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Photoexcited carrier dynamics in aligned InAs/GaAs quantum dots grown on strain-relaxed InGaAs layers
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.ORCID iD: 0000-0002-4606-4865
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2003 (English)In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 18, no 4, 541- p.Article in journal (Refereed) Published
Abstract [en]

Carrier dynamics in aligned InAs/GaAs quantum dots (QDs) grown on cross-batched patterns induced by metastable InxGa1-xAs layers have been studied by time-resolved photoluminescence. The low-temperature carrier lifetimes were found to be of the order of 100-200 ps and determined by carrier trapping and nonradiative recombination. Comparisons with control "nonaligned" InAs QDs show remarkable differences in dependence of peak PL intensities on excitation power, and in PL decay times dependences on both temperature and excitation intensities. Possible origin of traps, which determine the carrier lifetimes, is discussed.

Place, publisher, year, edition, pages
2003. Vol. 18, no 4, 541- p.
Keyword [en]
quantum dots, dislocations, lateral alignment, time-resolved photoluminescence
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-5884DOI: 10.1016/S1386-9477(03)00232-7ISI: 000183846300020OAI: oai:DiVA.org:kth-5884DiVA: diva2:10411
Note
QC 20100920Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Carrier dynamics in semiconductor quantum dots
Open this publication in new window or tab >>Carrier dynamics in semiconductor quantum dots
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents results of time-resolved photoluminescence experiments conducted on several different self-assembled InGaAs/GaAs and InAs/GaAs semiconductor quantum dot (QD) structures. Depending on the application in mind, different structural, electronic or optical properties have a different weight of importance.

Fast carrier capture and relaxation is critical for QD based lasers, for example. In this thesis, the influence of surplus carriers, introduced through modulation-doping, is studied. It is shown that carrier capture is essentially unaffected whereas the intradot relaxation mechanisms, at least at low carrier concentrations, are fundamentally different. The phonon mediated cascade relaxation found in the undoped reference sample is replaced by efficient scattering with the built-in carriers in the case of the doped structures.

Moreover, spin relaxation also depends on presence of extra carriers. During energy relaxation via carrier-carrier scattering, the spin polarization is preserved whereas in the undoped sample the strong interaction of relaxing carriers with LO phonons causes spin relaxation. The decay of the ground state spin polarization proceeds at the same rate for doped and undoped structures and is shown to be caused by acoustic phonons, even up to 300 K. While optimizing QD growth for specific applications, it is imperative to evaluate the influence of nonradiative recombination, which is most often detrimental.

While misfit dislocations, deliberately introduced in the substrate, lead to the formation of laterally ordered, uniform dots, these samples are found to suffer from strong nonradiative recombination. Structures with different barrier thicknesses and numerical simulations indicate defects in the vicinity of the QDs as main origin of fast carrier trapping.

On the other hand, it is shown that direct dot doping, compared to barrier doping or undoped structures, causes only minor degradation of the optical properties. Directly doped dots even exhibit a significantly weaker photoluminescence quenching with temperature, making them prospective for devices operating at room temperature.

Finally, the superior proton radiation hardness of QD structures compared to quantum wells is demonstrated, which is due to the three-dimensional confinement. The increase of photoluminescence intensity at low to moderate doses is interpreted as an enhanced carrier transfer into the dots via the defects introduced into the material by the protons.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xiii, 99 p.
Series
Trita-ICT/MAP, 2006:1
Keyword
quantum dots, photoluminescence, time-resolved, spectroscopy, semiconductor
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-4019 (URN)
Public defence
2006-06-13, C1, Electrum, Isafjordsgatan 22, Kista, 10:15
Opponent
Supervisors
Note
QC 20100920Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2010-09-20Bibliographically approved

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Publisher's full texthttp://www.sciencedirect.com/science/article/B6VMT-48R19S8-4/2/7772b3ee1eef9650d13f231df124d264

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Marcinkevičius, Saulius

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