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Spectroscopy studies of few particle effects in pyramidal quantum dots
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-67199Local ID: LIU-TEK-LIC-2011:17ISBN: 978-91-7393-179-3OAI: oai:DiVA.org:liu-67199DiVA: diva2:408242
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
List of papers
1. Phonon replicas of charged and neutral exciton complexes in single quantum dots
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 20Article in journal (Refereed) Published
Abstract [en]

The longitudinal-optical (LO)-phonon coupling is experimentally examined by the optical decay of various charged and neutral exciton species in single quantum dots, and the related Huang-Rhys parameters are extracted. A positive trion exhibits significantly weaker LO-phonon replicas in the photoluminescence spectrum than the neutral and negatively charged species. Model computations show that the strength of the replicas is determined by the Coulomb interactions between electrons and holes, which modify the localization of the envelope wave functions and the net charge distribution.

Place, publisher, year, edition, pages
American Physical Society, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-63146 (URN)10.1103/PhysRevB.82.205421 (DOI)000284205500004 ()
Note

Original Publication: Daniel Dufåker, Fredrik Karlsson, V Dimastrodonato, L O Mereni, Bo Sernelius, Per-Olof Holtz and E Pelucchi, Phonon replicas of charged and neutral exciton complexes in single quantum dots, 2010, PHYSICAL REVIEW B, (82), 20, 205421. http://dx.doi.org/10.1103/PhysRevB.82.205421 Copyright: American Physical Society http://www.aps.org/

Available from: 2010-12-13 Created: 2010-12-13 Last updated: 2015-01-23Bibliographically approved
2. Exciton-phonon coupling in single quantum dots with different barriers
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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
Keyword
aluminium compounds; gallium arsenide; III-V semiconductors; indium compounds; phonon-exciton interactions; semiconductor quantum dots
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-67198 (URN)10.1063/1.3600781 (DOI)000292039900027 ()
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
3. Hole Shake-Up in Individual InGaAs Quantum Dots
Open this publication in new window or tab >>Hole Shake-Up in Individual InGaAs Quantum Dots
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We report on a spectroscopic study of hole shake-up processes in single InGaAs quantum dots. By studying dots with very high luminescence efficiency these processes are unveiled and further tested in an applied magnetic field. The mechanism is attributed to shake-up of a hole from the S ground state to the D excited state. The experimental results are confirmed by configuration interaction calculations that also reveal a dependence of the shake-up intensity on the relative extension of electron and hole wave functions.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-64726 (URN)
Available from: 2011-02-03 Created: 2011-02-03 Last updated: 2016-06-07Bibliographically approved

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