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Narrow luminescence linewidth of a silicon quantum dot
KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.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.ORCID iD: 0000-0002-5260-5322
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. Vol. 94, no 8, 087405 (1)-087405 (4) p.
Keyword [en]
electron-phonon interactions, photoluminescence spectroscopy, semiconductor nanocrystals, porous silicon, confinement
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-6697DOI: 10.1103/PhysRevLett.94.087405ISI: 000227386000066Scopus ID: 2-s2.0-18144403210OAI: oai:DiVA.org:kth-6697DiVA: diva2:11478
Note
QC 20100922Available from: 2012-01-11 Created: 2006-12-29 Last updated: 2012-01-11Bibliographically 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.
Series
Trita-ICT/MAP, 2007:1
National Category
Condensed Matter Physics
Identifiers
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
Opponent
Supervisors
Note
QC 20100922Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2011-10-11Bibliographically approved
2. Silicon nanowires, nanopillars and quantum dots: Fabrication and characterization
Open this publication in new window or tab >>Silicon nanowires, nanopillars and quantum dots: Fabrication and characterization
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Semiconductor nanotechnology is today a very well studied subject, and demonstrations of possible applications and concepts are abundant. However, well-controlled mass-fabrication on the nanoscale is still a great challenge, and the lack of nanofabrication methods that provide the combination of required fabrication precision and high throughput, limits the large-scale use of nanodevices. This work aims in resolving some of the issues related to nanostructure fabrication, and deals with development of nanofabrication processes, the use of size-reduction for reaching true nanoscale dimensions (20 nm or below), and finally the optical and electrical characterization to understand the physics of the more successful structures and devices in this work. Due to its widespread use in microelectronics, silicon was the material of choice throughout this work.

Initially, a fabrication process based on electron beam lithography (EBL) was designed, allowing controlled fabrication of devices of dimensions down to 30 nm, although, generally, initial device dimensions were above 70 nm, allowing the flexible but low-throughput EBL, to be replaced by state-of-the-art optical lithography in the case of industrialization of the process. A few main processes were developed throughout the course of this work, which were capable of defining silicon nanopillar and nano-wall arrays from bulk silicon, and silicon nanowire devices from silicon-on-insulator (SOI) material.

Secondly, size-reduction, as a means of providing access to few-nanometer dimensions not available by current lithography techniques was investigated. An additional goal of the size-reduction studies was to find self-limiting mechanisms in the process, that would limit the impact of variations in the size and other imperfections of the initial structures. Thermal oxidation was investigated mainly for self-limited size-reduction of silicon nanopillars, resulting in well-defined quantum dot arrays of few-nm dimensions. Electrochemical etching was employed to size-reduce both silicon nanopillars and silicon nanowires down into the 10-nm regime. This being a novel application, a more thorough study of electrochemical etching of low-dimensional and thin-layer structures was performed as well as development of a micro-electrochemical cell, enabling electrochemical etching of fabricated nanowire devices with improved control.

Finally, the combination of nanofabrication and size-reduction resulted in two successful device structures: Sparse and spatially well-controlled single silicon quantum dot arrays, and electrically connected size-reduced silicon nanowires. The quantum dot arrays were investigated through photoluminescence spectroscopy demonstrating for the first time atomic-like photoemission from single silicon quantum dots. The silicon nanowire devices were electrically characterized. The current transport through the device was determined to be through inversion layer electrons with surface states of the nanowire surfaces greatly affecting the conductance of the nanowire. A model was also proposed, capable of relating physical and electrical properties of the nanowires, as well as demonstrating the considerable influence of charged surface states on the nanowire conductance.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. ix, 98 p.
Series
Trita-FTE, ISSN 0284-0545 ; 2005:4
Keyword
Silicon nanowires, silicon nanopillars, silicon quantum dots, size-reduction, thermal oxidation, electrochemical etching of silicon, photoluminescence
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-420 (URN)
Public defence
2005-09-27, C1, KTH-Electrum, Isafjordsgatan 26, Kista, 10:15
Opponent
Supervisors
Note
QC 20101101Available from: 2005-09-15 Created: 2005-09-15 Last updated: 2010-11-01Bibliographically approved

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Sychugov, IlyaLinnros, Jan

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