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Carrier spin dynamics in modulation-doped InAs/GaAs quantum dots
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0002-4606-4865
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
2006 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, no 5, 054310- p.Article in journal (Refereed) Published
Abstract [en]

Photoexcited electron and hole spin relaxation was studied in modulation-doped and undoped InAs/GaAs quantum dots by means of time-resolved photoluminescence. After excitation into the barriers or the wetting layer, the electron spin polarization is preserved during the capture and relaxation in the dots, especially in the p-doped structures, and decays with a characteristic time of about 100 ps. Spin state admixture in combination with electron interaction with acoustic phonons is suggested as the spin relaxation mechanism. Rapid spin polarization decay during carrier relaxation in undoped quantum dots is attributed to electron-optical phonon interaction. For carrier excitation directly into the dots, no significant spin polarization was observed, which points to the mixed nature of hole levels in quantum dots. The hole spin polarization randomizes on a much shorter time scale and is not detected in the experiment.

Place, publisher, year, edition, pages
2006. Vol. 100, no 5, 054310- p.
Keyword [en]
Electrons, Polarization, Relaxation processes, Semiconducting gallium arsenide, Semiconducting indium compounds, Wetting
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-5879DOI: 10.1063/1.2337776ISI: 000240602500103ScopusID: 2-s2.0-33748846722OAI: diva2:10406
QC 20100902. Uppdaterad från In press till Published (20100902)Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2010-09-02Bibliographically 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.
Trita-ICT/MAP, 2006:1
quantum dots, photoluminescence, time-resolved, spectroscopy, semiconductor
National Category
Atom and Molecular Physics and Optics
urn:nbn:se:kth:diva-4019 (URN)
Public defence
2006-06-13, C1, Electrum, Isafjordsgatan 22, Kista, 10:15
QC 20100920Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2010-09-20Bibliographically approved

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