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Few particle effects in pyramidal quantum dots - a spectroscopic study
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
2013 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Linköping: Linköping University Electronic Press, 2013. , s. 59
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1523
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-91491ISBN: 978-91-7519-610-7 (tryckt)OAI: oai:DiVA.org:liu-91491DiVA, id: diva2:623926
Disputas
2013-06-10, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2013-05-29 Laget: 2013-04-25 Sist oppdatert: 2019-12-03bibliografisk kontrollert
Delarbeid
1. Phonon replicas of charged and neutral exciton complexes in single quantum dots
Åpne denne publikasjonen i ny fane eller vindu >>Phonon replicas of charged and neutral exciton complexes in single quantum dots
Vise andre…
2010 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 20Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
American Physical Society, 2010
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-63146 (URN)10.1103/PhysRevB.82.205421 (DOI)000284205500004 ()
Merknad

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/

Tilgjengelig fra: 2010-12-13 Laget: 2010-12-13 Sist oppdatert: 2017-12-11bibliografisk kontrollert
2. Exciton-phonon coupling in single quantum dots with different barriers
Åpne denne publikasjonen i ny fane eller vindu >>Exciton-phonon coupling in single quantum dots with different barriers
Vise andre…
2011 (engelsk)Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, nr 25, s. 251911-Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
American Institute of Physics, 2011
Emneord
aluminium compounds; gallium arsenide; III-V semiconductors; indium compounds; phonon-exciton interactions; semiconductor quantum dots
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-67198 (URN)10.1063/1.3600781 (DOI)000292039900027 ()
Merknad
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/ Tilgjengelig fra: 2011-04-04 Laget: 2011-04-04 Sist oppdatert: 2017-12-11
3. Evidence of nonadiabatic exciton-phonon interaction probed by second-order LO-phonon replicas of single quantum dots
Åpne denne publikasjonen i ny fane eller vindu >>Evidence of nonadiabatic exciton-phonon interaction probed by second-order LO-phonon replicas of single quantum dots
Vise andre…
2013 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, nr 8Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

In this experimental study of single InGaAs/GaAs quantum dots (QDs) the photoluminescence intensity of the second order LO-phonon replica of the excitonic interband recombination was measured along with the intensities of the first and zeroth orders. The results show that the intensity of the second-order replica is three to four times stronger than expected from the adiabatic Huang-Rhys theory, indicating that the neglected nonadiabaticity plays an important role for the understanding of the exciton-phonon coupling in QDs.

sted, utgiver, år, opplag, sider
American Physical Society, 2013
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-90677 (URN)10.1103/PhysRevB.87.085317 (DOI)000315375700011 ()
Merknad

Funding Agencies|Science Foundation Ireland|05/IN.1/I2510/IN.1/I3000|Swedish Research Council (VR)||K. A. Wallenberg Foundation||Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU)|2009-00971|

Tilgjengelig fra: 2013-04-05 Laget: 2013-04-03 Sist oppdatert: 2017-12-06bibliografisk kontrollert
4. Quantum dot asymmetry and the nature of excited hole states probed by the doubly positively charged exciton X2+
Åpne denne publikasjonen i ny fane eller vindu >>Quantum dot asymmetry and the nature of excited hole states probed by the doubly positively charged exciton X2+
Vise andre…
2013 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, nr 4Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

In this experimental and theoretical study, it was found that the emission pattern of the doubly positively charged exciton complex X2+ strongly depends on the nature of the involved excited hole states as well as the quantum dot symmetry. The two-hole system in the final state of the X2+ recombination for the investigated high-symmetry pyramidal InGaAs quantum dots does not exhibit the singlet-tripletlike arrangement previously observed for the two-electron counterpart. Instead, the final states exhibit two true doublets, in accordance with group-theoretical predictions. Asymmetry is manifested in the photoluminescence spectra of X2+ by a significant splitting of one doublet, which is a spectral feature exhibited to some degree by all of the measured quantum dots. The analysis demonstrates that an external magnetic field elevates the symmetry of the quantum dots. This work highlights the exciton complex X2+ as a very sensitive probe of the quantum dot shape as well as the nature of the involved quantum states. Thus, its spectral features are very suitable for an efficient uninvasive postgrowth symmetry characterization of quantum dots.

HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-92307 (URN)10.1103/PhysRevB.88.045321 (DOI)000322575500009 ()
Tilgjengelig fra: 2013-05-08 Laget: 2013-05-08 Sist oppdatert: 2017-12-06bibliografisk kontrollert
5. Hole Shake-Up in Individual InGaAs Quantum Dots
Åpne denne publikasjonen i ny fane eller vindu >>Hole Shake-Up in Individual InGaAs Quantum Dots
Vise andre…
(engelsk)Manuskript (preprint) (Annet vitenskapelig)
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.

HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-64726 (URN)
Tilgjengelig fra: 2011-02-03 Laget: 2011-02-03 Sist oppdatert: 2016-06-07bibliografisk kontrollert

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