ISBN 9783843928816

978-3-8439-2881-6, Reihe Physik

Daniel R. Stephan
Inter-sublevel dynamics in single InAs/GaAs quantum dots probed by strong terahertz excitation

122 Seiten, Dissertation Technische Universität Dresden (2016), Softcover, A5

Zusammenfassung / Abstract

In this thesis, the response of single self-assembled quantum dots to strong terahertz pulses is investigated by measuring the emitted photoluminescence spectrally as well as in a time-resolved manner, revealing the dynamics of the sys- tem. Experimentally, this is realized by combining the micro-photoluminescence technique with illumination from a free-electron laser, which provides intense, tunable narrow-band terahertz pulses. The photoluminescence is triggered by spectrally tunable near-infrared illumination with a synchronized, mode-locked titanium sapphire laser. The measured transients are evaluated with a rate-equation model, taking into account the precise detector response. These measurements reveal three distinct effects, which appear or are obscured depending on the excitation conditions. Firstly, the conduction band inter-sublevel s-p transition is excited by the THz pulses. However, for strong terahertz intensities, a loss of photoluminescence is observed, which can lead to total depletion at very high intensities. This is ascribed to the transfer of charge carriers into the wetting layer. Thirdly, for certain near-infrared energies, the opposite behavior is observed, in which the terahertz pulse causes an increase of photoluminescence. The cause of this effect is the release of previously trapped charge carriers, which is also visible in the photoluminescence spectrum. The source of the additional charge carriers is unambiguously identified as the wetting layer. The obtained data is compared to previous studies, and an overview of the relevant theory is presented. In addition, a description of the custom built experimental setup is given.