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Exciton-phonon coupling in single quantum dots with different barriers
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
Tyndall National Institute, University College Cork, Ireland.
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-4547-6673
Tyndall National Institute, University College Cork, Ireland.
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2011 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 25, 251911- p.Article in journal (Refereed) Published
Abstract [en]

The coupling between longitudinal-optical (LO) phonons and neutral excitons in two different kinds of InGaAs pyramidal quantum dots embedded in either AlGaAs or GaAs barriers is experimentally examined. We find a slightly weaker exciton-LO-phonon coupling and increased linewidth of the phonon replicas for the quantum dots with GaAs barriers compared to the ones with AlGaAs barriers. These results, combined with the fact that the LO-phonon energy of the exciton is the same for both kinds of dots, are taken as evidence that the excitons mainly couple to LO-phonons within the QDs.

Place, publisher, year, edition, pages
American Institute of Physics , 2011. Vol. 98, no 25, 251911- p.
Keyword [en]
aluminium compounds; gallium arsenide; III-V semiconductors; indium compounds; phonon-exciton interactions; semiconductor quantum dots
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-67198DOI: 10.1063/1.3600781ISI: 000292039900027OAI: oai:DiVA.org:liu-67198DiVA: diva2:408225
Note
Original Publication: Daniel Dufåker, L. O. Mereni, Fredrik K. Karlsson, V. Dimastrodonato, G. Juska, Per-Olof Holtz and E. Pelucchi, Exciton-phonon coupling in single quantum dots with different barriers, 2011, Applied Physics Letters, (98), 25, 251911. http://dx.doi.org/10.1063/1.3600781 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2011-04-04 Created: 2011-04-04 Last updated: 2015-01-23
In thesis
1. Spectroscopy studies of few particle effects in pyramidal quantum dots
Open this publication in new window or tab >>Spectroscopy studies of few particle effects in pyramidal quantum dots
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis work two very similar processes have been studied both involving excitations of particles during recombination of exciton complexes in quantum dots, reducing the energy of the emitted photon. Different exciton complexes are defined according to the number of electrons and holes in the quantum dot upon recombination. The neutral exciton complexes with one electron and one hole (X) and two electrons and two (X+) holes respectively are referred to as the exciton andthe biexciton. Accordingly the charged exciton complexes consisting of two electrons and one hole (X) and one electron and two holes (X+), respectively, are referred to as negatively- and positively charged excitons, respectively. Whenever another particle is excited during the recombination of one electron-hole pair within these complexes, the result is a weak satellite peak, spectrally redshifted with respect to the main emission peaks related to the exciton complex.

In the first part of this thesis work, described in the first two papers, the exciton-LO-phonon interaction is studied with a weak redshifted satellite peak as the signature, referred to as a phonon replica. The intensity ratio between the replicas and the corresponding main emission were determined from the obtained microphotoluminescencespectra. It was found that this ratio was significantly weaker for the positively charged exciton X+ compared to the neutral exciton, X, and the negatively charged exciton, X. This experimentally obtained result was further supported by computations. Interestingly, the computations revealed that despite that X+ displays the weakest phonon replica among the investigated complexes, it possesses the strongest Fröhlich coupling to phonons in the lattice before recombination. In addition, the spectral broadening of the phonon replicas compared to the main emission is discussed. Also, the origin of the exciton-LO-phonon coupling is concluded to be from the QD itself, based on a comparison between quantum dots with different barriers.

In the last paper an additional weak redshifted satellite peak in the recombination spectra is studied. The intensity of this weak satellite peak is correlated to the peak intensity of the positively charged exciton, X+, main emission peak. In addition to this photoluminescence excitation experiments, magnetic field measurement and calculations further support our interpretation that the satellite peak is related to the shake-up of the ground-state hole in the QD that is not involved in the optical recombination. This hole is thus excited by Coulomb interaction to an excited state yielding a photon energy reduced with the difference between the ground-state and the excited state of the spectator hole.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 31 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1478Studies in Science and Technology Education, ISSN 1652-5051 ; 38
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-67199 (URN)LIU-TEK-LIC-2011:17 (Local ID)978-91-7393-179-3 (ISBN)LIU-TEK-LIC-2011:17 (Archive number)LIU-TEK-LIC-2011:17 (OAI)
Presentation
2011-04-29, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 13:15 (English)
Supervisors
Available from: 2011-04-04 Created: 2011-04-04 Last updated: 2015-01-23Bibliographically approved
2. Few particle effects in pyramidal quantum dots - a spectroscopic study
Open this publication in new window or tab >>Few particle effects in pyramidal quantum dots - a spectroscopic study
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis two very similar processes have been studied, both involving excitations of particles during recombination of exciton complexes in quantum dots, reducing the energy of the emitted photon. Different exciton complexes are defined according to the number of electrons and holes in the quantum dot upon recombination. The neutral exciton complexes with one electron and one hole (X) and two electrons and two holes (2X) respectively are referred to as the exciton and the biexciton. Accordingly the charged exciton complexes consisting of two electrons and one hole (X) and one electron and two holes (X+), respectively, are referred to as negatively and positively charged excitons, respectively. Whenever another particle is excited during the recombination of one electron-hole pair within these complexes, the result is a weak satellite peak, spectrally redshifted with respect to the main emission peak related to the exciton complex.

In the first part of this thesis, described in papers 1 - 3, the first and second order exciton-LO-phonon interaction is studied with weak satellite peaks, redshifted by the LOphonon energy (ћωLO or 2ћωLO), as the signature, referred to as phonon replicas. The intensity ratio between the first order replicas and the corresponding main emission were determined from the obtained micro-photoluminescence spectra. It was found that this ratio was significantly weaker for the positively charged exciton X+ compared to the neutral exciton, X, and the negatively charged exciton, X. This experimentally obtained result was further supported by computations. Interestingly, the computations revealed that despite that X+ displays the weakest phonon replica among the investigated complexes, it possesses the strongest Fröhlich coupling to phonons in the lattice before recombination. The spectral broadening of the phonon replicas compared to the main emission is also discussed. The origin of the exciton-LO-phonon coupling is concluded to be from within the quantum dot (QD) itself, based on a comparison between quantum dots with different barriers. In addition, the measured intensity of the second order LO-phonon replica was approximately three times stronger than predictions made with the adiabatic Huang-Rhys theory but much weaker than the two orders in magnitude enhancement that was predicted when non adiabatic effects was included.

Symmetrical QDs are a requirement for achieving entangled photon emission, desired for applications within quantum cryptography. In the fourth paper we relate the emission pattern of the doubly positively charged exciton X2+ to the symmetry of the QDs. In particular the splitting between the two low-energy components was found to be a measure of the asymmetry of the QDs. The emission pattern of the doubly charged exciton may then be used as a post-growth uninvasive selection tool were high-symmetry QDs could reliably be selected.

In the last paper an additional weak redshifted satellite peak in the recombination spectra is studied. The intensity of this weak satellite peak is correlated to the peak intensity of the positively charged exciton, X+, main emission peak. In addition to this photoluminescence excitation experiments and computations further support our interpretation that the satellite peak is related to the shake-up of the ground state hole in the QD that is not involved in the optical recombination. This hole is excited by Coulomb interaction to an excited state yielding a photon energy that has been reduced with the difference between the ground state and the excited state of the spectator hole.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 59 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1523
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-91491 (URN)978-91-7519-610-7 (ISBN)
Public defence
2013-06-10, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-05-29 Created: 2013-04-25 Last updated: 2015-01-23Bibliographically approved

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