| 1. |
- Holtz, Per-Olof, et al.
(author)
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Optical characterization of individual quantum dots
- 2012
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In: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1472-1475
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Journal article (peer-reviewed)abstract
- Optical characterization of single quantum dots (QDs) by means of micro-photoluminescence (mu PL) will be reviewed. Both QDs formed in the Stranski-Krastanov mode as well as dots in the apex of pyramidal structures will be presented. For InGaAs/GaAs dots, several excitonic features with different charge states will be demonstrated. By varying the magnitude of an external electric or magnetic field and/or the temperature, it has been demonstrated that the transportation of carriers is affected and accordingly the charge state of a single QD can be tuned. In addition, we have shown that the charge state of the QD can be controlled also by pure optical means, i.e. by altering the photo excitation conditions. Based on the experience of the developed InAs/GaAs QD system, similar methods have been applied on the InGaN/GaN QD system. less thanbrgreater than less thanbrgreater thanThe coupling of LO phonons to the QD emission is experimentally examined for both charged and neutral excitons in single InGaAs/GaAs QDs in the apex of pyramidal structures. It is shown that the positively charged exciton exhibits a significantly weaker LO phonon coupling in the mu PL spectra than the neutral and negatively charged species, a fact, which is in consistency with model simulations performed.
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| 2. |
- Dufåker, Daniel, et al.
(author)
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Evidence of nonadiabatic exciton-phonon interaction probed by second-order LO-phonon replicas of single quantum dots
- 2013
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87:8
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Dufåker, Daniel, et al.
(author)
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Exciton-phonon coupling in single quantum dots with different barriers
- 2011
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In: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 98:25, s. 251911-
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Dufåker, Daniel, et al.
(author)
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Phonon replicas of charged and neutral exciton complexes in single quantum dots
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 82:20
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Journal article (peer-reviewed)abstract
- 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.
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| 5. |
- Dufåker, Daniel, et al.
(author)
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Quantum dot asymmetry and the nature of excited hole states probed by the doubly positively charged exciton X2
- 2013
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:4
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Karlsson, K Fredrik, et al.
(author)
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Phonon Coupling to Excitonic Transitions in Single InGaAs/AlGaAs Quantum Dots
- 2011
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In: AIP Conference Proceedings. - : AIP. - 0094-243X.
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Conference paper (peer-reviewed)abstract
- The LO‐phonon coupling is experimentally examined from the optical decay of various charged and neutral exciton species in single quantum dots. A positive trion exhibits significantly weaker LO‐phonon replicas in the photoluminescence spectrum than the neutral and negatively charged species.
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| 7. |
- Larsson, Arvid, 1979-, et al.
(author)
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Hole Shake-Up in Individual InGaAs Quantum Dots
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Other publication (other academic/artistic)abstract
- 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.
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