silicon walls are defined by electron beam lithography and plasma etching. Subsequent oxidation in the self-limiting regime reduces the size of the silicon core unevenly and passivates it with a thermal oxide layer.Depending on the oxidation time, nanowires, quantum dots or a mixture of both types of structures can be created.While electron microscopy yields structural information, different photoluminescence measurements, such as time-integrated and time-resolved imaging, spectral imaging, lifetime measurements and absorption and emission polarization measurements, are used to gain knowledge about optical properties and light emission mechanisms in single silicon nanocrystals.The fabrication method used in this thesis yields a large number of spatially separated luminescing quantum dots randomly distributed along a line, or a slightly smaller number that can be placed at well-defined coordinates. Single dot measurements can be performed even with an optical microscope and the pattern, in which the nanostructures are arranged, enables the experimenter to easily find the same individual dot in different measurements.Spectral measurements on the single dot level reveal information about processes that are involved in the photoluminescence of silicon nanoparticles and yield proof for the atomic-like quantized nature of energy levels in the conduction and valence band, as evidenced by narrow luminescence lines (~500 µeV) at low temperature. Analysis of the blinking sheds light on the charging mechanisms of oxide-capped Si-QDs and, by exposing exponential on- and off-time distributions instead of the frequently observed power law distributions, argues in favor of the absence of statistical aging. Experiments probing the emission intensity as a function of excitation power suggest that saturation is not achieved. Both absorption and emission of silicon nanocrystals contained in a one-dimensional silicon dioxide matrix are polarized to a high degree. Many of the results obtained in this work seem to strengthen the arguments that oxide-capped silicon quantum dots have universal properties, independently of the fabrication method, and that the greatest differences between individual nanocrystals are indeed caused by individual factors like local environment, shape and size (among others).

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xv, 60 p.
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:15
silicon, quantum dot, nanocrystal, nanowire, nanostructure, photoluminescence
National Category
Physical Sciences
urn:nbn:se:kth:diva-102524 (URN)978-91-7501-486-9 (ISBN)
Public defence
2012-10-12, Sal E, Forum KTH-ICT, Isafjordsgatan 39, Kista, 10:00 (English)
Swedish Research Council

QC 20120920

Available from: 2012-09-20 Created: 2012-09-19 Last updated: 2012-09-20Bibliographically approved

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