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Reversed quantum-confined Stark effect and an asymmetric band alignment observed for type-II Si∕Ge quantum dots
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
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2005 (English)In: Physical Review B, ISSN 1098-0121, Vol. 71, no 11, 113301- p.Article in journal (Refereed) Published
Abstract [en]

We report on the quantum-confined Stark effect for spatially indirect transitions in Stranski-Krastanov grown type-II Si∕Ge quantum dots. A linear blueshift of the spatially indirect transition is observed at increasing electric field in contrast to the commonly observed redshift for type-I transitions. A shift of the emission-peak position and different quenching rates of the photoluminescence for p-i-n and n-i-p diodes at increased electric field and temperature indicate a deeper notch potential for electrons above the dot than below due to a strain-induced asymmetry in the band alignment.

Place, publisher, year, edition, pages
2005. Vol. 71, no 11, 113301- p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-16331DOI: 10.1103/PhysRevB.71.113301OAI: oai:DiVA.org:liu-16331DiVA: diva2:133870
Note

Original Publication: Mats Larsson, Per-Olof Holtz, Anders Elfving, Göran Hansson and Wei-Xin Ni, Reversed quantum-confined Stark effect and an asymmetric band alignment observed for type-II Si∕Ge quantum dots, 2005, Physical Review B, (71), 113301. http://dx.doi.org/10.1103/PhysRevB.71.113301 Copyright: American Physical Society http://www.aps.org/

Available from: 2009-01-15 Created: 2009-01-15 Last updated: 2012-12-11Bibliographically approved
In thesis
1. Spectroscopy of semiconductor quantum dots
Open this publication in new window or tab >>Spectroscopy of semiconductor quantum dots
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum dots in the Si/Ge and InAs/GaAs materials systems are examined by means of photoluminescence. The spectroscopic study of Si/Ge quantum dots has demonstrated two different radiative recombination channels in the type II band alignment: The spatially direct transition inside the dot and the spatially indirect transition across the dot interface. Increased sample temperature results in a gradual transfer from the spatially indirect to the spatially direct recombination due to higher oscillator strength combined with the increased electron population inside the dot. In contrast to the spatially direct transition, the spatially indirect transition is shown to be sensitive to the carrier density due to the band bending at the Si/Ge interface. Due to an increased Si/Ge intermixing and hence reduced strain in the Si barrier, a reduction of the conduction band offset at increased growth temperatures is observed utilizing the different recombination channels as probes. The optical properties as derived from photoluminescence are correlated with the structural properties obtained by atomic force microscopy. Furthermore, by applying an electric field across the Si/Ge quantum dot structure, a reversed quantum confined Stark effect is demonstrated for the spatially indirect transition. By switching between the two different field directions, unique information on the growth related asymmetric strain profile derived at the through self-assembly of the quantum dots can be gained since corresponding information can not be obtained for type I systems.

The studies of the InAs/GaAs quantum dots show that external electric and magnetic fields alter the in-plane carrier transport to the dots. The results obtained from the micro-photoluminescence exciton spectra of a single dot demonstrate a redistribution of the excitonic lines when a lateral electric field is applied. This fact exhibits an effective charge reconfiguration of the dot from a purely negative charge state to a neutral state, demonstrating that the number of electrons and holes are controlled by the electric field. The model proposed to explain the charge redistribution is based on an effective hole localization at the potential fluctuations of the wetting layer at low temperatures and low fields. Furthermore, it is demonstrated that the quantum dot photoluminescence signal is considerably increased (up to a factor of 4) depending on the magnitude of the external electric field. The experimental results also show that the internal field is altered by an additional infrared illumination of the sample. An applied magnetic field perpendicular to the quantum dot layer at low temperatures is found to enhance the carrier localization in the wetting layer and accordingly reduce the quantum dot photoluminescence intensity. At higher temperatures (>100K), an enhanced photoluminescence intensity is instead observed due to increased capture, localization, and recombination rate of the carriers in the quantum dots.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. 65 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 976
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-31204 (URN)16952 (Local ID)91-85457-48-5 (ISBN)16952 (Archive number)16952 (OAI)
Public defence
2005-11-18, Hörsal Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-12-11

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Larsson, MatsHoltz, Per-OlofElfving, AndersHansson, GöranNi, Wei-Xin

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