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Identifier 000423649
Title Study of parabolic quantum well microcavities and time domain terahertz spectroscopy in the bosonic cascade regime
Alternative Title Μελέτη μικροκοιλοτήτων με παραβολικά κβαντικά πηγάδια και terahertz φασματοσκοπία για μποζονικές αλυσιδωτές μεταβάσεις
Author Τζίμης, Αλέξανδρος
Thesis advisor Σαββίδης, Παύλος
Reviewer Κιοσέογλου, Γεώργιος
Δεληγεώργης, Γεώργιος
Πελεκάνος, Νικόλαος
Χατζόπουλος, Ζαχαρίας
Παπάζογλου, Δημήτριος
Αποστολόπουλος, Βασίλειος
Abstract The present dissertation is focused on the study of semiconductor microcavities with embedded quantum wells. The devices are based on the strong coupling between light (photons in a cavity) and matter (excitons in quantum wells), forming new quasiparticles called polaritons. Such structures aim to provide an alternative way of generating THz photons utilizing a bosonic cascade phenomenon. The cascade is based on a series of sequential transitions of bosons from equidistant energy levels and in the process THz photons are emitted. The work presented here is divided into two parts. The first part deals with a study of semiconductor structures based on a single parabolic quantum well. The second part describes the development and evaluation of a THz time domain spectrometer aimed to study bosonic cascade. In the first part we show that the parabolic quantum well exhibits the expected equally spaced excitonic transitions. We observe quantum beating at THz frequencies between the discrete energy levels of quantum well excitons. When a single parabolic quantum well is placed in a microcavity, the full structure shows a clear anticrossing between heavy hole / light hole excitons and the cavity mode, revealing the strong coupling regime. Furthermore, under non-resonant optical excitation, the microcavity exhibits non-linear stimulated emission. In addition, a relaxation dynamics study shows that excitons relax much faster in the parabolic potential compared to a structure with conventional rectangular quantum wells. The theoretical modeling of relaxation dynamics qualitatively agrees with the experimental results and predicts the time evolution of exciton densities at each level of the parabolic quantum well, along with the photoluminescence contribution of each transition. The second part deals with the development and evaluation of a THz time domain spectrometer which allows measurements of THz emission as well as optically induced modulation of THz transmission, gain, and absorption. The setup provides the ability of performing such experiments in cryogenic environment at a temperature range of 14-300 K. Preliminary results on absorption/gain measurements on parabolic quantum well microcavities are also presented.
Language English
Subject Exciton
Light-matter interaction
Terahertz radiation
Ακτινοβολία τεραχέρτζ
Αλληλεπίδραση φωτός-ύλης
Κβαντικό πηγάδι
Issue date 2019-07-26
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Materials Science and Technology--Doctoral theses
  Type of Work--Doctoral theses
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